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JeepLab
04-13-2014, 08:15 PM
Ok, ive just gone thru the ringer with gears. Here’s what Ive learned. Maybe it will save someone else a pile of time and money.
There is a LOT of misinformation on the internet about gears. You really have to ignore it all. People use this chart to understand what gearing is correct, but I disagree with this chart on a few points.

653

Mistake 1. You don’t really know your tire size. I have 37x12.50R17s on Black Betty right? They are not 37 inches tall. I just EXTENSIVELY tested the calibration of my system because I couldn’t figure out why I hated the new gearing so much. Turns out that my truck has to be calibrated as if its tires are 35.5 inches tall. And even there, it was off by about a mile vs. the gps for each 110 miles traveled. You need good distance to really test this, as you are talking about feet difference if your off by an inch. It takes a road trip to make sure its perfect.
You rubicon owners who think you have 32s… you have 31s.

"No ones tires are the total height, everyone knows that, dummy." – Yes I knew it too. But my brain figured that under load, the tire would bulge to the sides and top. So the circumference (length around the outside of a circle) of the tire, should be the same distance per revolution as a 37 inch tire would be. The way I figured it, the tire dosent wrinkle, you have to travel the full distance of the outside revolution and thus, even tho the tire measures 35.40 inches tall, all the bulged sections at the sides and top are still tread that has to pass for a revolution.

Suffices to say. I was wrong. All the extra math I was doing means nothing. BB was only properly calibrated once I dialed her in with her tire size as the standard height. Straight from bottom to top. Totally over thought it.


Mistake 1 – selected gears based on my “imagined” tire size. LOL. When using that chart realize that your tire size is not the size you bought.

Mistake 2 – Chasing the crusing gear. With 4.10s, BB would cruise at 80 mph at 2500 rpm. Great right? I couldn’t figure out why I was losing soooo much speed with the new gears. I was expecting the difference to be few hundred rpm. Well Im here to tell you, 400 RPM is a lot. But the bigger problem was that I was calibrated correctly after the gear change, and I WASN’T before. So Im driving around thinking I have 37s on, calibrated for 37s, speedo responding like I had 37s….with 35.5s on.

Point is, I wasn’t doing 80 at 2500 rpm. So the draw back I experienced was compounded with the realization that the speedo has been lying to me for 6 months. Not by a lot, but enough to shock me when the 4.88s went in.

Keep in mind, Tires wear, and everyone runs at different PSI, My KM2s have about 4k miles on them, and im not sure how much I could have lost, but realize that we are talking about calibration, that relys on a rubber component that wears as you drive. So your gearing and speedo calibration is going to increase as the tires get smaller. You have to study your own truck to know where to start in order to use the charts correctly.

Let me know if im overthinking again.

Mistake 3 – being afraid of the yellow section of the chart. – Everything they say about the yellow section is negative. Minimum acceptable for daily driving. Maybe that’s true without the supercharger. (just realized that’s the xfactor here) but outside of that, the yellow section allows you to cruise at high speed on the highway.

If you don’t drive on the highway, fine. I don’t do it a lot, but when I do, Its long distance. And having to hold the gas pedal down further to maintain 2500 rpm to do 70 mph is taxing. For rubicon owners, especially in the north east where highways move at 80mph, You have a 4 to 1 transfer case, so when you go into 4 low off road, your truck makes up for this Yellow level of gearing, So you have the option to have a higher cruise speed on the road, without really giving up anything off road.

Ross from Ripp supercharger once warned me not to regear for this exact reason. I didn’t listen to him and he was right.

Mistake 4 – reading forums. – Yes, ill admit it. I was influenced by forums stating that 37s require 4.88s. I’ve realized that any idiot can open a forum account and blab about whatever they want. Valuable lesson, as a lot of my jeep knowledge comes from others and tons of research. When it comes to gears, ignore the forums. You have to buy them, and spend to install them before you ever find out if you’ll like them. Its invasive and risky. A lot can go wrong. So before you take out 4.10s think long and hard about it.

IF you have 3.21s and want to go to larger tires… Consider 4.10s or Yukon makes them as 4.11s They are the most expensive gear, but don’t let that scare you. Doing this twice is far more expensive.

Keep in mind, lots of people just repeat the garbage that others said without actually having that gear installed and lived with it. There is accurate information on the internet also, but for everything I read that gave the correct information I found 20 other posts that disagreed and gave bad information. Not everyone who talks like an authority is an authority. You need to check post count, and refrences.

Mistake 5 – Not realizing that manual trans is far different from auto for gearing requirements.

Many of the people yapping online have autos. This makes a huge difference. Autos need new gear more than manuals. Because your pretty much on autopilot and at its mercy to select which gear to drive in. Your also confusing it with larger tires. People regear autos and it makes a big difference because the get better acceleration because they may be stuck in a higher gear as the cpu is deciding which gear is right.

In a Manual trans, if 6th gear is your crusing gear, ignore it until you need it. If you need more torque, downshift. This higher level of control means that you can compensate for taller gears with your own brain, rather than change the gears.

Overall information.

- 10% of the people who talk in forums are the ones giving out the info, the other 90% are the ones reading and commenting, but not being authorities. The way you become an authority is with experience. Normally these people will have large tires, and new gears, and metal flares, their rigs are crazy. They rock crawl moab, and rubicon trail etc. You know what is better for rock crawling? An automatic transmission. We were on the trail with RK and RIPP and about 50 rigs. There was one manual transmission there. Black Betty.

- Taller gears- people think taller gears have higher numbers, the high numbers are smaller gears. 3.21 is "taller" than 4.10

JeepLab
04-13-2014, 08:17 PM
Here is a bigger chart

654

JeepLab
04-13-2014, 08:18 PM
Notes on the situation,

Went from 4.10s to 4.88s with manual Trans and 37s. Was over geard and dialed it back with 4.56s

UselessPickles
04-13-2014, 08:43 PM
Here's the chart for the 3.6 engine:

http://farm8.staticflickr.com/7159/6395189429_b39b861446_z.jpg

I'm dreading making the gearing decision. I have the 3.6 engine, manual transmission, 3.21 gears and the smallest stock tires (29"?). I eventually plan to go up to 33x12.5x15 Duratracs. I'm happy with the way it drives stock, and 3.73s would get me slightly shorter overall gearing with the 33's (which are actually more like 32" or 32.5") than I have right now. I think I'm going to have to ignore all the typical forum comments about "if you're going to re-gear from 3.21, then at least go to 4.10, or else you'll regret it and re-gear again."

I'm really just going to have to wait and see how the 33s do with 3.21 gears. I plan to have some sort of forced induction, and I have a light-weight 2-door with no plans for heavy bumpers, etc. It might be just fine with 3.21s

JeepLab
04-13-2014, 09:26 PM
Here's the chart for the 3.6 engine:

http://farm8.staticflickr.com/7159/6395189429_b39b861446_z.jpg

I'm dreading making the gearing decision. I have the 3.6 engine, manual transmission, 3.21 gears and the smallest stock tires (29"?). I eventually plan to go up to 33x12.5x15 Duratracs. I'm happy with the way it drives stock, and 3.73s would get me slightly shorter overall gearing with the 33's (which are actually more like 32" or 32.5") than I have right now. I think I'm going to have to ignore all the typical forum comments about "if you're going to re-gear from 3.21, then at least go to 4.10, or else you'll regret it and re-gear again."

I'm really just going to have to wait and see how the 33s do with 3.21 gears. I plan to have some sort of forced induction, and I have a light-weight 2-door with no plans for heavy bumpers, etc. It might be just fine with 3.21s

We need snarf to weigh in, He just geared to 4.88 with 37s and no forced induction.

GizmoGoat
04-13-2014, 09:38 PM
Both my wife and I have 2014 JK unlimited rubis. Both equiped with autos trans. I have 4.10 she has 3.73 and honestly say I do not know which I prefer. We do quit of bit of highway driving on a daily basis 60-85 mph range. Thinking about it as i type I think I enjoy the 3.73 for highway driving and 4.10 for city driving. I too am considering a gear change for my rubi as I'm going with 3.5 inch lift and 34.5ish tires, and will also be adding forced induction to my build as well. I'm going with the wait and see method- do my mods drive around for a while and see if have to go down to 4.56.

JeepLab
04-13-2014, 09:44 PM
Both my wife and I have 2014 JK unlimited rubis. Both equiped with autos trans. I have 4.10 she has 3.73 and honestly say I do not know which I prefer. We do quit of bit of highway driving on a daily basis 60-85 mph range. Thinking about it as i type I think I enjoy the 3.73 for highway driving and 4.10 for city driving. I too am considering a gear change for my rubi as I'm going with 3.5 inch lift and 34.5ish tires, and will also be adding forced induction to my build as well. I'm going with the wait and see method- do my mods drive around for a while and see if have to go down to 4.56.

Do the gears last. The forced induction may change your opinion of what gears will be best. If you are staying under 35 inches for tires, I think you'd be nuts to alter them.

GizmoGoat
04-14-2014, 12:12 AM
Notes on the situation,

Went from 4.10s to 4.88s with manual Trans and 37s. Was over geard and dialed it back with 4.56s

Very interested on how the 4.56 work out for you. Post your finding for evaluation.

ljvsnyder
04-14-2014, 09:52 AM
Well, mine is an uneducated opinion, but seat of the pants feel and may not be all that useful. I recently changed my tires from 225/75-16's to 285/75-16's both running on the stock steel wheels and 3.73 gears. Can I tell there was a change, absolutely, plus the tires with 35 psi measure 31.75", I recalibrated with a procal and got the speedo within .6 mph. I have lost about 1.2 mpg, based upon the last 5 hour road trip that included a lot of slow hill driving on tight forest roads. The JK did great both on highway and offroad. Would 4.10's give me better acceleration, yes. Do I want to waste money on regearing for these tires no, especially since I plan in the long run to change out axle housings and gears in the future and putting on larger tires. But for now this is a DD and it isn't necessary to change them at this time. If I had 3.21 with 33" tires and wanted to change I would look for a set of 3.73's from someone who needed 4.10 or something smaller.

Must say Jeep Lab great write up. I like the other forums, but have been finding myself coming here for a lot of information lately.

Snarf77
04-14-2014, 05:24 PM
Let's not discount the categorical colors in the chart. First, I'm speaking as a person with a naturally aspirated 3.6 Rubicon 6MT 2door. I recently added my lift and 37' KM2s and geared to 4.88. I also did a ton of research and chose 4.88s specifically for the improved gear ratio for crawling off road, even with my Rubicon T-case. The color charts above, even with at 36" actual tire size, put me at a low/middle mark in the "blue" or performance category. This is great to me and she drives better than stock around town when accelerating at in-town speeds, up to 60mph or there abouts. Point is, though I have the 4.88s, my vehicle's use is different from Ross' (e.g. 80mph highway) and I made the decision to gear at 4.88. Seems great for now, and I'm very happy. The most highway driving I'll do in Jesse's Girl will be about 2 hours to the off road park. I have a second 40mpg vehicle for the highway.

The REAL test will be when I move to forced induction adding more power and torque. I see Ross' point being entirely probable in the prediction that when I have more power, the same 4.88 gears that made my jeep drive well with 37s, could actually serve to hold my jeep hostage to the new found power.

If that is the case, then so be it and I'll have to make the change. Either way, I'll let everyone in Jeeplab know my opinion as objectively as possible!

JeepLab
04-14-2014, 08:45 PM
Well, mine is an uneducated opinion, but seat of the pants feel and may not be all that useful. I recently changed my tires from 225/75-16's to 285/75-16's both running on the stock steel wheels and 3.73 gears. Can I tell there was a change, absolutely, plus the tires with 35 psi measure 31.75", I recalibrated with a procal and got the speedo within .6 mph. I have lost about 1.2 mpg, based upon the last 5 hour road trip that included a lot of slow hill driving on tight forest roads. The JK did great both on highway and offroad. Would 4.10's give me better acceleration, yes. Do I want to waste money on regearing for these tires no, especially since I plan in the long run to change out axle housings and gears in the future and putting on larger tires. But for now this is a DD and it isn't necessary to change them at this time. If I had 3.21 with 33" tires and wanted to change I would look for a set of 3.73's from someone who needed 4.10 or something smaller.

Must say Jeep Lab great write up. I like the other forums, but have been finding myself coming here for a lot of information lately.

1. why change housings? Run that D30 till you break it. If you want to toughen it up, do an artec armor kit. Especially if you dont think your going to make it to 35s.

2. definatly look for gear take offs, if your not looking to go past 4.10.

3. I would help others do gears and learn to do it yourself. That will really cut the expense. Ive watched once and i think i have a grip on how to do it now.

4. ROCK LOBSTA!!! - I saw a winterchill jk a few weeks ago. It was the only time i envied another guys color. My black xpel wrapped paint is timelessly beautiful, but there are 300 winterchill rubicons on earth. How may rock lobsters are there? Not many. Great color choice. BOLD!

JeepLab
04-14-2014, 08:48 PM
Let's not discount the categorical colors in the chart. First, I'm speaking as a person with a naturally aspirated 3.6 Rubicon 6MT 2door. I recently added my lift and 37' KM2s and geared to 4.88. I also did a ton of research and chose 4.88s specifically for the improved gear ratio for crawling off road, even with my Rubicon T-case. The color charts above, even with at 36" actual tire size, put me at a low/middle mark in the "blue" or performance category. This is great to me and she drives better than stock around town when accelerating at in-town speeds, up to 60mph or there abouts. Point is, though I have the 4.88s, my vehicle's use is different from Ross' (e.g. 80mph highway) and I made the decision to gear at 4.88. Seems great for now, and I'm very happy. The most highway driving I'll do in Jesse's Girl will be about 2 hours to the off road park. I have a second 40mpg vehicle for the highway.

The REAL test will be when I move to forced induction adding more power and torque. I see Ross' point being entirely probable in the prediction that when I have more power, the same 4.88 gears that made my jeep drive well with 37s, could actually serve to hold my jeep hostage to the new found power.

If that is the case, then so be it and I'll have to make the change. Either way, I'll let everyone in Jeeplab know my opinion as objectively as possible!


Hang on to those 4.10s. You may be going back....

Rexx19
04-14-2014, 11:21 PM
soooo the sc works kinda like gears itself?

ljvsnyder
04-15-2014, 10:14 AM
One day this will be a dedicated offroad vehicle and I am sure the D30 will be broke before it is changed out. I wasn't sold on the Lobster at first, but man I have grown to love it. There aren't many around, and they were discounting the price to get rid of this one instead of ordering a 2014.

Timmy
04-15-2014, 04:44 PM
First time posting! Just picked up a 2014 JKU lifted with 35" tires.

Thanks JeepLab for all your article, posts and write-ups. I have been following the supercharger article for about 2 weeks now and I'm excited to pick up a Magnuson SC in the next few months. I found your post here very timely as I've been driving around in my new JKU and considering gearing. I have a 4" lift, 35" tires (and as you said, they actually _measure_ 34") and 3.73 gears. As I've driven down the highway at 70 to 75 mph, I have certainly seen that the Jeeps don't handle 6th gear very well there, in fact you are rarely in 6th gear. I can appreciate everyone wanting to re-gear, but as I've read, I had already been coming to the same conclusion as you, people are really messed up about gearing.

For me... I just came from a 2009 Audi A4 with the 2.0T engine (chipped.) That thing was a little rocket at any speed. Here's the thing I find interesting and what I took away from driving that vs. my JKU. Everyone seems to think they are suppose to be able to cruise in 6th gear at highway speeds all the time, and maybe even overtake/pass in that gear. Well, my little rocket of an Audi would cruise in 6th at highway speeds, but when I went to overtake, it dropped down pretty quick to a lower gear (sometimes all the way to 3rd.) 6th gear simply didn't have overtaking power (within reason, it did at 100mph) and that's why the car had 6 gears. That last gear was for economy, and it would drop to 5th in a second to go up a hill. Shoot, now they have 8 gears. Can you imagine an 8 speed JKU and everyone trying to gear for the 8th gear to be able to overtake at highways speeds. Ugh...

I keep reading about people re-gearing a Jeep to try to get 6th gear cruising above 2000 RPM at 70 mph, and I'm thinking, ARE YOU CRAZY!!! Once you gear that high, your screwed, you can't magically drop the RPM's back down to get good gas mileage. However, if you are geared so 6th gear has lower RPMs at highway speed, you can ALWAYS drop down to 5th gear to get the RPM's up. Long story short, I came to the same conclusion you did, be slower to re-gear a Jeep vs. what everyone else is saying. Seems like the majority of the issues with lower RPM's and highway speeds would be resolved with more power (like a supercharger.) At this point, I'm convinced if I do re-gear after getting an SC, I'm not going above 4.11 gearing.

Another case in point... My wife drives a 2013 Ford F350. That has a monster turbo on it that can pump in 40 psi to the engine The other day I was driving at highway speeds and the truck was in sixth gear, and the turbo was registering a constant 4 to 5 psi of boost the entire time on a level highway while the RPM's were down at around 1700 or 1800. Tap the gas slightly and the boost kicked in quick so that it didn't have to drop to 5th gear as quickly, but it still would if you pressed more. My experience with all of my different vehicles over the years has me feeling like I'd rather spend the money on a supercharger and see how 3.73 gears perform with an added extra 100+ hp. I have to assume that the extra 100hp at highway speed with a touch of constant boost like my Ford does will do plenty to help compensate for an RPM range designed for better gas mileage.

Anyway, just my two cents. I'm sure I'll get plenty of comments like "newbie that hasn't driven in the mountains" (I'm from Colorado, BTW, plenty of mountain driving) to "wait until you have the vehicle for more than a week."

Thanks again JeepLab.

JeepLab
04-15-2014, 08:16 PM
Anyway, just my two cents. I'm sure I'll get plenty of comments like "newbie that hasn't driven in the mountains" (I'm from Colorado, BTW, plenty of mountain driving) to "wait until you have the vehicle for more than a week."

Thanks again JeepLab.

WELCCOME!

I doubt you'll get those responses here.

Gotta look at the pentastar with fresh eyes. People who are hard core about gearing are usually people coming from JKs and older jeeps with the 3.8 liter engine or earlier. Those truck needed gears.

Maybe those guys have bought 12s and up, but their brains are trapped in 3.8 thinking.

Regearing is good. but you just have to be smart about it. And see it for what it is. Its the WORST thing to have to do twice.

Pznivy
04-17-2014, 02:11 PM
The ideas in this thread are definitely not going along with mainstream opinion. I like that you are not afraid to disagree with the public at large.

objectivity.

Now. that being said. I am about to regear. Do you guys have a brand you like? I see you used all yukon stuff. They are a little more expensive, what made you go with them?

Rexx19
04-19-2014, 09:43 PM
The ideas in this thread are definitely not going along with mainstream opinion. I like that you are not afraid to disagree with the public at large.

objectivity.

Now. that being said. I am about to regear. Do you guys have a brand you like? I see you used all yukon stuff. They are a little more expensive, what made you go with them?

I think all gears come from some korean factory... but yukon is the way to go for service. The guys there, will not allow a problem. Somethings wrong? They will get to the bottom of it....And not just try to sell you more stuff to try again.

JeepLab
04-21-2014, 07:07 PM
Rexx got it right.

Yukon is going to be in my estimation the closest thing to mopar gears. A hint of a problem, and the Yukon guys go into disection mode. They get to the bottom of a buzzz, a wrrrrrrrr, anything you can describe, they will spring to correct.

It also helps that yukons very rarely need correction.

You really need to pick a good shop that is close to your house. once the new stuff goes in, you dont want to drive far.

Deola
04-23-2014, 11:42 AM
I'm Baaacccckkkk. This is a great write up! Several excellent points made, after my install I will have some more to add.

JeepLab
05-12-2014, 09:10 PM
The 4.56 gearing is growing on me. The SC has some extra zing around town. and still cruises fast on the highway.

WhiteRavenRR
05-13-2014, 06:51 AM
This is a great thread. I'm stuck in 3.8l thinking because I have a 3.8l. :( I will be looking at gears sometime in the future. I don't ever see myself going bigger than 35's so I'm thinking along the lines of 4.88. I'm running factory 4.10s in an automatic with a Dana 30. The supercharger would be an interesting addition to the fold. I would like to see some real world numbers for the 3.8l regarding gears with and without a supercharger.

JeepLab
05-14-2014, 08:48 PM
This is a great thread. I'm stuck in 3.8l thinking because I have a 3.8l. :( I will be looking at gears sometime in the future. I don't ever see myself going bigger than 35's so I'm thinking along the lines of 4.88. I'm running factory 4.10s in an automatic with a Dana 30. The supercharger would be an interesting addition to the fold. I would like to see some real world numbers for the 3.8l regarding gears with and without a supercharger.

Figure out if you are going to supercharge or turbo you truck. That will alter how you feel about gears.

Blower first.

Timmy
03-23-2015, 12:00 PM
Reviving this old thread. Just about to order my 4.56 gears. Just to be sure, I did some more research to make sure I didn't want to go to 4.88's. I really don't do much highway driving above 70 Mph, so it almost made sense, but in the end I decided to just stick with 4.56.

I found the following web site incredibly helpful to making the decision: http://www.4ws.com/gear-ratio-rpm-calculator

It allowed me to drop in the most accurate gear ratios I could find for first-thru-sixth gear. I put in my measured tire dimension of my new 37" tires, and then compared that to my old 35" tires in terms of what I was feeling, and then just kept bopping between different gears to see where things landed. With my old 35" tires, I was moderately happy with my 3.73 gear ratio. I kept feeling that it could use a bump to 4.10, but overall I could handle 3.73. I see that with my 37" tires, at 4.56 gearing, I would be slightly higher in gearing than my 35" tires at 4.10 gearing, so that ended up being the deciding factor for me. I think that 4.88 would have just been too tall. I have found out that Chrysler seems to have changed sixth gear from the 0.83 gearing that is often quoted to 0.797, so if you use the link provided above, make sure you double check the numbers from the built-in "Pre-Filled" drop down list, as those numbers do not appear to be 100% accurate.

Here is what the tool was showing for me between the 4.56 and the 4.88 gearing.
4.56
1561

4.88
1560

JeepLab
03-23-2015, 07:53 PM
Reviving this old thread. Just about to order my 4.56 gears. Just to be sure, I did some more research to make sure I didn't want to go to 4.88's. I really don't do much highway driving above 70 Mph, so it almost made sense, but in the end I decided to just stick with 4.56.

I found the following web site incredibly helpful to making the decision: http://www.4ws.com/gear-ratio-rpm-calculator

It allowed me to drop in the most accurate gear ratios I could find for first-thru-sixth gear. I put in my measured tire dimension of my new 37" tires, and then compared that to my old 35" tires in terms of what I was feeling, and then just kept bopping between different gears to see where things landed. With my old 35" tires, I was moderately happy with my 3.73 gear ratio. I kept feeling that it could use a bump to 4.10, but overall I could handle 3.73. I see that with my 37" tires, at 4.56 gearing, I would be slightly higher in gearing than my 35" tires at 4.10 gearing, so that ended up being the deciding factor for me. I think that 4.88 would have just been too tall. I have found out that Chrysler seems to have changed sixth gear from the 0.83 gearing that is often quoted to 0.797, so if you use the link provided above, make sure you double check the numbers from the built-in "Pre-Filled" drop down list, as those numbers do not appear to be 100% accurate.

Here is what the tool was showing for me between the 4.56 and the 4.88 gearing.
4.56
1556

4.88
1557

what is going on with these attachments? and im sure you will be happy with 4.56.

Timmy
03-23-2015, 09:57 PM
what is going on with these attachments? and im sure you will be happy with 4.56.

That's weird, I'm not sure what happened to attachments. I just re-uploaded them and they came in this time. Go figure...

I will say, I'm still slightly on the fence about the 4.88's. I rarely drive about 65 Mph, as there is just not that much around me where the speed limits are 70Mph+. Also, there is a chance I may tow some things. I think the *safe* answer is the 4.56, as I trust JL on his experience here, but I am itching for the 4.88's if it will help my low range since I don't have the Rubicon transfer case ;-(

dalearyous
03-23-2015, 10:53 PM
I wanted to chime in here. I have 2013 JKUR with 35s (nitto trail grapplers that measure very close to 35s) and 6 speed. I recently re geared from stock 4.10s to 5.13s. I was extremely anxious and nervous about going with such an aggressive gear. But 37s are in my future so I wanted to be ready. I agree with initial post that there is a lot of garbage on the Internet about gears and the chart is over analyzed.

I wanted to say (from my experience only, have not driven 4.88 auto) that I am extremely happy with 5.13s. 1st gear is still useful and I start from it. Sure I have to shift a bit more but the 6 speed obviously lets me choose when. The highway is now enjoyable. I can stay and cruise in 6th gear and accelerate uphill at 70+ miles and all under 3k RPMs. If I couldn't see the needle I would think I was cruising at stock RPMs.

My two ignorant cents. I love my Yukon 5.13s. I don't have SC or TC.

JeepLab
03-24-2015, 08:23 AM
I wanted to chime in here. I have 2013 JKUR with 35s (nitto trail grapplers that measure very close to 35s) and 6 speed. I recently re geared from stock 4.10s to 5.13s. I was extremely anxious and nervous about going with such an aggressive gear. But 37s are in my future so I wanted to be ready. I agree with initial post that there is a lot of garbage on the Internet about gears and the chart is over analyzed.

I wanted to say (from my experience only, have not driven 4.88 auto) that I am extremely happy with 5.13s. 1st gear is still useful and I start from it. Sure I have to shift a bit more but the 6 speed obviously lets me choose when. The highway is now enjoyable. I can stay and cruise in 6th gear and accelerate uphill at 70+ miles and all under 3k RPMs. If I couldn't see the needle I would think I was cruising at stock RPMs.

My two ignorant cents. I love my Yukon 5.13s. I don't have SC or TC.

not ignorant, but id ask, what is the RPM you run at when driving 70mph?

is your tach and speedo corrected for the gears?

dalearyous
03-24-2015, 08:52 AM
i guess i should have said inexperienced instead of ignorant. i only know what i have and i have not driven anything else other than stock rubicons and stock sports.

i have the superchips flashpaq 3872 and have tried to dial in the tach and speedometer as close as possible. i have done the unscientific verification with my wife following me as well as tried to measure distance. basically, at 70 mph im running rite around 2700 rpms. obviously resistance will change that a bit. wind against me its a little higher, wind behind me its a little less. 75mph runs around 2800 ish. 80mph is like right at the 3000 rpm mark. i know the RPMs seem high but the jeep seems to be perfectly fine at those RPMs. like i said, i don't feel like i am taxing it more than lets say 2700 RPMs. i think with 37s it will be perfect which is what i was going for. i am in virginia where the highways are 70 mph speed limit so i go 75 and happy to cruise there.

now if i had your supercharger i would probably be singing a different tune. but most people don't have a super charger so they post about what they have, HOPEFULLY. but yes to your original post, i would completely throw away someone's post about gears when their signature states they are stock or running stock gears on lift and bigger tires. you just don't know until you do it and i think that is the fear and why there are so many threads about it.

btw, snarf and i have had a LOT of conversations on the wrangler forum. seems like a solid guy.

Timmy
03-24-2015, 10:05 AM
i have the superchips flashpaq 3872 and have tried to dial in the tach and speedometer as close as possible

i have done the unscientific verification with my wife following me as well as tried to measure distance. basically, at 70 mph im running rite around 2700 rpms. obviously resistance will change that a bit. wind against me its a little higher, wind behind me its a little less

Durp? You just be-futtled my brain... I'm hoping I'm just reading this wrong, but I wouldn't think you would be able to "dial in the tach," and I can't imagine your RPM's would change based on resistance?

Very curious... Why not just set your cruise control at 70Mph and then use the GPS on your phone to tell you how fast you are going and then use Superchips to adjust your speedo as needed until it is dead-on accurate? This is what I did with my AEV Procal. I programmed for what was suppose to be the correct tire size, went out on the road and verified and then adjusted as needed. Right now I'm running exactly 1 Mph slower than what my speedo says. I could correct that so it is dead accurate but I'm leaving it that way in case anyone else drives my Jeep so they have just a slight buffer should they ever get pulled over.

dalearyous
03-24-2015, 10:42 AM
should have clarified: ok yeah obviously you can't adjust the tach, i meant the ratio of RPMs to speed. anyway, to clarify the resistance: i was referring to the amount of RPMs need to sustain a speed with the cruise on. your vehicle is obviously going to work harder if you are driving straight into a strong wind and so you get that slight fluctuation (in speed and RPMs). all i was referring to.

i don't like trusting a GPS for my speed. my OBCD dongle has an app that allowed me to basically drive one mile at a constant speed (again as best i could) with a timer and then i did the math. i always found GPS to be 1-2 MPH slower than actual speed.

Timmy
03-24-2015, 12:00 PM
should have clarified: ok yeah obviously you can't adjust the tach, i meant the ratio of RPMs to speed. anyway, to clarify the resistance: i was referring to the amount of RPMs need to sustain a speed with the cruise on. your vehicle is obviously going to work harder if you are driving straight into a strong wind and so you get that slight fluctuation (in speed and RPMs). all i was referring to.

i don't like trusting a GPS for my speed. my OBCD dongle has an app that allowed me to basically drive one mile at a constant speed (again as best i could) with a timer and then i did the math. i always found GPS to be 1-2 MPH slower than actual speed.

Ahh, got it.

I agree with you, some GPS can be a little off. Of course, if the GPS is consistent, that's what matters most as that is something you can work with (either consistently above or below.) I have found when I calibrate to GPS and then I cruise past one of those stationary pole mounted radar guns that displays your MPH, that my MPH displayed in the dash matches pretty close to what the radar gun shows on the pole, so I think the GPS is close enough. Also, it's usually good to be a little high on the speedo as it helps save you a ticket. That's why most German cars have a built in 3% margin to the high side ;-)

KaiserBill
03-24-2015, 04:28 PM
should have clarified: ok yeah obviously you can't adjust the tach, i meant the ratio of RPMs to speed. anyway, to clarify the resistance: i was referring to the amount of RPMs need to sustain a speed with the cruise on. your vehicle is obviously going to work harder if you are driving straight into a strong wind and so you get that slight fluctuation (in speed and RPMs). all i was referring to.

i don't like trusting a GPS for my speed. my OBCD dongle has an app that allowed me to basically drive one mile at a constant speed (again as best i could) with a timer and then i did the math. i always found GPS to be 1-2 MPH slower than actual speed.


GPS systems have a percentage of error like anything else.

JeepLab
03-24-2015, 07:29 PM
i guess i should have said inexperienced instead of ignorant. i only know what i have and i have not driven anything else other than stock rubicons and stock sports.

i have the superchips flashpaq 3872 and have tried to dial in the tach and speedometer as close as possible. i have done the unscientific verification with my wife following me as well as tried to measure distance. basically, at 70 mph im running rite around 2700 rpms. obviously resistance will change that a bit. wind against me its a little higher, wind behind me its a little less. 75mph runs around 2800 ish. 80mph is like right at the 3000 rpm mark. i know the RPMs seem high but the jeep seems to be perfectly fine at those RPMs. like i said, i don't feel like i am taxing it more than lets say 2700 RPMs. i think with 37s it will be perfect which is what i was going for. i am in virginia where the highways are 70 mph speed limit so i go 75 and happy to cruise there.

now if i had your supercharger i would probably be singing a different tune. but most people don't have a super charger so they post about what they have, HOPEFULLY. but yes to your original post, i would completely throw away someone's post about gears when their signature states they are stock or running stock gears on lift and bigger tires. you just don't know until you do it and i think that is the fear and why there are so many threads about it.

btw, snarf and i have had a LOT of conversations on the wrangler forum. seems like a solid guy.

Snarf is more technical than I am. where Im inches, he is millimeters. However, My brain cannot comprehend you having 5.13, AND 35s (which are really less) and still having a comfortable highway cruise. Something is off somewhere. With 4.88s and 37s, I struggled to maintain 75mph.

Thats why I asked if your tach and odometer were calibrated correctly.

I drove for a loooong time with them out of wack and never knew it. Till i tested with a 2 hour drive.

dalearyous
03-24-2015, 07:52 PM
snarf helped me with my metalcloak bumpers and suspension when i was making my decision.

i can take a video if you would like. i was thinking about doing one anyway because of all the questions i have gotten with 5.13s.

"comfortable highway cruise" - whats not comfortable to you? we could have a very different frame of reference, what are you comparing it to?

oh also how does it compare to snarf's experience? he went with 4.88s

*edit*

With 4.88s and 37s, I struggled to maintain 75mph.

the way my local shop explained it to me is that they told me to ignore the garbage on the internet and just go with what it feels like (these guys have been 4x4 racing for 15 years). they said 4.88s with 37s (what i will have eventually) is going to feel like stock rubicon with 4.10s and 31s or whatever is on them. if you want to get back to stock feel with 37s, you go 4.88s. if you want something that feels better, go with 5.13s and 37s. this was tough for me, but he laughed and said let your engineer/comp science brain go for a minute and just trust me. if you want it to feel better than stock on 37s, go 5.13s. so i did on 35s for now.

again, more horsepower changes a lot so i have no idea what a turbo or super charger changes but going with "the feel" feels good right now. i would probably never go 5.13s if i had an LS for example.

Timmy
03-24-2015, 11:22 PM
With 4.88s and 37s, I struggled to maintain 75mph.

Hey Ross, you've mentioned this a few times now and I was curious... Why do you feel it struggled to maintain 75mph with 4.88's? I'm guessing at 75mph you were around 2900 RPM in sixth gear? (based on that tool I published and punching in your measured tire size.) I'm very surprised that at 2900 RPM it was struggling at 75 Mph? I actually would have thought the exact opposite would happen with the 4.56 gears? 4.56 Gears appears to be hitting 75 Mph at 2700 RPM so I would have thought it would be more of a struggle say if you hit an uphill section? I mean, technically, isn't this like saying you couldn't hit 75Mph by downshifting to 5th because the RPM's went to 3200?

Not doubting your personal experience as I fully trust you when you say 4.88's were not as good as 4.56's on the highway, but I'm wondering if you could elaborate more on why you feel the 4.88's struggled so much?

Snarf77
03-25-2015, 09:25 AM
My 2 Door with boost will maintain 90 with no problems...not that its a good idea. 70 was a non issue with 37 KM2s and 4.88s. Like Dalearyous said, its probably good advice to go with what feels right. Maybe drive someone else's vehicle with the gearing desired to see if it has the right feel? Might take some time but still, you could potentially avoid a mistake.

JeepLab
03-26-2015, 07:29 AM
My 2 Door with boost will maintain 90 with no problems...not that its a good idea. 70 was a non issue with 37 KM2s and 4.88s. Like Dalearyous said, its probably good advice to go with what feels right. Maybe drive someone else's vehicle with the gearing desired to see if it has the right feel? Might take some time but still, you could potentially avoid a mistake.

maintain 90 at what RPM? 3500?

JeepLab
03-26-2015, 07:38 AM
Hey Ross, you've mentioned this a few times now and I was curious... Why do you feel it struggled to maintain 75mph with 4.88's? I'm guessing at 75mph you were around 2900 RPM in sixth gear? (based on that tool I published and punching in your measured tire size.) I'm very surprised that at 2900 RPM it was struggling at 75 Mph? I actually would have thought the exact opposite would happen with the 4.56 gears? 4.56 Gears appears to be hitting 75 Mph at 2700 RPM so I would have thought it would be more of a struggle say if you hit an uphill section? I mean, technically, isn't this like saying you couldn't hit 75Mph by downshifting to 5th because the RPM's went to 3200?

Not doubting your personal experience as I fully trust you when you say 4.88's were not as good as 4.56's on the highway, but I'm wondering if you could elaborate more on why you feel the 4.88's struggled so much?

When i say "struggled" thats probably not the best word. The Jeep was fine getting to those speeds, but the pressure i had to hold on the pedal to get there was uncomfortable, keeping the truck at 2600 rpm is not her sweet spot for cruising. So if i wanted to do 75 for a long distance with 4.88s, I had to really hold the pedal down farther than normal. She didnt comfortably cruise at 75. Or 70 for that matter.

2900 rpm to do 75mph is a LOT of rpm to me. I dont think the truck wants to spin at that level for an extended trip either. Or maybe i dont like to hear the engine working harder than it should in a cruising situation.

With 4.10, I would cruise at 75 at about 2k rpm. She was a road trip killer. Now she isnt quite the same cruiser she was, but the overall acceleration is better.

Now I cruise at 70 at around 2200 rpm. Or somewhere around there. I thought 4.88 was unlivable. Could i get to high speed? yes. Did I have to flog BB to get there? also yes. In NJ people do 80 mph on every highway. If your not up there, you are a slug.

dalearyous
03-26-2015, 09:54 AM
but the pressure i had to hold on the pedal to get there was uncomfortable, keeping the truck at 2600 rpm is not her sweet spot for cruising. So if i wanted to do 75 for a long distance with 4.88s, I had to really hold the pedal down farther than normal. She didnt comfortably cruise at 75. Or 70 for that matter.

2900 rpm to do 75mph is a LOT of rpm to me. I dont think the truck wants to spin at that level for an extended trip either. Or maybe i dont like to hear the engine working harder than it should in a cruising situation.

With 4.10, I would cruise at 75 at about 2k rpm. She was a road trip killer. Now she isnt quite the same cruiser she was, but the overall acceleration is better.

also yes. In NJ people do 80 mph on every highway. If your not up there, you are a slug.

couple things here. holding the pedal down would imply you require more throttle and maybe the jeep wasn't in its optimal power band (HP)? glancing at the pentastar chart this would appear to be true and you were asking a lot from it at that RPM. i dunno, spit balling here.

not wanting to hear the engine working harder than it should? isn't that what a supercharger basically does? i also don't see how you could cruise at 75 mph at 2k rpms. my jeep stock had trouble maintaining 75 because in 6th gear because the RPMs were so low.

now yes, in NJ, you better be driving fast to survive on the highways and i bet it sucks.

anyway a lot of this is circumstantial and i have to agree with snarf, drive what feels best. clearly with your setup 4.56 drives best. it would be very hard to duplicate that as i don't know anyone in person that has a turbo or super charger. and maybe you can get away with 4.56 on 37s BECAUSE of the super charger ... or if you have a free RIPP supercharger i would be happy to be a guinea pig ;)

Timmy
03-26-2015, 12:00 PM
When i say "struggled" thats probably not the best word. The Jeep was fine getting to those speeds, but the pressure i had to hold on the pedal to get there was uncomfortable

That makes more sense, thanks for elaborating on that. And I do totally understand what you are talking about. I was driving down the road this morning at 40mph, with my 3.73 gears, and I had shifted into 5th gear and I was at 1400rpm just to save some gas. The 3.6L has enough power that it could not only maintain 40mph, but I could actually accelerate slightly if I wanted to (and I do mean slightly.) If I needed a hair more power, I downshifted to 4th which brought me to 1600-1700rpm and I could accelerate without much issue. Maybe that's why I'm getting 16.5mpg in my city driving on my 37" tires (and yes, my speedo is calibrated) versus a lot of other guys only getting 13mpg.

As I was driving, I was thinking about our gearing conversations and how if I was at 75mph on the highway in 6th gear, I would be pissed off that I was at 2700 RPM when clearly the 3.6L can cruise at a much lower RPM. I remember when I had my 35" tires on and I would drop into 6th gear all the time on flat surfaces and cruise at 1700-1800 RPM (55mph-60mph) very happily. 6th gear is suppose to be an "overdrive" gear, not a passing gear, right? I think that's why I see so much conflicting information on the web and when I talk with people. It's like people want 6th gear to be able to accelerate up a descent hill on the highway. Maybe in a little 4 door sedan that has a low drag coefficient you could do that, but in a mobile brick with 37" tires that just doesn't seem a good use of the power band.

I've gone back and forth on the 4.56 and 4.88 decision. One day I think I want to try the 4.88's, then, like today, I'm thinking I'd be dumb to do that when like you and I want to see my RPM's spinning lower as it is quieter, smoother and more gas friendly. The reality is, on 35" tires, my 3.73 gears were *almost* fine for me. I was mostly happy, wishing I had just a hair more low-end. I probably would have been happiest at 4.10 gearing with those tires. When I calculate out what 4.56 gearing looks like with my 37" tires, it is actually just a hair more aggressive than what 4.10 gearing would have been with my 35" tires. The one thing I'm worried about with the 4.88 gearing is first and second gear. I'm not worried that they would have enough power, but actually that they have too much power and you have to shift out of them too quickly. I really don't want to pull a left hand turn from a stop light having to shift not only through 2nd gear, but possibly all the way to 3rd gear at the exit of the turn. I watched a video of a guy on-line that showed the difference between his 3.73 gears on 35" tires versus 4.88 gears on 35" tires. It was his first drive after getting 4.88 gearing. It was interesting to hear his surprise at how quickly he had jumped up to 4th gear. It was one of those "oh crap, I didn't expect that, hope I didn't make a mistake" type of reactions.

I think for me, what I'm looking for is that gearing that almost let's me start from a dead stop in 2nd gear. I say almost because I don't want it to be a guarantee in all circumstances, just your usual flat grade, 1/2 second stop with a slow pull out. To me, that would be just about perfect. What I'm basing that on is driving my other vehicles. I've noticed that my other vehicles (all auto's) are calibrated not only in their gearing but also in their programming to actually have you launch in 2nd gear from a stop if the conditions are right. 1st gear is used if it is a full-on stop where you actually sit there for more than 1 second and your previous driving style coming up to the stop sign was more aggressive (because remember, gear programming these days is now adaptive and it knows when you were racing around versus driving like a grandpa.)


i also don't see how you could cruise at 75 mph at 2k rpms. my jeep stock had trouble maintaining 75 because in 6th gear because the RPMs were so low.

I'm not sure about your experience, but as I said above, I was maintaining 40mph at 1400rpm. I used to cruise at 70mph at 2000rpm all the time and it maintained it just fine. The 3.6L has a lot more torque than people give it credit for. I get tired of reading people say all the time that the engine is useless below 1800-1900rpm. That is just crazy! I can accelerate at high speed from 1500rpm!

Timmy
03-26-2015, 01:16 PM
Just another follow-up to the book I just published (sorry, I write a lot.)

For what it's worth, I took a fairly good look at the gearing options from stock, to 35" tires to 37" tires. It is becoming very apparent to me of the following based on RPM vs. MPH vs. Gear (I'm now realizing I'm re-inventing the wheel here, aka, the chart at the beginning of this forum.)

3.6L JK with 6spd Manual (Auto is probably the same.)
3.23 Gearing on stock tires = 3.73 gearing on 35" tires = 4.10 gearing on 37" tires (basically a base JK feel.)
3.73 Gearing on stock tires = 4.10 gearing on 35" tires = 4.56 gearing on 37" tires (basically a JKU with the max tow package feel.)
4.10 Gearing on stock tires = 4.56 gearing on 35" tires = 4.88 gearing on 37" tires (basically a Rubicon feel.)

In each case, the gearing is slightly steeper to the 35" tires, and then slightly steeper yet to the 37" tires. It's not by much, about 1% change for each, but that is enough to possibly make up for the difference of the added weight of the tires.

Maybe the real question we need to be targeting for people is... If you went to a dealer and test drove a base JK, a JKU with the max towing package and a Rubicon, which did you like driving the most?

The little equation I just posted above is basically what the graphical chart at the beginning of this thread shows, I think it just puts it in a little more in-your-face, easier to digest style as you know you could go to a dealer and experience all three to better understand what you could expect from your Jeep after a re-gear.

2k13jk
03-26-2015, 02:13 PM
My 13 jk 6 speed equipped with a ripp i had a buddy slap 4.10s in over my old 3.21s and its a perfeft combo i can use 6th as low as 45mph and still have acceleration power at 70 i doing 2200

JeepLab
03-26-2015, 04:43 PM
anyway a lot of this is circumstantial and i have to agree with snarf, drive what feels best. clearly with your setup 4.56 drives best. it would be very hard to duplicate that as i don't know anyone in person that has a turbo or super charger. and maybe you can get away with 4.56 on 37s BECAUSE of the super charger ... or if you have a free RIPP supercharger i would be happy to be a guinea pig ;)

"Drive what feels best" is no answer at all. Anyone can agree with that. The driver's goals will dictate what feels best, and with gears you rarely know how its going to feel until you've spent the money and ripped your diffs apart.

Im not against 5.13, please dont take it that way, Tonka, our JK on 40s has 5.13 and no SC and she feels fast. there are different opinions with regard to this related to driving style and location. In NJ you want to be able to drive fast as well as wheel. I also have a 4 to 1 transfer case that gives a little more freedom to run a little less gear.

the best information is for those of us who have actually done it to share with others what our trucks do mathematically now. Then others can get in their trucks and run their RPM up to where we say ours go to maintain highway speed, and see if thats livable for them.

Pznivy
03-26-2015, 08:19 PM
I have 5.13s. My 37s measure 35 (KM2) I dont have a rubi, and am not on the highway often. Its the best feeling for my situation, Might be too much gear for others, but when I put it in 4 lo and the truck climbs without me touching the pedals regardless of terrain its worth it.

Shouldnt drive too fast anyway. No rush.

KaiserBill
03-26-2015, 09:15 PM
That is way out of line with BFG's liturature on their tires which states the tires are 36.8 inch in diameter. I cannot see them having a +/- 1.8inches manufacturing tolerance. I could see +/-.30 manufacturing tolerance at most.

dalearyous
03-26-2015, 09:57 PM
3.6L JK with 6spd Manual (Auto is probably the same.)
3.23 Gearing on stock tires = 3.73 gearing on 35" tires = 4.10 gearing on 37" tires (basically a base JK feel.)
3.73 Gearing on stock tires = 4.10 gearing on 35" tires = 4.56 gearing on 37" tires (basically a JKU with the max tow package feel.)
4.10 Gearing on stock tires = 4.56 gearing on 35" tires = 4.88 gearing on 37" tires (basically a Rubicon feel.)


i like this. this is basically how it was described to me.


"Drive what feels best" is no answer at all. Anyone can agree with that. The driver's goals will dictate what feels best, and with gears you rarely know how its going to feel until you've spent the money and ripped your diffs apart.

Im not against 5.13, please dont take it that way, Tonka, our JK on 40s has 5.13 and no SC and she feels fast. there are different opinions with regard to this related to driving style and location. In NJ you want to be able to drive fast as well as wheel. I also have a 4 to 1 transfer case that gives a little more freedom to run a little less gear.

the best information is for those of us who have actually done it to share with others what our trucks do mathematically now. Then others can get in their trucks and run their RPM up to where we say ours go to maintain highway speed, and see if thats livable for them.

"drive what feels best" as in like what was said, try and find and test drive other peoples rigs and then make a decision. i understand and i am not offended at all. your original post was trying to be informative and point out some glaring misinformation that people use to select gears and i agree with it. i also started this late, on my phone, and just now (on my computer) realize what timmy's rig is and that he does not have a SC. :rolleyes: so that explains a bit.

Timmy
03-27-2015, 03:01 PM
Hey guys, I'm ordering my 4.56 gears today and thought I'd post at how I came to my decision on the gear ratio I selected in the event that it helps someone else out (lookin' at you Pickles, for when you finally upgrade to 37" tires, ba hahaha. See Pickles Tire Decision thread for the background here.)

My Jeep: 2014 JKU Sahara, 3.6L manual 6spd, 37" tires. Only future upgrade is a new front bumper and winch (around 200lbs. more weight) and possibly a supercharger if things work out.

First, I'd like to thank some of the forum people here for allowing me to chat with them. I spoke with FerrariFast (FF) and jt1911, who was kind enough to chat with me by phone. Both have rigs with 37" tires, but both were Autos running 4.88 gearing versus my 6spd. Both of the guys love their 4.88 gearing and are recommending I go that direction versus the 4.56 gearing that JL recommends.

What I have been experiencing overall is that the majority of people making recommendations are running auto transmissions and then broadly indicating their experience should translate just fine for people with 6spd's. Then I keep reading and re-reading what JeepLab has said and experienced, and putting much more weight behind his comments because he is running a manual as well. The reality is, the 6spd's do have a different experience because the gearing is different. It's too easy to focus in on the fact that sixth gear in the manual is close to the fifth gear in the auto and call it good from there. Truth be told, the 6spd has steeper gears from 1st-4th, 5th gear is equal to the auto's 4th, and 6th gear is longer than the auto's 5th gear. If I were to match the axle gearing of someone running an auto, I'd find my 1st-4th gears to be shifting much sooner than they are, all in an effort to say that my overdrive gear is now matching that of an auto transmission. To help demonstrate this, here is part of my discussion with FF. He very kindly sent me the following showing when his Jeep was shifting on his way to 60 Mph.



Auto Transmission...

1st gear shifts around 18-20 MPH
2nd gear shifts around 35 MPH
3rd gear shifts around 47 MPH
60 MPH cruising at 2250 RPMs.


I went ahead and whipped up a formula to calculate what speed my manual 6spd would be at if I shifted at the same RPM as FF with 4.88 gearing and then with 4.56 gearing. (Sorry the formula is not more simplified, it is written this way to dump into my programmable calculator.) His auto is shifting around the same time I personally shift (obviously on a 6spd, shift point is unique per person but I do find in every day driving I typically shift around 3000 to 3200 RPM naturally, which matches what his Jeep was doing.)

Formula

MPH = (((([RPM/({Trans Gear Ratio}*{Axle Ratio}))*{Circumference of tire in inches})/12[inches])/5280[feet])*60[minutes]

Example

What speed would I be traveling when at 2250 RPM, in 6th gear, with a 4.88 axle on 37" tires (36" measured)?

61.95 Mph = ((((2250/(.797*4.88))*113.09)/12)/5280)*60

All calculated with 37" tires, accept the stock Rubicon which is calculated with stock tires.
1st Gear @ 3100 RPM (FF's shift point to 2nd gear)

4.88 Axle, Auto [3.59:1] - 19 Mph
4.88 Axle, Manual [4.459:1] - 15 Mph
4.56 Axle, Manual [4.459:1] - 16 Mph
4.10 Axle, Auto Stock Rubicon [3.59:1] - 19 Mph

2nd Gear @ 3500 RPM (FF's shift point to 3rd gear)

4.88 Axle, Auto [2.19:1] - 35 Mph
4.88 Axle, Manual [2.614:1] - 27 Mph
4.56 Axle, Manual [2.614:1] - 29 Mph
4.10 Axle, Auto Stock Rubicon [2.19:1] - 36 Mph

3rd Gear @ 3000 RPM (FF's shift point to 4th gear)

4.88 Axle, Auto [1.41:1] - 47 Mph
4.88 Axle, Manual [1.723:1] - 38 Mph
4.56 Axle, Manual [1.723:1] - 41 Mph
4.10 Axle, Auto Stock Rubicon [1.41:1] - 48 Mph

4th Gear @ 2735 RPM (FF didn't provide this, I'm guessing it held 4th to 60 Mph and then it switched to 5th gear once he lifted.)

4.88 Axle, Auto [1.0:1] - 60 Mph
4.88 Axle, Manual [1.2:1] - 50 Mph
4.56 Axle, Manual [1.2:1] - 54 Mph
4.10 Axle, Auto Stock Rubicon [1.0:1] - 62 Mph

5th Gear @ 2250 RPM (FF's recorded cruise RPM. I also would have held 4th to 60Mph, but I'd skip 5th and go directly to 6th.)

4.88 Axle, Auto [0.83:1] - 60 Mph
4.88 Axle, Manual [1.0:1] - 49 Mph
4.56 Axle, Manual [1.0:1] - 53 Mph
4.10 Axle, Auto Stock Rubicon [0.83:1] - 61 Mph

6th Gear @ 60 Mph (This shows what RPM I would be at in the manual's overdrive gear at 60 Mph, ie. MPG savings!)

4.88 Axle, Manual [0.797:1] - 2180 RPM (vs. 2250 RPM of auto)
4.56 Axle, Manual [0.797:1] - 2037 RPM (vs. 2250 RPM of auto)


Just for comparison, here is how fast the 6spd would have been going if I ran at FF's cruising RPM.
6th Gear @ 2250 RPM

4.88 Axle, Manual [0.797:1] - 62 Mph (vs. 60 Mph of auto)
4.56 Axle, Manual [0.797:1] - 66 Mph (vs. 60 Mph of auto)


I get what JeepLab was describing now about 4.56's being a nice fit for a 6spd manual. If I ran 4.88 gearing on my 6spd, it's not that it would be horrible or anything, but, it certainly is not the same experience as described by those with autos. The 4.56 gearing is ALREADY a steeper gearing overall for the 1st-4th gears than the autos with 4.88 gears! In other words, it already has more power, I'm already shifting sooner/more, let alone what the 4.88 gears would provide vs. an auto. If the 1st-4th gears are already steeper than those happy 4.88 auto guys, than why not go with the 4.56 vs. the 4.88 gearing and pick up some more fuel efficient high end that is also quieter and smoother at highway speeds? The 4.56 gearing in a manual transmission, with 37" tires, is STILL more aggressive/steeper than a stock Rubicon with 4.10 gears of same transmission (6spd or auto!) New Jeep owners are advised all the time that the automatic Rubicon is a better city driver and not as preferred on the highway as a Sahara if it's your daily driver. Dang! And the 4.56 geared 6spd, on 37" tires, is steeper in 1st-4th than a stock automatic Rubicon, but you get a lower overdrive gear (ie. lower final RPM) than a stock Rubicon!

So, long story short, I'm going with the 4.56 gears. Obviously everything I wrote here is "science" and real-life might play out different, but I really think that the experience in a 6spd manual deserves a slightly different decision or approach than that of an automatic. The process of doing this research has also really opened up my eyes about all the different configurations you can purchase a new Jeep and what your experience might be in each combination.

Thanks to everyone for your feedback and lively discussion. I might actually hold off on ordering the gears today if for no other reason that northridge4x4 has Easter Safari kicking off tomorrow, so maybe a deal will come my way ;-) So if you guys look over this and see some error in my work, or decision making, there is still time re-evaluate and make a different decision.

Regards,

Timmy!

Rexx19
03-27-2015, 03:54 PM
The most important difference auto vs. manual, is in the manual, you can pick your gear. Dont have enough gear? down shift. Too much? up shift.

The auto guys are more at the mercy of the mathmatics and gear ratios.

Timmy
03-27-2015, 04:57 PM
The most important difference auto vs. manual, is in the manual, you can pick your gear. Dont have enough gear? down shift. Too much? up shift.

The auto guys are more at the mercy of the mathmatics and gear ratios.

Great point, and one reason why I like the manuals! Not to mention I don't have to mess around with getting the transmission re-programmed when changing tire/gear sizes, or changing again when you put a supercharger in. Plus, you get an extra gear that you can decide how best to use (for re-gearing) as either more low-end, or more-high end fuel savings! There are good reasons to buy an auto, but I think there are better reasons to go manual.

KaiserBill
03-27-2015, 07:22 PM
Technically speaking given the way a torque converter works the automatic guys actually can run their engines at lower rpms without lugging the engine-- where as you in a manual will have to down shift to increase your mechanical advantage. The real advantage comes when you decide to shift when accelerating or decelerating. That's when your manual gearbox really helps out because you'll shift at point when the car or truck feels better then with the automatic. As you you would be at the mercy of the automated system's programmed shift points. Sure most AT's use some form of simplistic adaptive system where they model their shifting behavior based on your throttle inputs-- that doesn't really help too much when do something like change the tires to a size 5 or 6 inches larger than stock. But on the converse the automatic works better at low rpm and gives you a torque boost.

It is also usually nice that manuals have closer ratio spreads and have more gears which helps to make up for things like changing tires or other modifications.

Personally, I prefer the manual gearbox.

dalearyous
03-30-2015, 09:45 AM
timmy, can you break down in percent time spent on driving in the city, highway, trails? i think that is also important when making this decision. also, please post back your impressions once the gears are in (i am sure you will).

did the dana 30 have any weight in your decision (as far as pinion size concerns etc ...)?

Timmy
03-30-2015, 01:22 PM
timmy, can you break down in percent time spent on driving in the city, highway, trails? i think that is also important when making this decision. also, please post back your impressions once the gears are in (i am sure you will).

did the dana 30 have any weight in your decision (as far as pinion size concerns etc ...)?

Oh yeah, sorry, I put this in my "37" tire upgrade" thread and forgot to repost it over here.

Here's my percentage driving
40% - 0mph-40mph
40% - 40mph-60mph
10% - 60mph-80mph (my sedan makes up any other highway driving as needed)
10% - Off-Road (hopefully this number will increase as I learn the area a bit more)

Great question on the Dana 30! Yep, the Dana 30 did actually weigh into the decision slightly. I've read that 4.88 is really the highest gear you can safely go on a Dana 30 from a strength standpoint. There are people running 5.13's on the Dana 30 front without any issue, but I've seen pictures and the pinion gear suuuuuuure looks small. Knowing that I want to put a supercharger on at some point (if I can stop forking out money for other upgrades first!) I wanted to make sure I had a ring/pinion that could handle the added power. If 4.88 is supposedly the highest recommended, I figured backing off to a 4.56 would give me a nice safe margin if/when the engine has a nice big power bump. The gears and labor are expensive enough that I would be pretty pissed off if I went with 4.88's and then put an SC on and found that I broke the pinion due to too much torque. I purchased Yukon gears, which are supposed to be pretty good, but then I read that basically every "good" gear you purchase for a Jeep these days is all manufactured from the same main supplier (whoever that is, and most likely made in China.) So with that information in mind, it also swayed me to 4.56 to make sure the pinion gear was a little larger.

I'm having a hard time finding a pic I've seen of the difference between 4.56, 4.88 and 5.13 pinions. Here is one though that shows the difference between a 3.07 next to a 4.56 Dana 30 pinion, which certainly shows the dramatic difference in size. You can imagine how much smaller a 4.88 and 5.13 would be.

http://i6.photobucket.com/albums/y249/mr5oh/30745635.jpg

Here's a pic of a Dana 44 vs Dana 30 of the same gear gear sizing to see how much smaller a Dana 30 is.
http://www.wranglerforum.com/attachment.php?attachmentid=288095&d=1377020282

Here's a Dana 30 destroyed by 37" tires (not sure what pinion size it was.) The caption of the post was "Yeah, D30 rings and pinions are virtually bullet proof..." (said jokingly in response to someone saying most people don't break D30's.)
http://www.jeepforum.com/forum/attachments/f9/1477330d1405470730t-how-much-tire-can-dana-30-44-combo-handle-35s-37s-no-extreme-offroad-pinion2.jpg

Gunner
04-04-2015, 12:49 PM
I just went from 4.56 on 35's to 37's. Mine is a 13 auto. So far I am happy with the change. My highway rpm is a bit lower for highway cruising which is nice at 75 to 80. As far as on the rocks I really didn't notice any big difference in crawling. I am checking gas milage averages right now. I did the Procal and am checking it against a GPS and some known distances to calibrate it. All in all I am happy with my 37's on 4.56 gears.

Timmy
04-05-2015, 03:41 AM
I just went from 4.56 on 35's to 37's. Mine is a 13 auto. So far I am happy with the change. My highway rpm is a bit lower for highway cruising which is nice at 75 to 80. As far as on the rocks I really didn't notice any big difference in crawling. I am checking gas milage averages right now. I did the Procal and am checking it against a GPS and some known distances to calibrate it. All in all I am happy with my 37's on 4.56 gears.

Sweet Jeep Gunner! Love the color. Glad to hear that you like the 4.56's on 37" tires. My gears finally arrived and I'm scheduled for April 16th for the install. Feels like I'm waiting forever to get these gears in!!! With the 35" tires and the 3.73 gears, the Jeep was drivable and fun. Going to 37" tires, it's still drivable, but it's lost some of the fun factor. I'm having to balance the clutch/gas a lot more, which takes the fun out of it.

Took it off-road this weekend. Stuff the right rear 37" tire and of course it rubbed on the fender ;-) The need for upgrades never stops. Can't believe the price these manufacturers want for flat fenders. I'm toying with the idea of going the cheap route and cutting the stock fenders, then I can also get the shape I want. I figure if I cut them and don't like them, I can pick up lightly used ones on Craigslist for dirt cheap and try again. Naturally I was looking at your flat fenders on your Jeep!

Gunner
04-06-2015, 03:53 PM
Yes they do cost. But I ended up resting on 2 wheels and my right rear fender on this little spot. All I got was some rash on the fender lip. If I had not had a good solid fender on it I would have banged up a door like my buddy did on the jeep right behind me. It was well worth the bucks.

Timmy
04-18-2015, 12:11 AM
Got my new gears installed finally (4.56.) So far, I'm very happy with them. I think 4.56 on 37" match pretty well to the feel of a stock wrangler with the tow package (ie. 3.73 gearing.) I do think that I could have gone with 4.88 gears and I would have been just as happy. I've got a set of 35" studded duratrac tires I run in the winter, so the 4.56 gears will probably work better with the smaller winter tires than what the 4.88 would have.

Gas mileage on the way home from the shop was round 19mpg at around 60mph. I was able to cruise in 6th gear at 60mph with some slight hills and it still had enough power for the cruise to handle it, but it's still tall enough that I'm right at 2k RPM @ 60mph and getting good gas mileage.

Just removed the OEM front bumper tonight, the new ARB bumper and winch is going on tomorrow! Temps are forecast at 70 degrees this next week, so it just might be time to go into summer-time mode and get the doors and top off!

JeepLab
04-18-2015, 01:36 PM
Got my new gears installed finally (4.56.) So far, I'm very happy with them. I think 4.56 on 37" match pretty well to the feel of a stock wrangler with the tow package (ie. 3.73 gearing.) I do think that I could have gone with 4.88 gears and I would have been just as happy. I've got a set of 35" studded duratrac tires I run in the winter, so the 4.56 gears will probably work better with the smaller winter tires than what the 4.88 would have.

Gas mileage on the way home from the shop was round 19mpg at around 60mph. I was able to cruise in 6th gear at 60mph with some slight hills and it still had enough power for the cruise to handle it, but it's still tall enough that I'm right at 2k RPM @ 60mph and getting good gas mileage.

Just removed the OEM front bumper tonight, the new ARB bumper and winch is going on tomorrow! Temps are forecast at 70 degrees this next week, so it just might be time to go into summer-time mode and get the doors and top off!

The difference between 4.56 and 4.88 is bigger than you think. You made the right choice ESPECIALLY if you want to run duratracs.

JJeep
09-15-2016, 07:29 AM
I recently bought a 2016 Unlimited, auto-trans. I am having 3.5 superflex lift installed with 37" Toyo MTs. Were you saying that the two members that drove the autos preferred the 4.88 to the 4.56. Thanks. There is just so many different opinions and "experts" on regearing.

JeepLab
09-16-2016, 09:02 AM
I recently bought a 2016 Unlimited, auto-trans. I am having 3.5 superflex lift installed with 37" Toyo MTs. Were you saying that the two members that drove the autos preferred the 4.88 to the 4.56. Thanks. There is just so many different opinions and "experts" on regearing.

Where do you live? mountains? or highways?

If you want to keep your truck a good highway cruiser, go 4.56. If you are looking for maximum crawl, 4.88.

I had 4.88s, and it was too much gear for me as a daily driver. Turned a rocket into a pig. (well not really, but bad enough to change again)

What are your current gears?

Timmy
09-17-2016, 03:11 PM
I recently bought a 2016 Unlimited, auto-trans. I am having 3.5 superflex lift installed with 37" Toyo MTs. Were you saying that the two members that drove the autos preferred the 4.88 to the 4.56. Thanks. There is just so many different opinions and "experts" on regearing.

I have 37" tires and a manual trans. Technically the manual trans is providing a hair bit lower gearing than the auto so my experience may not match yours. I actually have the opposite view of Ross. I put in 4.56 gears and after having it for about a year I wish I would have put in 4.88. I often find that the gearing is just not low enough for all types of driving, city and highway. Sometimes I burn the clutch in reverse if I have to get over/up something big because it's just not enough. On the highway, I hardly ever shift into 6th gear because it just can't handle it. I only shift into 6th gear when I'm over 60 mph. I may use 6th gear at 50mph, but only if the road is totally flat or downhill.

I drove from WA to Lake Powell in Arizona by way of Montana, Idaho and then Utah. Coming in to Utah I was sucking eggs. We were about 6,500 elevation before heading in to Arizona and we had a lot of ups and downs on the Interstate. The Jeep topped out at 85mph and I couldn't go any faster, that was flat out all she had in sixth gear. Going up hill, if I even wanted to maintain 80mph, I had to draft behind a larger vehicle and drop down a gear a two. I was really wishing I had just a few more hundred RPM in sixth gear to help maintain the highways speeds as I was dropping down to 5th gear all the time. I honestly didn't see any better gas mileage in 6th gear vs. 5th.

I do know that Ross has a supercharger in his rig, and it was a manual like mine. With a supercharger, the 3.56 might be perfect, but I really think that without one you need to go 4.88. Instead of switching out my gear, I'd rather the $2k go in to a supercharger and see if I can't solve my situation with more power ;-)

Like I said, if I had to do it all over again, I would go 4.88.

Hope that helps muddy the water for you!


[UPDATE: Durp... forget to mention I had a kayak and two paddle boards on my roof to Lake Powell, so that just added to the aerodynamics of my already streamlined brick on the Interstate.]

JeepLab
09-17-2016, 03:35 PM
I have 37" tires and a manual trans. Technically the manual trans is providing a hair bit lower gearing than the auto so my experience may not match yours. I actually have the opposite view of Ross. I put in 4.56 gears and after having it for about a year I wish I would have put in 4.88. I often find that the gearing is just not low enough for all types of driving, city and highway. Sometimes I burn the clutch in reverse if I have to get over/up something big because it's just not enough. On the highway, I hardly ever shift into 6th gear because it just can't handle it. I only shift into 6th gear when I'm over 60 mph. I may use 6th gear at 50mph, but only if the road is totally flat or downhill.

I drove from WA to Lake Powell in Arizona by way of Montana, Idaho and then Utah. Coming in to Utah I was sucking eggs. We were about 6,500 elevation before heading in to Arizona and we had a lot of ups and downs on the Interstate. The Jeep topped out at 85mph and I couldn't go any faster, that was flat out all she had in sixth gear. Going up hill, if I even wanted to maintain 80mph, I had to draft behind a larger vehicle and drop down a gear a two. I was really wishing I had just a few more hundred RPM in sixth gear to help maintain the highways speeds as I was dropping down to 5th gear all the time. I honestly didn't see any better gas mileage in 6th gear vs. 5th.

I do know that Ross has a supercharger in his rig, and it was a manual like mine. With a supercharger, the 3.56 might be perfect, but I really think that without one you need to go 4.88. Instead of switching out my gear, I'd rather the $2k go in to a supercharger and see if I can't solve my situation with more power ;-)

Like I said, if I had to do it all over again, I would go 4.88.

Hope that helps muddy the water for you!


[UPDATE: Durp... forget to mention I had a kayak and two paddle boards on my roof to Lake Powell, so that just added to the aerodynamics of my already streamlined brick on the Interstate.]


OMG TIMMY! Did I screw you? You followed my lead on 4.56 and regret it? That hurts me to my core.

I see no way that it could be the wrong decision for highway driving like you are talking about, but wouldnt disagree with your experience.

How heavy is your rig? lots of steel? maybe thats the difference?

Timmy
09-19-2016, 10:02 AM
OMG TIMMY! Did I screw you? You followed my lead on 4.56 and regret it? That hurts me to my core.

I see no way that it could be the wrong decision for highway driving like you are talking about, but wouldn't disagree with your experience.

How heavy is your rig? lots of steel? maybe thats the difference?

Oh man, don't sweat it for a second. I researched a ton from a lot of different resources. One of the reasons I picked the 4.56 is that I felt if I erred in my decision, I would rather error too low than too high as us manual guys can always just down shift if you error low ;-) Also, I was always planning on going with a supercharger and I suspected that your own preference between the two gears was because of your supercharger. I didn't want to buy 4.88's and then toss in a supercharger and wish I had put the 4.56's in. I'd rather have the 4.56's and wish I had a supercharger and move that direction. Sadly, my damn family keeps sucking away all my fun money (haha!)

As for heavy... Compared to yours, yeah I'd be heavier. My Toyo's are heavier than your tires and I also have a full width front and rear ARB bumper. Everything else is pretty well stock so it shouldn't be much more than say 150lbs though. I can easily make that up by taking my top and doors off (which I do all summer) but even with that weight off the 4.56's are still just not enough.