The Truth about Gears and Tires

[JJeep]

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]

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]

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]

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]

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.

[Rexx19]

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]

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]

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]

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]

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.



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.


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.)