The 4.56 gearing is growing on me. The SC has some extra zing around town. and still cruises fast on the highway.
The 4.56 gearing is growing on me. The SC has some extra zing around town. and still cruises fast on the highway.
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.
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
4.88
Last edited by Timmy; 03-23-2015 at 09:54 PM.
2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.
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 ;-(
2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.
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.
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.
2014 Jeep JKU Sahara, Manual - /OlllllllO\ - 4" Metal Cloak lift, 37" Toyo Open Country's on 20" XD Bully Rims, 4.56 Yukon gears, Mopar High Top Fenders, ARB Front Bull Bar Bumper, ARB Rear Bumper, Teraflex HD Tire Carrier, Teraflex Tire Carrier Accessory Mount, Twin Rotopax mount, Hi-Lift Jack mounted on front bumper, Reverse LED work lights, Warn 9.5ti winch, Synergy Drag Link, Trackbar Relocation Bracket, AMP Power Steps, JK1001 Radio, SpiderShade.
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.
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