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Regearing to 4.88 with 35" tires- did I mess up?!

42K views 50 replies 25 participants last post by  2rad4u 
#1 ·
2013 jeep Sahara with auto 3.21s... Just bought 4.88 gears and now I'm being told I'll be over geared for highway driving? Someone help me cut through the noise!
 
#2 ·
If you are still using the same tires before / after the upgrade and if this is the only change made you will run about 52% higher rpm at the same road speed in the same gear. So if you were running 2000 rpm at 60 mph you would now run 3040 rpm.
 
#3 ·
Not even close to being true.

See below gear chart for approx @ 70 Mph

 
#4 ·
I should add I'm running 295/70/17 nitro trail grapplers today and will be switching to 315/70/17's with the new gears. My concern is I don't want to run into issues with highway driving and running too high RPMs. Lots of conflicting opinions!
 
#9 ·
Dude, relax. I have thousands of miles on my 4.88s (manual) on 35s. The engine is capable of 6400rpm. 3k isn't going to hurt it. All that is going to suck is your gas mileage. Besides... The 4.88s are awesome for 35s. Lots spunkier.
 
#10 ·
3.6 engine with 35's, the optimum is the 4.56 Ratio.
Since you are re-gearing from the 3.21 Ratio, then you will also need a front carrier..FYI
 
#12 ·
That's for an automatic. And no, I have the stock carrier in my D30 up front with 4.88s.
(Granted, going to a PR44 in a few months...)
 
#15 ·
If you live in Kansas, 4.56 might be enough for 35s. If you live anywhere else, I would highly recommend 4.88. Everyone I know have 4.88s and 35s and are happy. Most are also daily drivers.

Things to keep in mind.... When you go to a larger tire size, you are also adding substantial rotating mass, take more power just to spin the tires. So you need a little more gear to compensate for this performance wise. Then, in most cases when you go to a larger tire size, you also just raised your vehicle or put on a leveling kit, taking the rake out of the suspension and further reducing the arrowdynamics of the jeep increasing drag.

IMO, our jeeps start out grossly under powered and have never heard anyone complain about going too low on gearing.

Just my 2 cents. If your happy, we're all happy...
 
#19 ·
If you live in Kansas, 4.56 might be enough for 35s. If you live anywhere else, I would highly recommend 4.88. Everyone I know have 4.88s and 35s and are happy. Most are also daily drivers. Things to keep in mind.... When you go to a larger tire size, you are also adding substantial rotating mass, take more power just to spin the tires. So you need a little more gear to compensate for this performance wise. Then, in most cases when you go to a larger tire size, you also just raised your vehicle or put on a leveling kit, taking the rake out of the suspension and further reducing the arrowdynamics of the jeep increasing drag. IMO, our jeeps start out grossly under powered and have never heard anyone complain about going too low on gearing. Just my 2 cents. If your happy, we're all happy...
Thanks. I'm going to talk to the shop doing the installation for me and see what their opinion is. I'm very on the fence. I like the idea of having the extra power, but would hate to go 4.88 and be stressing the motor at highway speed driving 80 miles/day to work. That being said I feel like if im going through a re gear I only want to do it once and I want to do it right and am worried I might regret 4.56s. Jeep problems...
 
#18 ·
Another route to consider - given your highway driving concerns - is changing out the 2.72:1 transfer case for a 4:1 from a Rubicon and leaving the differentials alone.

*Using the "Gear Calculator" at
Jeep Ratio Calculators

33.25" tire, 3.21 diff & 2.72:1 trans case = 31.35:1 crawl ratio = 6.3mph @ 2000 rpm
34.36" tire, 4.88 diff & 2.72:1 trans case = 47.65:1 crawl ratio = 4.3mph @ 2000 rpm
34.36" tire, 3.21 diff & 4:1 trans case = 46.1:1 crawl ratio = 4.4mph @ 2000 rpm

* these are done assuming 1st gear in an auto tranny and the theoretical tire sizes I calculated earlier
 
#22 ·
Nature of these forums, most people will tell you: "what I have is the best setup . . ".

Weed those people out and take valuable info from those that have no agenda other than providing help. Those guys/gals are pretty easy to spot here and I've learned a lot on from them.

One of the best write ups on gearing I've read so far:
The Truth about Gears and Tires

Good luck with your decision. This stuff can drive you nuts!
 
#23 ·
4.56 is probably fine for most applications. If you're doing the lift for looks, its OK.
Add armor, gear, heavier this and that.. I've got almost an extra 1,000lbs on my JKU. Lower gears help significantly. JCDriller was right on the mark that those calculators and sheets don't take weight into the equation. Hell, I was doing 60mph uphill in 4th @ 4500rpm or so because I had a 40 mph headwind going uphill. Those sheets work great in a vacuum.

Btw, jcdriller has an automatic transmission
 
#27 ·
Using GPS speed. My speedo is a little off; haven't purchased a programmer.
 
#28 ·
I'm at about 2900RPM @70MPH with my 4.88s and 35s .. Could not be happier.. The engine is not 'strained' at all, but it does get a little strain'ee at 80MPH..
Since I have a manual and I try to do a lot of rocks and steep hills, the 4.88s are perfect.

If you have an automatic and/or don't do difficult off-road stuff a lot, then 4.56 might be better for you.
 
#33 ·
So I've decided to go the 4.56 route as I do a lot of highway driving at 60+mph. I recently looked at my build sheet and it states that I have the limited slip rear axle. I believe they are 3.21 gears however. When I orders the new 4.56 gears I didn't realize I had the limited slip rear. Does the limited slip affect me dropping in new 4.56 gears?
 
#39 ·
I will say no you didn't mess up! I have 4.88' in a 2012 6 speed. I can easily cruise highway speeds and the rpm's are not too high nor is the engine working too hard. I mostly wheel and do in town putting around but have also logged enough highway miles to give an experienced answer to you
 
#40 ·
For what it's worth, I enjoy my 3.21s with 35s. I live in flatlands Toronto, Canada and I love maintaining 1500-1600 RPM cruising at 100 km/h (60 mph). I recently did a 200 km round trip mostly highway and I averaged at 11L/100km which translates to about 21 MPG, and that's in below freezing winter conditions with the stingy winter gas mixture. I could not imagine running 4.56 ratio let alone 4.88 but this is just totally subjective.
 
#48 ·
I have an 08 with 4.88s on 35s and will also have a 16 shortly on the same set up. Both manual. Can't wait to compare.
 
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