4.88 or 5.13 gears on 37 inch tires?

ERAUGrad04

New member
That's definitely true. It's not the whole picture, but the chart is a great place to start and does get very close. The chart doesn't reference tire pressures either, which will also change your rolling resistance. That being said, if your running 3000 rpm at 60 mph with 37s and 5.13 gears in a 3.6L, something is seriously wrong.

Is there really enough difference in mass between the different selection of 37" tires and different wheel combos to change the rolling RPM at 70mph by some huge margin? I would think it would only change within some small percentage. I'm not a tire and wheel mass expert but I did stay at a Holiday Inn Express on more than one occasion. ;)

Staying at a Holiday Inn Express is always worth something! :thumb::D

You'd be surprised at the weight of some of these tire/wheel combos. For example, a 37" Nitto Trail Grappler weighs in at 84lbs while a BFG MT is 71lbs. In tire weight, that is 13lbs or 18% heavier. For wheel comparison, an AEV Pinter weighs 27lbs compared to a Slab at 34lbs.

If you swing to the extremes here, a Nitto mounted to the Slab weights 118lbs while the BFG/Pintler combo is 98lbs. That's a difference of 20lbs and nearly 21%.

Not only does your powertrain have to overcome the loss of mechanical advantage of the 37" tire, it also has to get it moving. If you were to mount both of these tire/wheel combos to a low resistance spindle (kinda like a Price-is-Right wheel!) side by side and give each one a spin, that extra 20lbs would be quite noticeable and would require a bit more umph to get going.
 

MR.Ty

Token East Coast Guy
Probably a silly question but does anyone know if the above gearing chart represents advertised or actual tire size?
 

ERAUGrad04

New member
Probably a silly question but does anyone know if the above gearing chart represents advertised or actual tire size?

I think I remember hearing advertised size. I am turning just slightly higher than the chart data at 2800rpms w/37s and 5.13s.
 

dalearyous

New member
i have a '13 JKUR manual with 35 nitto trail grapplers. i have over 1k miles on my Yukon 5.13s. i will be going to 37s as soon as the 35s wear out which is why i chose 5.13s. but honestly, with a manual, 5.13s is perfectly doable on 35s as well. 4 low 1st cannot be stopped! no regrets and i cannot wait for 37s. like many, while axles were down i did the full artec armor kit for the front axle with synergy ball joints and did trusset on the rear with ARB diff covers.
 

USMCvet

Banned
I've got a '15 JKUR and just installed axle assemblies with 5:13's and I'm running 37" MT/R's. At 70 mph I'm turning around 2650 RPM and I'm good with that. Most of my driving is very rural anyhow, or towing a fishing boat. If I have to go to town I've got to cross a mountain pass and I have no down shifting issues with the auto.
 

Exodus 4x4

New member
I've got a '15 JKUR and just installed axle assemblies with 5:13's and I'm running 37" MT/R's. At 70 mph I'm turning around 2650 RPM and I'm good with that. Most of my driving is very rural anyhow, or towing a fishing boat. If I have to go to town I've got to cross a mountain pass and I have no down shifting issues with the auto.

When you say you have no down shifting issues, what do you mean exactly? It doesn't down shift as much or not at all?

I live in a flatter part of Texas, but when I get into the hill country I'm down shifting into 3rd at every hill. I'm definitely re-gearing now but can't decide if I should go with 4.88 or 5.13. I run cooper 35's on my auto JKUR and don't anticipate going bigger. I also don't ever see myself getting into any crawling that would be so extreme that the difference between the 2 would be noticeable.
 

JRied

New member
Can 5.13 go in a front D30? I'm new go easy on me. Prorock44 is a 2 years away honestly unless I break it
 

Hammerman

New member
I'm running 37 in (36.8in new) on my 2008 2dr JK Rubicon with 4.88 gears. along with manual transmission, at 65 mph 2500 rpm . That combination has worked out well.
 
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