siaby

So I'm planning on regearing my 13 unlimited sport w/ auto transmission, and I've called a few shops and the majority recommend 4.88 ratio for the 37's I'm planning on running. But on these boards I keep reading 5.13. These shops have been recommended by fellow jeepers. Now I'm confused.

Tooadvanced

I don't have 37's but I would say 4.88 r more than enough. There r quite a few folks with 4.10 on 37's that r happy. 4.56 is even in the performace range with 37s

jnabird333

If you do a lot of highway and you want to go fast 4.88s. If your focus is more trail and are willing to slow down a bit on the highway, then absolutely go with 5.13s

4.88s on 37s mathmatically are closer to the stock 4.10 on 32" tires but the 37s require more torque to overcome the inertia of the larger tire mass. So you need the higher (numerical) gear to overcome this and return "stock" performance.

I would go (and have gone) 5.13s on 37s. Our other Jeep has 4.88s on 35s.

jeep-rat

I went 4.88 on my 13 with 37s. Perfect in my opinion. If you do much highway, 5.13 would be too much.

mattgt5

Sorry to offer the other side but I did not like 4.88 on 37" in my 13 jkur. Too high on the rpm on the highway. I liked my 4.10 better. 4.56 May have been perfect for me but didn't want to pay that much cash for a small change. I live on the coast for topographical reference.

sent from my work leash

nthinuf

There can be differences in gearing needs between the 3.8 and the 3.6 engines. And between auto's and manuals. 2 and 4 door. Elevation and sea level. Flat roads and lots of hills. Mainly high speed freeway and mostly in town or offroad. And then you get people jumping into threads for one engine giving their advice based on the other, or based on the other transmission, or completely different location or use. It is no surprise that you might be confused...

siaby

Thanks for the replies, well my jeep is a daily driver that see's a lot of freeway and not much trails so I'm leaning towards the 4.88. Hope I'm right

nthinuf

Stuck right to the top of this modified area are some FAQ's. If you open them and scroll down (the links are probably still broken, so just scroll down) you will find some good rpm charts divided by engine and transmission. Use actual measured tire height, not mfg spec.

These charts don't take a lot of the variables into account, but are a decent resource for a base rpm at 70 mph.

TURTLECON

I've got 5.13s on my 2013 with 37s. Great for off road, not so great for fast highway. I slightly regret not going 4.88s, but I can live with it. I'm right around 2800rpm at 70mph and I don't average faster than that because of the gearing.

siaby

Thanks freak I'm going with 4.88