Mwsubway

Talked with the guy at my local four-wheel-drive shop and he said he would go with 5.38 gear 35 inch tires with anticipation of going to 37 inch tires? I'm not sure I'm convinced, need some input!!!!

scubatech

With the A580 transmission you have you won't need 5.38 gears. I would say 4.88 would be more logical and have a good RPM for the highway.

highoctane

I 2nd that. If you had a 3.8/42RLE engine/trans, then yes 5.38 is what I'd go with. Some people still assume that is true with the '12 and up JK with the 3.6. On the 3.6/W5A580 engine/trans, I'd only go 5.38 gears with 40" tires. With 35s and a plan to eventually move up to 37s I'd go with 4.88.

Mwsubway

Well he said 5.13 would be good but I'd still wish I went with 5.38, so he's ordered already! I hope I won't regret!,,,,

highoctane

5.13 will have your engine rpms just shy of 3k rpm at 70mph on the highway. But once you upgrade to 37s it'll drop the rpms down about 200rpm. With 5.38s and 35s you'd be over 3000 at 70.

Cats&Jeeps

Have had 538's for over 5 years after starting with 488's... Would never go back especially with an automatic and the deep overdrive. Granted mine is 2008 with the anemic 3.8, but nothing beats mechanical advantage with 6 cylinder... Remember the original jeep had a small 4 cylinder 78hp i think with 33's and 538's... It would go anywhere and pull anything... Mechanical advantage!

Might run a higher rpms at 70, but no higher than the manual guys... We seem to forget that when considering automatic re-gear options IMO!

Jeepstercanada

With
The 3.6 you only need 4.88 when you go to 37's. Guy in my local club running 37 and 4.88 he loves it great power

highoctane

The big difference between your jeep with the 42RLE trans and a 3.6 jk with the A580 is the large difference in the overdrive ratio. The A580 is very close to the 6 speed manual where the 42rle is geared very tall, and only has 4 gears.

Mwsubway

Well that's what the guy at shop keeps telling me, that it has that deep over drive and it will be fine! He said he has 5.13 in his but wishes he had 5.38! Don't have any problems with twisting shafts off do you?

falcon241073

Mine is a 3.6 with a manual. I know it's not the same but... I have 4.88 gears and just put on 37" tires. I'm running about 2500 rpm at 70mph. I was running 2700-2750 with 35" tires. I have no issues in the trails or street. First gear is really short. I barely get my foot off the clutch and I'm shifting to second. The gear charts seem to be close. I have been told many times, even by my fab guy, that auto will do fine at the same gears as manual but the general rule of thumb is one step higher numerically in diff gears for auto. So I'd say 4.88 or 5.13.

Ask to drive your mechanics jeep or go for a ride. Get it to 70 and cruise it for a few miles. See what you think.