I just had my gears swapped from 3.21s to 4.88s I'm currently running 33" tires. I went with this ratio figuring I would go to 35" tires when the time comes. (in about 20,000 miles) The difference is amazing! however my rpms at 65mph went from 2200rpm in 5th gear to 2800rpm in 6th gear. Will running the engine at these high rpms cause any undue ware or be bad for the engine in any way? I travel about 80 miles a day at this speed. Any input would be appreciated.

 

Nope, you should be fine. The JK's seem to like the higher RPMs anyway. You've got nothing to worry about. Just enjoy your JK

 

The JK seems to get the best mpg at about 2200-2400 rpms. Thats a lot of gear for 33s, almost too much for 35s with the 6spd.

Get the 35s.

 

I am think about doing the same thing. Did you go to a local shop? How much did it cost? Also, since I am a total newbie, do I only need to do the gears in the back and not in the front differential, or do I need to do both?

 

both if its a 4wd

 

That's about what I was getting with the stock tires (245 75 16s) and 4:10's. You'll be fine, but your gas mileage will go down. That's awesome gearing for power and towing though. It'll be right where you want it when you get those 35's.

 

you should be ok. i just checked mine to see how the rpm's compare. at 60-70 mph my rpm's were 2300-2600 but i have an auto, 33's, and 4:10. i talked to the dealer about gearing and they said the jk will have a higher rpm range then previous jeeps. so that sound about right. you should go with the 35's for optimum performance.

 

price?????

 

did you have to change front carrier

 

$1200 gears and labor
Yes I did but only because I went from 3.21s. The carrier from the 4.10s is the correct carrier and you would not need to change it.

Thanks for all the input guys! I feel a lot better about my decision to to go with 4.88s now I just have to wear out my 33s so I can get those 35s