New Gears for XJ?

[Rudeboyrob88]

Has anyone on here regeared their XJ after putting bigger tires on? I have an '01 XJ sport with a 4" lift, and I just got 31 x 12.50's. After my first full week of driving it, I am noticing that it struggles at higher speeds on the highway. I was wondering what a better gear setting would be, and where I might be able to get that done. Also if you have an idea of how expensive somehting like this might be. Whatever comments, or suggestions you can offer would be appreciated.

[Dukes69]

It all depends on where you want to go with your Jeep. I would suggest you sit down and figure that out. If you have to regear at every step you take, you will be broke. If you plan on going to 33's and stopping there, then regear for 33's. Just MHO.

[jmbrowning]

4.10 for 31's
4.56 for 33's (what the Missus is running on her XJ).

[Rudeboyrob88]

Another question;

I am new to building up a jeep, so bare with me. I hope this is not a dumb question, but when regearing, do you need to do the front and the back? Or does it matter? I would think that 4-wheel drive would be a little weird with stock gears in the front, and new ones in the back. Just curious.

[shortbus]

Mismatched gears would cause a lot of undue stress on the transfer case, and likely cause failure.

The only stupid question is the one left unasked.

[Dukes69]

I can almost guaruntee failure. with a parttime t-case the front and rear driveshafts turn at the same rate. if you have 4.56 gears in the rear and 3.55's in the front (for example). The rear drive shaft needs to spin 4.56 times for the tires to turn once. the front needs 3.55 times to turn once. With traction you a binding the hell out of everything and something has to give. Now, you can do the rear then do the fronts a month later if you dont use 4wd. Also, for reference you dont have to use the exact ratio front and rear, they can be like 3% off. So 4.10 and 4.11's would be ok.

[Rudeboyrob88]

Thank you, This is very helpful. Now I just need to get some estimates. This is probably my next big upgrade.

[JeepJunkie]

Also, for reference you dont have to use the exact ratio front and rear, they can be like 3% off. So 4.10 and 4.11's would be ok.

This would only be if they didnt make the same gear ratio for your axles right and thats as close as you can get?

[Dukes69]

This would only be if they didnt make the same gear ratio for your axles right and thats as close as you can get?

correct

[Elusive]

I shot you a PM