Here is lay out. 98XJ 4.0L, auto, np231, D30, 8.25, stock 3.55 and 31's on RE3.5. I'mn regearing and dont know witch way to go? I would like to maintain 70 mph and not going over 3000rpms what's your thoughts, I will be going to 32 or 33's but my 31's are brand new.

 

on a dd thats not going to be a trail rig 4:10 is fine. if you like to wheel a lot then 4:56

 

4.10 and 33"s is still a smidgen lower than 3.55 and 225/75/15 so i would go 4.10 cause its a little lower than stock on 31's and not over kill.

swap can be done cheaper by just buying jy axles with 4.10s and keeping yours for spare parts. I found new axles cheaper than regearing.

4.10 is my vote. I don't think youll be dissapointed with either though

 

I agree with 4.10s as its what I've got on my truck, and I really like it.

But I'm not sure I'd suggest doing an entire axle swap to accomplish this.

You may be able to get the parts for cheaper, but thats quite a bit of work for changing gear ratios.

 

I'm running 4.10's and 31's. Need 32's or 33's to keep your rpms down lower..

 

I juggled this for weeks and finally went with 4.56's

75mph @ 3250 rpm
70mph @ 3000 rpm
65mph @ 2750rpm

on 32x11.50R15's with room to go to 33's without power loss
takes hills at 80 with no problem
GO 4.56's!!!

 

i dunno, neither way is wrong its just opinion.

I got a d30 and a 29spline 8.25 with 4.10s from the JY for $150 each. Rear is 4 u-joint bolts, 2 shock bolts, 4 u-bolts, and a brake line. Front is 4 control arms, a track bar, 2 TREs, and 2 brake lines. Then you have 2 entire axes worth of spare parts, shafts, wheel bearings, knuckles rotors, ect ect (test stand for rear disk conversion or wj knuckle swap to eliminate down time)

or you could spend 4-500 on gears and bearings, and 4-5 hours each installing the gears. Sure its new stuff, but no spares, it takes more time, and cost more. Assuming your JYs are kinda like mine

this logic only applies if your rocking open or lunch box though, if your adding a carrier case anyways then you need to set up the gears and an axle swap is just dumb

 

i got 32X11.50s with 4.10s super drivable.i love em...these 6cyls are happier at lower rpms..$0.02

 

If you're going 33' s soon then is suggest 4.56's.

If it will be a while then go to 410's,