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View Full Version : 3.07's with 235/75/15 or 30" tires


clunk
February 8th, 2012, 13:20
My 2000 XJ has the NV3550 5spd and 3.07 axle gears. I need to upgrade the tires in a few months and would like to run a LT235/75/15 tire with a 2" budget boost. I also have a set of all terrains that measure 30x10.5 which I could use in the interim, thus saving me the cost of buying new tires until these wear out.

The difference between the 235/75/15's and the 30x10.5's that I have now is around an inch in both width and height. I'm ready to accept some performance loss from larger tires but will the 235/75/15 really be that much better than the 30x10.5's with my gearing? My engine is strong at only 105k and the NV3550 has a lower 1st gear than the AX-15 so starting might not be as bad, but maybe this is just wishful thinking.

My engine pulls well in every gear with the stock 225/75/15's but 5th is not used much on the long mountain passes around here so I end up winding 2500RPM in 4th. By my calculations the bigger tires would drop RPM's a little and might actually make 4th gear up hills more enjoyable (right now I can watch my gas gauge drop in that RPM range).

Any comments or opinions? The long term plan is to run a 235/75/15 tire like a Duratrac - I've found to be this size ideal for all my DD jeeps. Is there going to be much of a difference between the two tire sizes with my gearing?

This is what the tires look like next to the stock 225/75/15
http://i51.photobucket.com/albums/f398/jbarilwalker/IMG_1908.jpg

xj_maniac_newb
February 8th, 2012, 14:59
I think you will be fine. I'm running 31's on my 4 banger with the stock 4:10's and it's alright.

Ivan
February 8th, 2012, 16:39
With my 5spd / AX15, I had 3.07's and 30's for a short while. It drove rather "meh", as it felt sort of gutless. Hills were sucky, and I was always downshifting. Driving in 5th gear started to get decent at around 70 mph, but 5th gear was pretty useless below that except for down hills. I've since moved up to 32's with 4.56's and love it!

If you are set in sticking with a 30" tire, then I would recommend going to 4.10's to make your life easier. Correct gearing makes all the difference in the world on how well your rig performs.

foxwar71
February 8th, 2012, 17:10
With the little deeper 1st and little higher OD of the 3550 over the AX15, I think the 3.07's won't be too bad. I've got an 4.0/AX15/242 and 3.55 axles. I ran 225/75/15's with it at first, over like 65mph it would whine out the eninge pretty good. It still got pretty great mileage, could cruise around town in 5th no problem, very response. I got undersized 31's and now true 31's on it. It does good and drive like a stock setup, the jeep is no dog even with some extra fat on it. I can still get low 20 mpg's outta it too.

You say you gotta deal with some hills and such, think about swapping in some axles outta an auto XJ so the jeep will pull more effiecently. I'd love to swap a 3550 into my jeep if the AX15 ever dies.

clunk
February 8th, 2012, 17:45
Thanks for the input guys. I hadn't realized that the NV3550 has a deeper 5th gear as well.

The end goal with this XJ is only a 235/75/15 tire (I'm even having a hard time justifying a small 2" lift) so I don't plan on regearing for such a small increase in size. I've owned bigger 4x4's over the years but a stock or near stock XJ with decent tires gets me where I need to go so I've decided to keep this one nice and clean as a daily driver/weekend explorer.

Johnnie Walker
February 9th, 2012, 11:02
You will be fine with 30's if you want. 235/75 will be better. And really, if you can get a pair of Axles from an auto XJ for cheap, it would be worth it IMO. But the choice is yours.

VAhasnoWAVES
February 9th, 2012, 11:38
lower first gear isnt going to do you a ton... its the higher gears where you will see performance loss.

ive ran 30x9.50s and 31x10.50s behind my AX15 (3.07s as well)... i really cant compare the 30s well, because that was also behind a stroker. but the 31s behind a stock 4.0 sucked. i saw increased performance when i stopped using 5th gear.

if youve got the time and intend to keep the jeep low, install some 3.55 geared axles. youll like the feel.

clunk
February 9th, 2012, 11:49
Well, I'm going to install the 30x10.5's I have once the snow melts and see how she goes. My commute is only 10 miles at 60mph and a little city driving so I'm sure I can suck it up for 6 months until these tires wear out and I decide what my next step will be.

A few years down the road I'd like to see the jeep on 33x10.5's and 4.56's but that won't happen for quite some time, so in the interim I just plan on keeping it low and little.

JEEPS
February 9th, 2012, 17:16
I wouldn't worry, I have two late model XJs with the NV3550 and have driven them from stock to where they sit now with 32" tires. Even with a 30" tire, your NV3550 with the lower RPM peak torque output compared with some of the mid 90s and earlier AX15s and 4.0s, (that I also owned a few of) the difference between the gearing is definitely going to help you quite a bit. The lower 1st is what I love the most since highway hasn't been an issue.

I run 3.55 gears on my '01 4.0 5sp with 32" tires all over the streets and highways and I never have to down shift for hills or have issues with starting off.

I run 3.73 gears on my '00 wheeling rig with 32" tires because it does help in the rocks.

I have wheeled 32s with the 3.07s and it was plenty doable but I don't hate my clutch that much. On the road it wasn't too bad but I could feel it in the hills and taking off from a stop never felt right.

Hope this helped,

Brian

Eric96Xj
February 11th, 2012, 16:58
i agree with everyone here too, go get a pair of 3:55 axles from an auto Xj, try to grab a pair from a later model with the 29 spline 8.25 in the rear. right now i have a 97 xj 4.0 5spd and had 3:07's with 235/75's, it had less balls than my old renix '89 4.0 5sp 3:07 with 30x9.50's no joke, renix definately had more torque . i put a '99 manifold and grabbed a pair of 3:55 axles with a 29 spline 8.25 for 200 bucks and life changed for the 97 xj lol, i know this is flame capable but i dont drive my xj fast by any means but if it has to get out of its own way no joke it'll actually shimmy a lil bit on a hard 2nd gear shift lmao. good luck man and have fun.

962door
February 11th, 2012, 17:16
I'm driving a 98 with the ax15 and some 30x9.5 bfg at's. Every now and then on long inclines I downshift but its fine driving around town and for freeway use. I'm planning lift and install 33x10.5's in the next few months then I will be regearing

Mike Mike
February 11th, 2012, 19:17
I ran 30/ 9.50s with 3.07 gears and they sucked , except in town. Not going to run anything bigger so I swapped in 3.55s and there awesome

volaredon
February 12th, 2012, 11:57
I have a 97 WRANGLER (along with my 97 XJ). this Wrangler is a 4.0 3.07 geared with an AX 15. When I got it the thing had the worst tires ever made on it; Wrangler RT/S' that were 215/75R15 (OEM original tires) I could not take off on even damp pavement w/o spinning had to use 4WD in the rain! (this being on pavement)
I went to Michelin LTX A/T 235/75R15s. man what a difference. on road or trail!
It has gotten better as the miles accumulated, power wise but 5th has always been a D-O-G below 65-70.
I put those Michelins on my 1st XJ and put some new 31-10.50s on the Wrangler. It went from doggy in 5th, to 5th being totally useless. I have another set of 235/75R15 Michelins back on there (it isn't lifted, stock height) and 5th is again at least somewhat useful on the highway.
While I hear "20 + MPG" stories all the time i'm stuck at 16-17. except when I drove from Chicago to Vegas and back; I never got so many miles per tank, before or since, than I did on that trip. I bought this Jeep@ 19K and now has 125K.
totally dead stock.
I do have a set of 3.73s for the rear but gotta wait til I get the funds to get the matching gears for the front to install them (along with new carriers since the "break" is 3.55)