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diff -vs- tire size

wrecklaw71

NAXJA Forum User
Location
Indiana
I have a 2001 ckerokee sport 4.0 , d30 front 8.25 rear, planning a 3.5 lift and 31's seems like this combo should be ok for the stock diffs/axles, but what do you guys think. It's a daily driver and i've also planned some type of locker or posi any ideas on what might be best for this scenario? also the stock gears are 3.55 would a 3.73 be enough to compensate for the tire size?Thanx
 
3.73 isn't a big enough change to be worth doing. If you can pick up a set of complete 4.10 axles go for that, but even then if you have to pay for installation it's going to be expensive without noticeable gains.

The axles will be fine with that combo. No current recommendations on locker/limited slip.
 
3.5" lift and 31s will be fine for stock gears/axles. In reality you would need 3.90s with 31s to equal what 225s were with 3.55s. I run 3.55s with 31s for the time being and it is fine.
 
Wrecklaw - yes, that's what I recommend. jeepguy's calculation of 3.90s isn't available for your axles, which is why I'd recommend the preloaded 4.10 axles if you can find them. Gear and setup costs are too high to get any kind of benefit off the otherwise small change.
 
Will be OK but some less giddy-up on the road vs what your Jeep has now.

Changing gear ratios (and adding traction diff's) is expensive... 4.10 will be slightly lower ratio than stock, and that will help offset the increased weight/drag of the 31" and the 3.5". 3.73 might look good on the calculator, but would be a pain in the wallet when they come up short.

<edit> Exactly what they said above... Look for a 4.10 hi-pinion axle out of a 92-98? 4-cyl XJ, freshen it up and install it (with your 01 brakes/hubs) when you do the rear... Did they make a factory 4.10 8.25??? If so search one of those up too. I decided on 4.56 for my 31" rig... but I don't do a lot of freeway travel.
 
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has anyone used the Powertrax /Lockright type of diffs ? do they hold up to trail use ,also itseems that type of diff could be hard on axles versus a standard locker. whatcha think?
 
wrecklaw71 said:
also itseems that type of diff could be hard on axles versus a standard locker. whatcha think?
Technically, the type of locker is harder on the axle since the diff is part of the axle assembly. What you say is fairly true though, which is why open-diffed D35s live longer lives than ones with a Detroit or spool. That's not really a concern with the 29-spline C8.25 or your D30 though.
 
i ran the same combo for a long time and it was just fine. also had a lock right up front(hp though). 31's w/3.55s are fine, definetly not ideal but it is fine. i also ran the same but with 4.56s for a while. if your not going to be doing much of any highway travel then i would suggest going to the 4.56s. its fun and you'll never lack power.
 
Yucca-Man said:
Wrecklaw - yes, that's what I recommend. jeepguy's calculation of 3.90s isn't available for your axles, which is why I'd recommend the preloaded 4.10 axles if you can find them. Gear and setup costs are too high to get any kind of benefit off the otherwise small change.

Correct, I was just letting him know that 3.90s would get him back to stock. So 4.10s would be the way to go....stock plus a little more.
 
jeepguy97 said:
3.5" lift and 31s will be fine for stock gears/axles. In reality you would need 3.90s with 31s to equal what 225s were with 3.55s. I run 3.55s with 31s for the time being and it is fine.
hell yeah, im runnin 31s with the stock 3.07 and it sucks. need new gears but was quoted $1800 for gears carriers and instal. and im in high school. no chance of have $1800 dollars...
 
I'm running stock 3.55 gears with 32's and seem to have plenty of launch power (read "can smoke them (one back tire) on a hard launch"). Gas milage seems to be suffering a bit (not a surprise) but all the loss power stories I've been hearing haven't seemed to come true. Any thoughts?
 
Dylan90xj said:
I'm running stock 3.55 gears with 32's and seem to have plenty of launch power (read "can smoke them (one back tire) on a hard launch"). Gas milage seems to be suffering a bit (not a surprise) but all the loss power stories I've been hearing haven't seemed to come true. Any thoughts?
Yeah...I think that when you regear to 4.56 you'll be amazed at how much you've given up thinking that 3.55s and 32s are a good match. Been there, done that along with a few dozens of other board members.
 
wrecklaw71 said:
I have a 2001 ckerokee sport 4.0 , d30 front 8.25 rear, planning a 3.5 lift and 31's seems like this combo should be ok for the stock diffs/axles, but what do you guys think. It's a daily driver and i've also planned some type of locker or posi any ideas on what might be best for this scenario? also the stock gears are 3.55 would a 3.73 be enough to compensate for the tire size?Thanx
I'm running 31s and 3.73 gears in an MJ. The overall final drive ratio (RPMs per MPH) is exactly the same as stock tires and 3.55 gears. It's driveable, but not what I would consider ideal. I originally bought the gears to run with 30" tires -- the 31s sort of happened.

If you want to run 31s, go with 4.10 gears.
 
I originally put 31's on my AX-5. Bad idea. Got a D44 with 3.55 gears and a new front D30 with the same and now it runs just like it did when I had 235 75 r 15's.

The bigger you get, the lower the gears.
 
i have been running 31" muds and now 32 inch swampers with a 30 and yes a 35. no slip in the rear for the last 4 years and a no-slip in the front for one year. never broke an axle yet. just last weekend i did put in a set of rear yukon axles (put a set up front last year). just don't be stupid and hold it to the floor all the time and your axles will live, if money is no object, go for the hammer down, and get 44's front and rear or the strength and brand of your choice.
 
If your going to keep your 8.25 long term then go straight to 4.56's, that is IF your going to spend the money on a gear swap. If you can find a hp 30 out of an earlier XJ 4cyl then perhaps the savings could be worth going to 4.10's that is kind of what I did but now I wish I would have gone straight to 4.56's since 31's just don't seem like enough sometimes...

Just my .02 cents.

Brian T.
 
Yucca-Man said:
Yeah...I think that when you regear to 4.56 you'll be amazed at how much you've given up thinking that 3.55s and 32s are a good match. Been there, done that along with a few dozens of other board members.

Well ya that's kinda my point, what am I giving up? If the issue with 3.55 gears is strength or grunt while rock crawling then it makes sense to spend the cash on re-gearing...but I really don't seem to notice a major difference in daily driving. The fact that I have plenty of get up and go at the lights (more than I can put to the road with open diffs) then I can't be pulling away any faster than I was with stock tires. Please don't get me wrong...there definately seems to be alot more guys out there with more experience with this than I have (so I'm not arguing) but I was totally expecting my XJ to pull slowly away from the stop lights when I went to 32's and that doesn't seems to be the case.
So while I was expecting a change I am "amazed" at how little it was and with this small of a change I would plan on spending $ on lockers or 44's not on re-gearing for a small (if any) gain in acceleration from a stop.
Thanks for the reply
 
I've got 32's and 3.55's, and while it is fine around town, once I get on the highway they just aren't enough. Cruising at 70 MPH my RPM's are a tad below 2250, which is too low. Any little rise in the road causes a downshift/upshift dance to be performed by the transmission. Not what I would call fuel efficient. I am going with 4.56 in my '99 D30/8.25 combo and I should be right back in the sweet spot.

Greg
 
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