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biggest allowable tire size with stock axles?

you can run 35's on a d30 if you throw $ at it, you can also get some waggy 44's and get rid of unit hubs ect and put 35's on them with confidence. It comes down to how you wheel, where you wheel/how often
 
Ive had a IRO 5.5" longarm for 3 years havent had any problems with the long arms at all... now brake lines and leafs springs i have... Early on they used out of house lines well those blew apart. And they shipped one leaf spring with the center hole drilled in the wrong spot.
 
if you want a good lift save your money and go with a rockkrawler or clayton I would say RE but no longer know of their quality.
 
I’ve broken 8.25 shafts. Broken D30 shafts. Broken chromo 44 shafts. Broken 300M u joint. All on 35s. The only thing that lead a trouble free life was my 35 spline 9” (chromo shafts).

Really come down to your usage. But 37s are beyond what most would deem “acceptable” for a D30.
 
U really think I have to upgrade brakes for 35's? I really wanna get the 8 inch lift and put in 35's cuz 33's with 8" is obv too small. And by swapping, what does that entitle?

You sure you want to go 8"? I just installed the IRO 4" short arm lift and minimally trimmed my fenders and have room to spare for 33x12.5 tires.
 
You guys know this thread is 10 years old, right?

Hehe..I didn't notice. To be fair, if you started a new thread someone would accuse you of not searching. BTW, this is my IRO 4" short arm lift with 33x12.5 tires. Rims are Quadratec 15" with 4" backspacing. I only minimally trimmed my fenders and feel like I could easily fit 35" tires.

I just had the rear diff re-geared with 4.56 gears and I am wondering if I should have went with 4.11 gears. At ~60mph the RPM is 2200 which isn't too good considering I travel the freeways a lot. On the other hand, I might like the lower gears when it comes time to tow something. I am considering moving up to 35" tires when these wear out. Thoughts?

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In my experience with the more aggressive types of rock crawling a built d30 and 8.25 are reliable with a 33 inch tire. Anything larger than that and you are on borrowed time. Sure you can mud with bigger tires but if you are rock crawling with lockers, 33s are the limit imo.
 
'I just had the rear diff re-geared with 4.56 gears and I am wondering if I should have went with 4.11 gears. At ~60mph the RPM is 2200 which isn't too good considering I travel the freeways a lot. On the other hand, I might like the lower gears when it comes time to tow something. I am considering moving up to 35" tires when these wear out. Thoughts?'

My thoughts, I have two XJs. One is on 32.5 and 4.10's, it was on 31's and 4.10s. With 31's it was good. I forget what it RPMed at. With the 32's its a bit doggish at times. It might be one of the speed sensors on the trans. Still, it was fine on 31's. I would say, I'm at 2,200 at 70 mph. I think 4.30's would be right for it. I use it mainly as DD and highways.
My 'new' one is on 31's and 3.73's. It does good. I did take a trip a week or so back, through WV and PA, then Ohio and back to IN. Except WV, I did not have not real issues. In WV, I had to down shift to 3rd many times. I was at 1,800 at 55 mph, 2000 at 65 mph and 2200 at 70-75 mph. I was between 17.4 and 18.3 mpg. Also, a leak at the exhaust manifold and old O2 sensors. See what it does with a compact header on it.
So, if you like the MPG you are getting, I'd leave it alone or not worry about it. Also, I'd think if you go with 35's, you'd be good. Also, did you change out the Speedometer gear?
 
My thoughts, I have two XJs. One is on 32.5 and 4.10's, it was on 31's and 4.10s. With 31's it was good. I forget what it RPMed at. With the 32's its a bit doggish at times. It might be one of the speed sensors on the trans. Still, it was fine on 31's. I would say, I'm at 2,200 at 70 mph. I think 4.30's would be right for it. I use it mainly as DD and highways.
My 'new' one is on 31's and 3.73's. It does good. I did take a trip a week or so back, through WV and PA, then Ohio and back to IN. Except WV, I did not have not real issues. In WV, I had to down shift to 3rd many times. I was at 1,800 at 55 mph, 2000 at 65 mph and 2200 at 70-75 mph. I was between 17.4 and 18.3 mpg. Also, a leak at the exhaust manifold and old O2 sensors. See what it does with a compact header on it.
So, if you like the MPG you are getting, I'd leave it alone or not worry about it. Also, I'd think if you go with 35's, you'd be good. Also, did you change out the Speedometer gear?

Thanks for the info. I haven't checked my mileage yet, but if I go too much over 60 mph I can watch the fuel gauge move. And yes, I did change my speedo gear. I am seriously leaning towards just being patient and going with 35's next time. I am on the TX coast, so my offroading is almost exclusively sand and occasionally mud, which should be easier on the D30?

BTW, I did my 500 mile gear oil change on the new gears last night...wow...it looked like a thick gray milk shake.
 
Thanks for the info. I haven't checked my mileage yet, but if I go too much over 60 mph I can watch the fuel gauge move. And yes, I did change my speedo gear. I am seriously leaning towards just being patient and going with 35's next time. I am on the TX coast, so my offroading is almost exclusively sand and occasionally mud, which should be easier on the D30?

BTW, I did my 500 mile gear oil change on the new gears last night...wow...it looked like a thick gray milk shake.

don't think that's normal. you get water in the diff somehow?
 
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