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Tires not matching ('00 Mounty)

Mesozoic

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My recently acquired '00 Mounty has Goodyear 235-75-15 tires all around, but the rears are Wrangler ATs and my fronts are SR-As. Two very distinctly different tread patterns. My friend, who is a mechanic, tells me that I should look into replacing all of my tires with new ones or at least match the rears (they're better tires, apparently). Does this sound like a good idea?
 


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koda2000

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For AWD this is absolutely correct. Not only is the same size tire with same amount of remaining tread important, but different brand tires (even the same size) can vary in diameter/height slightly and this is bad for the AWD viscous coupling. Ford recommended that the tires should not vary by more than something like 1/32 of an inch. You should also rotate your tires often to keep the tread wear the same.

The viscous coupling in the center differential/t-case heats up when slippage is sensed. It interprets different tire size as slippage. Running the coupling hot all the time will ruin it.
 




Mesozoic

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I was looking at some Kumho AT51s in 31x10.5x15. Does that sound like a reasonable replacement and upgrade?
 




XLTrunner

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It's not just AWD trucks that are affected by uneven tire diameters...4WD are also affected for the same reason in that the transfer case will interpret different diameters as wheel slippage and cause undue wear on it. I believe the difference should not be more than 3/32" among tires.
 




Mesozoic

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I think that the Mounty has a 15x6 wheel, so I think I might be in the market for a wheel upgrade as well. What is the correct offset to run for 15s and what about 16" wheels? I'm thinking that a 15x8 is the minimum width required to run a 31x10.5 tire.
 




koda2000

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It's not just AWD trucks that are affected by uneven tire diameters...4WD are also affected for the same reason in that the transfer case will interpret different diameters as wheel slippage and cause undue wear on it. I believe the difference should not be more than 3/32" among tires.

OP's truck is an AWD, so that's what my response was addressing. You're probably right about the 3/32" difference. It's been a while since I read the owner's manual and 1/32 is a tiny, tiny amount of difference.
 




Mesozoic

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Well, it may have been an impulse purchase, but I'm planning to travel into snow country in the Mountaineer for Thanksgiving. I bought some tires and wheels off of tirerack.com; AR 15x8s with Kumho AT51 in 30x9.5x15. I hope it all fits.
 




colintrax

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A little late, but I don't think you'll be too happy with that wheel tire combo. Stock wheels are 7" wide not 6"
An 8" wheel is going to sit pretty flush with the sides of a 9.5" tire
 




Mesozoic

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There's nothing particularly bad about that is there? Tire calls for a 6.5 to 8.5" rim. If anything, I'd be worried about the offset... it's going to stick out almost 2" further from where it is now, but that might just fill out the wheelwell nicely.
 




CDW6212R

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There's nothing particularly bad about that is there? Tire calls for a 6.5 to 8.5" rim. If anything, I'd be worried about the offset... it's going to stick out almost 2" further from where it is now, but that might just fill out the wheelwell nicely.

An 8" wide rim should be around the 20mm offset range. Anything much more than that will be getting too close to the BJ's. I had 30mm 8" rims with one set of tires, and it needed 6.35mm spacers that I bought later. So go from there, 30mm is pushing the limits inboard, 25mm leaves a safer clearance.
 




Mesozoic

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I believe these wheels have a -18mm offset, so should move the rim outwards towards the wheel openings. I've heard of several other folks use this wheel on a 2nd gen, so I figured that it would be a safe bet.

IMG_0237.jpg
 




429CJ-3X2

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My '02 Sport Trac had stock size 235-70-16s on AR 8" rims when I bought it. I would have gone with 7" rims if I had been buying. I can't ever remember the offset and got a couple of figures last time I looked it up. I think it's -12mm with 3.75 backspace. Whatever it is, clearance is close on the inside, but it works fine.
 




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The offset can be + or -, almost everything you find will be positive, no character shown. I hope your wheels are positive offsets, because negative would be outboard by about 1.5 two inches(+20mm minus -18mm = 38mm outboard more(1.5")).

The wheels pictured look good, about right.
 




Mesozoic

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Got the wheels installed last night and it is a huge facelift for the truck. The front tires do stick out a bit, but they look good doing so. The rear tires stick out minimally, if not flush with the rear quarters. The 30x9.5x15 sizing was definitely correct as it works well, no rubbing.
 




koda2000

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Got the wheels installed last night and it is a huge facelift for the truck. The front tires do stick out a bit, but they look good doing so. The rear tires stick out minimally, if not flush with the rear quarters. The 30x9.5x15 sizing was definitely correct as it works well, no rubbing.

How about a photo?
 




Mesozoic

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Not the best snaps, but...


 




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Does the Bronco run? How much do you want for it?
 




Mesozoic

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Does the Bronco run? How much do you want for it?

Yep, my '79 is in full effect. It's my dedicated offroad rig, although it's got full interior (minus carpet, all Herculiner), air conditioning + heat, fuel injection, lockers, lift, etc. We needed the Mountaineer for milder family trips since the Bronco is such a beast!
 




koda2000

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The new wheels look good.
 


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intelisevil

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Got the wheels installed last night and it is a huge facelift for the truck. The front tires do stick out a bit, but they look good doing so. The rear tires stick out minimally, if not flush with the rear quarters. The 30x9.5x15 sizing was definitely correct as it works well, no rubbing.

Those tires are almost the same diameter/circumference as the factory option 255/70-16 tires. The factory options are about 1/2" wider.

https://www.tacomaworld.com/tirecalc?tires=255-70r16-30-9.5r15

I had some odd shifting issues when I went from 235/75-15 to 255/70-16 tires on my '99 Mounty AWD. After I recalibrated for the larger tire size, it disappeared. I haven't read anyone else post about this problem so maybe it was just me?
 




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