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Discussion Starter #1
I searched but found nothing to help me with this.

My question is about running two different size tires on the same differential. I am running 32” BFG mud tires on the truck, but the spare is the stock 31” size, till I wear out the BFG’s and make one a spare.

I know about open differentials and how they allow for the wheels to spin at different speeds, for reason of cornering, wheel cheat…. And I am aware of why we use lockers and the affect they have on the differential.

Still, the thought of running down the highway @ 65+ with two different size tires gives me the willies. My thought is that if I do need to run the smaller spare I would simply mount it up front and unlock the hubs and this would hopefully get me to the tire shop.

Can anybody tell me if it is ok to mount two different size tires on the rear and drive without concern for the health of the differential?
 

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Bent Wheel said:
I searched but found nothing to help me with this.

My question is about running two different size tires on the same differential. I am running 32” BFG mud tires on the truck, but the spare is the stock 31” size, till I wear out the BFG’s and make one a spare.

I know about open differentials and how they allow for the wheels to spin at different speeds, for reason of cornering, wheel cheat…. And I am aware of why we use lockers and the affect they have on the differential.

Still, the thought of running down the highway @ 65+ with two different size tires gives me the willies. My thought is that if I do need to run the smaller spare I would simply mount it up front and unlock the hubs and this would hopefully get me to the tire shop.

Can anybody tell me if it is ok to mount two different size tires on the rear and drive without concern for the health of the differential?
I wouldn't do it all the time and if you could I would get a cheap used spare from someone on here, but to get you home from the trail, it should be fine.
 

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Discussion Starter #3
TACO 4X4 said:
I wouldn't do it all the time and if you could I would get a cheap used spare from someone on here, but to get you home from the trail, it should be fine.
Thanks Camo Tow,

I may just poke around for a used 32”.
 

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I agree that it's OK for a SHORT time, but I have found it's better on the rear than on the front. The steering acts very strange with two different size tires on the front (admittedly, when I did it one was a bias-ply and the other radial, so that may have had a lot to do with it)
 

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Bent Wheel said:
Thanks Camo Tow,

I may just poke around for a used 32”.
Or you can go to Discount tire or something and get a new 32 for prob $100 or so.
 

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Discussion Starter #6 (Edited)
RedRunnertc said:
I agree that it's OK for a SHORT time, but I have found it's better on the rear than on the front. The steering acts very strange with two different size tires on the front (admittedly, when I did it one was a bias-ply and the other radial, so that may have had a lot to do with it)
Eeewww,

I did not think of the steering factor…

Say, lots of cars come with a so called “space saver spare” I guess that should answer my question about running different size tires. Although I have never read the instructions for a “space saver spare” maybe the instructions say to mount the space saver on a non drive axle?

Still as a non expert in the differential department I will look for a 32” spare.
 

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I have a good tread stock spare (265/75r16) with wheel (3/8-1/2" tread), and 2 32" BFG AT's just tires with about a 1/4" tread up here near Sacramento for $20 apiece if you are interested.
 

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I bought a set of 32' BFG's and when they installed them one had a problem, so they went and got another one and put it on no problem. After driving for quite a while By brother wanted to get a set of tires so I went out to read the size to him and the one I read was 31x10.5. What the hell I thought? Looked at the others and they were all 32x11.5. I never noticed a steering difference, (odd sized on the front.) Only noticed it was hard to get out of 4WD. So It won't make a steering difference, but will work the rear diff a bit more. Over all, it won't make much of a difference. For a spare, I wouldn't worry about it.
 

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Discussion Starter #9
Rattlecanpaint said:
I bought a set of 32' BFG's and when they installed them one had a problem, so they went and got another one and put it on no problem. After driving for quite a while By brother wanted to get a set of tires so I went out to read the size to him and the one I read was 31x10.5. What the hell I thought? Looked at the others and they were all 32x11.5. I never noticed a steering difference, (odd sized on the front.) Only noticed it was hard to get out of 4WD. So It won't make a steering difference, but will work the rear diff a bit more. Over all, it won't make much of a difference. For a spare, I wouldn't worry about it.
Rattlecanpaint,

Thanks for sharing your experience; it sums it all up for me.

In ten years I have never had to use the spare. I think I’ll keep the stock 31” as a spare till I get new 32”s.
 
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