Dumb ? maybe but I have bf goodrich all terrains 285/75/r17 on all 4 rims. my spare is still the stock size whatever it is (265/70r17?) If i get a flat tire and put the spare on will i injure diff? and if so what speed and how far can i go?

 

I don't know from personal experience.......

But I was told that you can put the spare on the front and you would be ok, even if it was a different size from the others. Hope so anyway, as im running a 285/70/17 spare right now........with 35'' tires on the ground.

Then again......when was the last time anybody had a flat? I have never had a flat with this truck.........thus far....in 97K miles. Im sure it happens but not nearly as often as with prior (smaller) vehicles.

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Find a used 285 tire to use for your spare. I shelled out the extra bucks for another 285 when i bought my tires just so I wouldn't have to worry. My biggest concern would be if I was towing and had a flat. I would not want 10,000lb behind a mismatched set of tires on the rear of my truck...

 

Don't know where you are located. If close to Houston then I might can help.

I have two BFG 285/R70/17 A/T KOs in the garage. They have about 40-50% tread left. I blew out one of my four, so I just bought a new set. Put one of the three on as spare and the other two are in the garage taking up space.

 

As long as you do not have a full non-selectable lockers you will be fine to use in in an emergency.

 

Had a blowout about 6 months ago driving to New Mexico. Put the factory size spare on the front (265/70R17) and everything workout out fine. Do not use 4X4 while you have the tire on.

 

X2 on Floyds advise.

 

You can run the mismatched size on the front since there is no limited slip in the front axle. If you try to run unmatched sizes on the rear with limited slip, you will tear up the limited slip since each side will be turning a different speed. You can drive short distance at slow speed, but I wouldn't go very far.

I switched to 285s shortly after getting my truck, but I didn't replace the spare with a 285. I blew a tire on the driver side rear on I-35 one night heading to Giddings. I know people must have thought I was crazy since there I was pulling the perfectly good front wheel off and replacing it with a spare. Meanwhile the back wheel is laying on the rim.

BTW, you just jinxed yourself Robert....you'll have a flat before you know it now.

 

I think that when you put the smaller tire on the front-your front driveshaft will actually turn slower.-but that would be based on not having the 4x4 engaged.

Just make sure that your smaller diameter tire doesn't go onto the rear axle...

 

Your spare is worth about $100 on eBay if it's still new. I put on a set of 285/75's on my '05 recently and sold my unused spare because of the size diff. I went from a 285/70to the 75's and thought and kept one of those for the spare.

If anyone has some old LT285/75R15 gathering dust speak up or about to replace some. I think there are some folks willing to help you keep your garage or landfill clear!

 

I'll bet you are right...

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So how much does it take to actually make a difference?

Lets say you have some mudders with 21/32" of tread. You buy 5 so you can have the same sized spare. If you don't include the spare in the rotation,you might get a flat 2 years from now when you have 50,000 miles on the tires.

If the spare has the original 21/32" but the tires on the truck only have 5-6/32" thats 1/2" difference in diameter.

Is that enough to cause problems?

 

FWIW, I've had good luck finding great used tires (>= 6/32nds tread depth) at the local Discount Tire Center(s).

 

Theoretically yes, probably not, but in that case you can let enough air out of the new spare to compensate for the difference pretty easy and still not have a problem driving on the rear for necessary period.

 

Find a good used tire the correct size, only for your piece of mind.