So i got some 265/75/16's out back and 265/70/16's in the front. my boss was trying to tell me if i put the truck in 4WD it will blow the transfer case cuz of the different size tires. i dont think this is true, anyone know anything that could help me? cuz i wanna go take it muddin soon.

 

The only difference I see in your tire size is the width measurement, i.e. 75 vs. 70. If the tire diameter is different it can damage your x-fer case due to the different rates at which the tires will rotate.

 

Well actually, the 265/70/16 is a 30.60" diameter tire, and the 265/75/16 is a 31.64 tire. That is about 1" diameter difference, way more then I would be comfortable with in 4 wheel drive. I think I agree with your boss on this. However, it could also depend on how worn they are. You should measure them yourself to see exactly how different they are. Mark the tire and the ground. Then drive until the mark on the tire is back to the ground after one rotation. Measure the distance between your ground marks. Do this on the other size tire, and compare the difference. If it is significant, i'd be leary of putting it into 4 wheel drive.

V10Jim, the 70/75 number is the aspect ratio, which is a combination of the tire width and the sidewall height. So it does impact overall diameter, not just width.

 

your boss is correct. don't drive in 4wd with different size tires.

 

yeah, your boss is right, as everyone says, although, if it is in mud because the tire restriction will be almost nothing as long as its not sticky clay mud it really shouldnt hurt it, but the risk is that you could be spinning those tires hard and then hit a hard spot and blow out your transfer case real bad. I actually just learned about all this recently, so I also had a question to add to this, because I have the stock size spare, and I have 285/75/16's if I blew out a rear tire, would it be safe to put the smaller tire on the front axel and move the front tire back to the rear blown out tire so that I had both 285's in the rear? or would that just blow out my transfer case even out of 4wd??

 

assuming you have regular open or lsd rear differential (as opposed to a spool), different size tires on the left rear and right rear will not hurt anything. the differential is built to allow different rotations at each side. same with the front differential, it can handle different sizes on left and right. the only thing the truck can't handle is different tires or gears on front vs rear, because there is no center differential. our trucks are part time 4wd, not full time 4wd, so the t-case delivers equal rotations to front and rear. any slippage must occur at the tires.

so, if you had to put on a spare of smaller size, the truck might drive better with the odd size on the rear, rather than the front. either way it won't hurt anything, but as instructed in your owners manual - only use 4wd on slippery surfaces (mud, snow, dirt, wet pavement) as opposed to dry pavement.