I have a 2000 Blazer 4wd. I've been reading a lot on how having different size tires on the front and back can cause damage to the 4wd transmission. My father in law was nice enough to give me a new pair of tires for the front that he took off his astro van. The problem is the rear tires are p235 and the new front ones are p215, so 20mm difference. Is this going to be a problem? Do I need to remedy this immediately? Thanks in advance.

 

It wont be any problem to the transmission or any parts because the difference between the tires are just different widths. If there was a difference with tire height then yeah.

 

Front tires are p215/75r15
Rear tires are p235/75r15

Please correct me if I'm wrong...
235×0.75=176.25
215×0.75=161.25
For a difference of 15 mm
So the sidewalls of the p215 are 15mm shorter making the tire 30mm shorter than the p235. That's almost 1.2 inches difference in height, unless I'm missing something. Do I need to not drive it until I can match the tires or just not use 4wd?

 

So long as you stay in 2wd, nothing bad should happen.

If driven in 4wd (and/or Auto-4wd if 4-button), it will bind and if pushed too far, damage can occur.

 

Thank you.
Is there enough tolerance that if I were stuck, could I use 4wd momentarily to break free, or should I just not mess with it at all until I can buy new tires?

 

If you are in a low traction situation (snow, mud, sand, etc.), then you should be able to use 4wd. I would only use it to get yourself moving. You do not want to have it engaged on a high traction surface. That is when bad things can happen.

 

Thank you. I appreciate the info.

 

235/75/15 tires rotate at 689.39 revolutions per mile.
215/75/15 tires rotate at 728.17 revolutions per mile.

Imagine trying to get two gears to mesh when they are rotating at different speeds, it ain't pretty. As Kyle mentioned, on a high traction surface, it will do damage. In an absolute emergency situation, for a very short distance, at a very low speed, it might be OK. DO NOT shift the transfer case while the vehicle is moving. You'll have the same results as shifting a manual transmission into reverse while you're going forward.

 

Now I'm getting confused, so a wider tire will rotate less than a skinnier when they are both the same rim size and diameter!?

 

It depends on the tread width, and the aspect ratio. Tires 101: The first set of numbers is the width of the tread, in millimeters, from shoulder to shoulder. The second set of numbers is the aspect ratio. Both of the tires in question are "75". Which means the height of the sidewall is 75% of the width of the tread. The third set of numbers is the wheel diameter. As tread width changes, so does the height of the sidewall, and the circumference of the tire, which is what the OP is asking about. Sometimes there are other numbers after the size, such as "103T". The "103" tells how stiff the sidewall is. A "108" sidewall has a higher load carrying capacity than a "103", so it will give a stiffer ride. It will also provide a more stable feel in turns because the sidewalls aren't squashing down from the body roll. The letter refers to the sustained speed that the tire can safely operate.