Questions and Answers

Blazer 4x4 In A Bind Q. Dear Vince, I have a 1991 Chevrolet Blazer 4x4 with only 79,000 miles on it. I took it in for tires. The dealer said all I needed were two new tires. My normal tire size is P235/75R15 but he was out of stock so he mounted two P255/70R15 tires. I was always fighting the car but attributed that to the two new tires.

Winter came and I put the Blazer into 4 wheel drive. There may have been a total of 100 miles put on the vehicle when I noticed the truck took a long period of time coming out of 4-wheel drive and when it did it kicked as if I had hit a pot hole. Then I noticed an awful burning smell. I took the vehicle into a drive shaft specialist who told me my front differential was burned out and possible the transfer case. Although the transfer case was not affected, the front differential was definitely burned to a crisp.

My question is, did the different sized tires cause this problem?

Thank you for your help,
Loretta

A. I would say with almost absolute certainty that the tires were the cause of the problem. Let me see if I can explain why without getting too lengthy.

In a normal 2WD vehicle the front and rear wheels turn independently of each other. So it doesn't matter if the front and rear tires were a different size. But with a 4WD vehicle since the front and rear wheels operate together, size does become an issue. Okay, now comes the tricky explanation. When you have two tires with a different circumference, the tire with the larger circumference will cover more ground per rotation than one of a smaller circumference.

In a 4WD vehicle since all four wheels are directly tied together, this becomes a problem in that the larger circumference tires will travel further than the smaller tires. In essence your front tires may travel 10 miles and your rear tires may have traveled 12 miles in the same period of time. This difference gets compounded the longer you drive. After a while, something has to give. Sometimes it will "kick" or the bind will get so bad that parts start burning out or breaking.

Whenever you put new tires on a 4x4 the circumference of all the tires must be checked and be within a half an inch of each other.

I hope I explained this well enough to be understood.

Additional Information provided courtesy of ALLDATA

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