Q: I have a 2000 Blazer that came equipped with Michelin 235/70R15 tires. After 99,000 miles, it's time to replace them, but Michelin now only produces 235/75R15s. Can the computer be reprogrammed to correct the speedometer being slow with the increased diameter of the 75-series tire?

A: I understand your loyalty to the OEM brand, and I agree regarding the quality of Michelin tires, but companies such as Cooper, BFGoodrich, and Yokohama manufacture 235/70R15s. The 235/70R15 tires were a choice on the ZR2 Blazer, and chances are the limited volume of sales promoted Michelin to cease production. The tire height (diameter) of the 235/70R15 tire size is about 28 inches versus the 235/75R15 at about 29. One inch is a significant change and will alter speedometer accuracy, which in turn affects the powertrain control system in general. There are several programmers out there, including Hypertech's Max Energy, which enables several adjustable features, including tire sizes from 24 to 34 inches in 1/4-inch increments. This fits the bill for your 1-inch increase in height. So, the choice is buying more expensive quality tires plus the cost of the programmer, or stick with the OEM tire size. That's your call.


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