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Our '02 has the 265/70-16 aluminum wheels with worn out Firestone Wilderness LE tires. I'm thinking that since 17" were an option that would be a nice appearance upgrade and keep the 16" for dedicated snow tires.

However, I don't want to introduce speedometer and odometer error by going to the optional 265/70-17 wheel/tire combos.

How do the factory guys do this? is there some speedo electronic setting that is changed via a programmer? Or is it within the speedo error margin anyway?

According to the miata.net tire size calculator, the optional tire size would cause the speedo reading to be 3.3% too slow, or at indicated speed of 60 mph the actual speed is 62 mph.

Your thoughts?
 

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Simple reprogram of the PCM. (Powertrain Control Module) Simple but not inexpensive. My buddy raised his 05 Silverado and went bigger on the tires. He shelled out $500 for a Hypertech to recal the PCM for the change. Silly me, I thought I could borrow it to fix the speedo on my 06, but you can only use it on one vehicle at a time. Since it is a work truck, I just put up with the 3mph difference on the speedo.
 

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Go and look for 265/65/17 . They're almost the same in diameter as the stock tire, your tach doesn't have to be adjusted that way. 60 mls on the tach will be 59.9 so hardly noticable
 
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