Quote:
Originally Posted by WVZR-1
George and I have both used the "advertised" diameter for a 315 tire but when I did mine a few years ago I did it with "rolling tire radius" from my car which directly affects the speedometer and it would be interesting to see George's Exel done with that. It's not a major discrepancy but that's how the factory calibration is theoretically done. The number 25.4 seems familiar and that would be 12.7 X 2!
I've always felt the advertised diameter should do but it does get debated.
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You're absolutely correct ... using the "advertised" diameter is only "theoretical" but probably doesn't have a major discrepancy ... at least not for "comparison" purposes. And here's yet another curiosity ... the default on the Excel file is set for the Z's standard rear tire, but if you change to the front tire size, the diameter changes slightly. And what about differences in tires by different manufacturers even though the tires are stamped the same size? Yes, the debate goes on.
George