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Old 08-03-2013, 03:40 PM   #9 (permalink)
gone-ot
...beats walking...
 
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I just take my car to the local speedometer shop and have them test it on their chassis dynamometer at exactly 60 mph and compare their value against the simultaneously read ScanGauge II value, which then gives me a "scaling coefficient" for the ratio between "actual" and what the ECM "thinks" the wheel is turning (which includes tire diameter).
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