Originally Posted by HillRider
"Rollout" measured with the correct tire pressure and your weight on the bike is, theoretically, the most accurate way to determine the true wheel circumference but it has to be done properly or it's no better than the calculated value. You will be right within a fraction of 1% if you use the calculated value.
The discrepancy is more if the sensor works off of the rear wheel, less if off of the front wheel. I tend to forget that because I've always run rear wheel pickup computers.
