Originally Posted by
Retro Grouch
If you think that "good enough" is good enough, just program in whatever tire circumference number the computer set up instructions suggest. You might be off by a couple percentage points but that's - well - good enough. If, after finishing a ride my computer says 49.88 miles, I don't ride a lap of the parking lot because I think that "good enough" is good enough and nobody else cares anyway.
If you're the kind of person who has to have all his clocks indicate exactly the same time, you need to roll out your tire. I'd roll it out for 3 or 4 revolutions and divide to minimize your measurement error. You can minimize, but you can't completely eliminate measurement error. In the end, all you've really accomplished is to redefine "good enough".
You just described me to a "T".
I have indeed ridden a circle around the parking lot to get my cyclometer to read 100.1 miles when the century ended with it showing 99.8 miles! And yes, I hack my watches against the NIST atomic clock.
As to cyclomneter calibrations, i have indeed done the roll-out procedure and the Cat-Eye calibration table seems very close to what I came up with. Also, various makes and models of "700x23" tires differ slightly in their true dimensions so you would have to repeat the roll-out with every tire change. I don't. i do set the calibration number slightly under the theoretical value (2090 vs 2098) and assume my actual distance is at least as far as the reading.