Re: Setting tire size in computer
Originally Posted by Insight Driver
Do the rollout test as suggested, best done by actually sitting on the bike while someone helps you so that you get the true radius. The number you get will let you see if you want to round up or down to the nearest increment you enter into the computer. You see that you can't nail it exactly, your computer is granular, only allowing whole integer input. Such is life. You don't need any more accurate, do you?
Let's see. If you are able to adjust to the nearest mm, then at most you should be off by 0.5 mm. That is a 0.023% error. If the average is 2130 mm, and you are off by 0.5 mm, then over the course of a 100 mile ride, your error would be 124 feet. I think I could live with that.
Even if you could only adjust to the nearest cm, and you are off by 0.5 cm, that is a 0.23% error rate. The error in 100 miles would be less than 1/4 mile.
To look at it another way, at 20 mph, the error in the displayed speed would be 0.005 mph (for those computers that calibrate to the mm) or 0.05 mph (for those that calibrate to the cm).
I doubt that the tape measure you use to measure the roll out distance is any more accurate than that.