Does anyone know the L(mm) for a 20" 1.10 tire for entering into a cyclocomputer? Thanks.
L(mm) for Setting Up Cyclocomputer?
As always, Sheldon may have your answer.
That being said, the most accurate way is to measure it yourself. Here are two ways:
1 - Mark or find a line/spot/mark on the ground. Put your valve stem exactly down and on top of the line/spot/mark. Roll your bike until the valve stem is again exactly down. Mark the spot and measure between the two spots. This equals the circumference of your wheel for entry into the cycling computer.
2- Measure from the center of your hub down. That is the radius. Circumference = (2)(pi)(r) where pi ~ 3.14159 and r = radius.
note: you may need to convert the unit of measure to the unit the cycle computer requires (ie, mm to inches, etc.). Here is an online conversion calculator to help you.
Measure it with a GPS or google tracks and then calibrate your computer to that, changing the wheelsize as necessary until the speed on the cyclecomputer matches the speed on the GPS.
Even better if you are sitting on the bike and your tires are inflated to their normal pressure (so the radius, and therefore the rolling circumference, is as accurate as possible), and then you roll the bike 10 revolutions of the wheel. Divide the nistance between the marks by 10 to find the wheel circumference. Any error in measurement will be reduced by a factor of 10.