Setting your bike odometer just right:
- Walmart.com: Bell Sports F-20 Bike Computer: Bikes, Scooters & Skates
- Bell F20 manual.pdf
- In case this is all you need, here are the wheel values for a Bell F20 (they are just the lengh of a wheel rotation in millimitres)Road Bike20" 159622 175924 191626 207327 2124Mountain Bike24" 188826 204527 215528 2237
The values on the chart will generally give a value accurate to within one or two percent, which is more than good enough for the vast majority of cyclists, and is much more accurate than most automobile odometers.
If you require more accuracy, you can do a "roll-out" test. Since the effective tire size is affected by tread thickness, tire pressure, and rider weight, the rolling circumference should be measured (in millimetres) by rolling the bike with the rider aboard for one wheel revolution.
You may use the valve stem as a reference, starting the roll with the valve right over a perpendicular line on the floor, and ending when the valve is back at its low point one revolution later.
Another approach is to put a small dot of paint on the tire and measure (in millimetres) the distance between the marks that the paint prints on the road.
With either approach, the rider must hold the handlebars absolutely straight while an assistant balances and pushes the bike. Otherwise, the wheel may not follow a straight path.Source.
This is another manual but it seems incomplete.
