How to work out wheel circumference for bike computer?
Thursday, December 2nd, 2010 at
8:12 am
Question by John: How to work out wheel circumference for bike computer?
I’m fitting a bike computer and on the chart of popular bike wheel circumferences, it doesn’t show 26 x 1.6 which is my tire size.
Best answer:
Answer by andy_goodnight
Normally they have set sizes. I just used the closest.
Know better? Leave your own answer in the comments!
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Try this link…
http://www.sheldonbrown.com/cyclecomputer-calibration.html
You could work it out with maths (circumference = pi x diameter) or you can measure it by wheeling your bike for one revolution of the wheel and then measuring the distance it travelled.
put your bike on a flat surface. Mark the spot on the ground and the tire where the tire meets the ground. Move the bike until the tire goes 1 revolution (tire will be marked so you’ll know when to stop). Mark the ground again when the revolution is complete. measure from the first mark on the ground ot the second.
That is the most accurate way of doing it. Better than even following the tire size specifications on the chart in the instructions.
Good luck.
All bicycle tire from differrent manufacturers is not exactly same. Set up wheel circumference for 26x 1.6 tire is 201 mm or 202 mm .
It will change with the manufacturer of the tire but 1985 mm will get you very close. You can do a roll out test. Put the valve stem at the bottom and make a mark, roll the wheel until the valve stem is at the bottom again and make another mark. For accuracy have your weight on the bike when you do it and use 3 rotations and divide by 3. Something as simple as tire pressure and your weight will make a difference but it will be only a few mm.
Like a bunch of answers suggest, roll the bike 1 wheel revolution and measure the distance in cm. I’ll use the valve stem as my reference. You are going to be somewhere in the range of around 2015 cm.