# Thread: Question on wheel size setting on bike computer

1. ## Question on wheel size setting on bike computer

When I set the wheel size setting on bike computer for the wheel size factor, should it be the diameter of the wheel only or wheel + tire?

Thanks!

2. Outer diameter of tire on wheel. Some people using chalk on the tire, roll it and measure the distance from chalk to chalk as it leaves the chalk imprint on the floor.

3. Originally Posted by danhasdrums
Outer diameter of tire on wheel. Some people using chalk on the tire, roll it and measure the distance from chalk to chalk as it leaves the chalk imprint on the floor.
Thanks! But you can actually just multiply the diameter by pi=3.14159265.

When I set the wheel size setting on bike computer for the wheel size factor, should it be the diameter of the wheel only or wheel + tire?

Thanks!
Most computers use the rolling circumference of the tire in mm or cm for the calibration number

Thanks! But you can actually just multiply the diameter by pi=3.14159265.
It is easier to do a roll out than get an accurate diameter measurement.

6. Originally Posted by shiggy
Most computers use the rolling circumference of the tire in mm or cm for the calibration number
It's just a matter of unit conversion.

Originally Posted by shiggy
It is easier to do a roll out than get an accurate diameter measurement.
I wonder if the difference matters... I'll try to experiment on that.

Thanks!

Thanks! But you can actually just multiply the diameter by pi=3.14159265.
My 2.2 inch Continentals have a larger outer diameter than my 2.35 Nevegals so I've come to the conclusion that those numbers aren't very accurate. Plus you'll have a different in outer diameter based on the width of the rim. A wider rim will create a larger outer diamater as well. The numbers on the tires aren't very scientific.

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