# Thread: Millimeters per revolution of bike wheel?

1. ## Millimeters per revolution of bike wheel?

I have a 17.5 inch bike wheel, and I need to figure out the "distance in millimeters per one revolution of the bike wheel" for programming a bike computer, according to the manual. I am not sure how to go about this. I tried figuring out the circumference of the wheel in mm, but the number was too big (the manual includes lengths for 20"-27" wheels, and the number I got was way too big.) Any help?

2. ## Re: Millimeters per revolution of bike wheel?

Originally Posted by ftbtef
I have a 17.5 inch bike wheel,...
Is that radius, or diameter, or circumference?

1 inch = 25.4 mm

Now ask your question again: doesn't make much sense the way it's worded;
a "manual" has nothing to do with math...unless used to set boundaries...

3. ## Re: Millimeters per revolution of bike wheel?

Since bike tire size is usually given as the diameter, I reckon we can assume your bike has a 17.5 inch diameter tire.

Therefore, it is $17.5{\pi}\approx 55$ inches in circumference. That is the distance in one revolution.

How many millimeters is that?. Multiply 55 by 25.4 and get about 1396.5 mm

Convert the 20 and 27 inch the same way. $25.4{\pi}D=\text{distance in one revolution in mm}$, where D is the diameter of the tire.

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