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NeoRetroGrouch
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6,491 Posts
Discussion Starter · #1 ·
Can somebody give me a good number (or point to a source) for the outside tire diameter with a 650c rim and a Michelin Pro Race tire. I don't have the wheels built yet and I need to do the Junior gear inch calculations.

Thanks,
TF
 

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Arrogant roadie.....
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4,232 Posts
OK, since you are asking about diameter (not circumference), it's really quite simple to do. Take your rim diameter (I believe that the previous poster got at least that part right), which is 571mm. Add to that 2*the tire "width" (from the ERTRO # on the tire), and you have the diameter. If your tires are 21mm, then you have 571+(2*21)=612mm.
 
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