's Forum Archives - Components

Archive Home >> Components(1 2 3 4 5 6 7 8 9 10 )

Does a 700c x23 wheel have a diameter of 70 centimeters?(5 posts)

Does a 700c x23 wheel have a diameter of 70 centimeters?Crown Jewel
Jun 21, 2001 8:04 AM
Instead of rolling the tires on my bicycle to measure the circumference of the tire, I thought about simply computing it. So, if a 700C x 23mm tire has a diameter of 700mm or 70 cm, then the circumference will be (700) x (3.14), give or take a few millimeters.

I am looking for this information to enter it in my computer.

Thank you,
Not quite...Cima Coppi
Jun 21, 2001 8:52 AM
70cm is the diameter of the rim, not including a tire. So a tire will add some more cm to that diameter. You can still measure the diameter and computer a circumference as you stated above. Or if you're trying get an accurate circumference for a cyclometer, your best bet is to sit on the bike and roll it one full wheel revolution to get the circumference.
All tire dimensions are imaginary...cory
Jun 21, 2001 9:47 AM
Only thing I've found that's fairly consistent is the diameter of the tire at the bead, and even that varies a little (some tires are hard to mount, others slip right on). If you measure the width, height or anything else, though, you'll find wide variation. Rivendell's new 700x27 Rolly-Poly tire is taller than most, for instance, but almost a true 27 mm wide. Avocet and Panaracer 32mms are shorter but only about 25mm wide. Most accurate way I know to calibrate a computer is to sit on the bike and roll one revolution of the wheels with the tires you'll be riding.
Not that simple...Don in OKC
Jun 21, 2001 11:28 AM

The tire height varies from one manufacturer to another even within the same tire size: ie 700 x 23. Then for purposes of calibrating a bike computer, the weight of the rider (another variable) compresses the tire, reducing the diameter. And to get downright picky, the amount of air pressure will also have a small effect.

This is why most riders do a roll out while sitting on the bike to get a circumference measure. Then you've got an accurate number to calibrate with.
You're off by 5%Kerry Irons
Jun 21, 2001 6:12 PM
For at least Conti GP and Michelin Axial Pros inflated to 120 and 110 psi respectively, and a 180 lb rider, the diameter of a 23mm tire mounted on a "700c" rim is 667mm. YMMV