Bike Forums > Tire size conversion help
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 09-16-08, 03:14 PM #1 acuteot Newbie Thread Starter   Join Date: Aug 2008 Bikes: Trek 7.2 FX Posts: 3 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Tire size conversion help Hi everyone, I'm a newbie biker, and I just bought myself a new computer (even managed to install it with no problems!). I'm trying to figure out what my wheel factor is. I have a Trek 7.2 FX and it says that I have a wheel size of 700 X 35C. The data point I need to enter is the wheel factor, or the distance in millimeters per one turn of the wheel. Per the instructions, a 700 X 32C has a wheel factor of 2155, so I'm assuming that it will be just a bit higher than that. Any help would be greatly appreciated.
09-16-08, 03:34 PM   #2
cyccommute

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Quote:
 Originally Posted by acuteot Hi everyone, I'm a newbie biker, and I just bought myself a new computer (even managed to install it with no problems!). I'm trying to figure out what my wheel factor is. I have a Trek 7.2 FX and it says that I have a wheel size of 700 X 35C. The data point I need to enter is the wheel factor, or the distance in millimeters per one turn of the wheel. Per the instructions, a 700 X 32C has a wheel factor of 2155, so I'm assuming that it will be just a bit higher than that. Any help would be greatly appreciated.
That's about right for a 700C x 32mm. You won't be off by much. If you really want to be accurate, get on the bike, mark the tire with something and ride in a straight line until the mark shows on the pavement. Measure the distance. Perhaps do several tests and average the results. But I'll bet they come out around 2160 +/-0.5
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 09-16-08, 04:46 PM #3 Bill Kapaun Senior Member     Join Date: Feb 2007 Location: Mid Willamette Valley, Orygun Bikes: 86 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. Posts: 9,886 Mentioned: 1 Post(s) Tagged: 0 Thread(s) Quoted: 305 Post(s) Your tire diameter would be 6MM more, so that times PI would be about 19MM more. I just "lasso" my tire with a string, and measure the string. Even if you are off by "a few" MM, remember that's in over 2000 units. 20 "parts" off is only 1%, which is far more accurate then your car!
 09-16-08, 04:52 PM #4 acuteot Newbie Thread Starter   Join Date: Aug 2008 Bikes: Trek 7.2 FX Posts: 3 Mentioned: 0 Post(s) Tagged: 0 Thread(s) Quoted: 0 Post(s) Thanks for your help! The exact number is 2173.8, so 2174, I had initially but in 2175, so I got pretty close!