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View Full Version : wheel circumference...please help.


Ozz
03-07-2005, 04:52 PM
yeah, I know the formula....but I am looking for a number (in millimeters) to calibrate a bike computer.

What numbers do you all use for a 700 x 23 Conti GP 3000?

I am basically too lazy to lay a string on the floor and roll my bike along it. I am also too embarassed to ask my wife to help me while I sit on the bike so the wheel is properly loaded. Cuz as you all know, the circumference is less when you have a load on the wheel. Note: Special thanks to "keno" for helping me thru that particular math problem.

I am sure there are some very anal people on this forum who have measured their 700 x 23 tires circumference to 0.5mm with a 180 lb rider on the saddle. These are the people who have the number I seek.

I currently use 2145mm 'cuz that is the number that came in a manual I had for an old computer. It seems to work pretty well, as I get the same reading as the radar operated "please slow down" speed indicators that seem to be all over my neighborhood. How close am I?

Thanks for your help.

Spicoli
03-07-2005, 05:08 PM
If I remember correctly I used to use 2120, but I am going on memory. I am pretty sure thats it and I know I have it written down someplace, if I find it I will tell you for sure. Also that is for GP 3000's. Hey if worse comes to worse go small and let yourself think your going faster than you are!!!

Smiley
03-07-2005, 05:20 PM
Ozz , measure the radius in mm and the circumference is (2)PIE(R) or better said its 2 times 3.14 times the radius in mm .

Ozz
03-07-2005, 05:27 PM
Ozz , measure the radius in mm and the circumference is (2)PIE(R) or better said its 2 times 3.14 times the radius in mm .
You want me to do the math? :cool: Dude, what are friends for? I'm looking for someone who has already has the number....

Besides, measuring the radius is mucho difficulto ("muy dificil" for you speakers of espanol) while sitting on the bike...again, do not want wife to mock me for this aspect of cycling...she already thinks I'm weird.... :D

weisan
03-07-2005, 05:35 PM
http://www.sheldonbrown.com/cyclecomputer_calibration.html

Dave
03-07-2005, 06:15 PM
That's what I've been using for years. Could be a little less if you roll the tire out while sitting on the bike.