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stupid question...(9 posts)

stupid question...MPH74
Jun 5, 2003 2:48 PM
what does the 700c mean with regards to road tires? centimeters? circumference? is it a measurement of the diameter in centimeters? please help!

i know that the 26 in mtn bike is the diameter in inches...
re: stupid question...Spoke Wrench
Jun 5, 2003 2:53 PM
700 refers to the theoretical tire diameter in millimeters.
c is a measure of rim width as in a, b, c, or d just like shoes.
re: stupid question...MPH74
Jun 5, 2003 2:57 PM
i think it just hit me.... it seems to be the diameter of a tire in millimeters.

so that being said, if you multiple 700mm * pi that should yield the circumference, right? i hope i'm remembering that formula right... so the circumference of most road tires is 700mm*3.1415926 = 2,199mm

is this right? is this then the distance that the tire will roll if inflated to the max psi? is the 2199mm the circumference of the outer most piece of rubber of the tire? would this be much less with the weight of a rider and the rest of the bike?

if anyone is wondering, i'm trying to program my new HR monitor!
re: stupid question...My Dog Wally
Jun 5, 2003 3:08 PM
I think your formula is slightly wrong. To calculate circumference, you'd use pi x radius (not diameter) squared. The radius is 350mm.
Circumference is Pi x DChen2
Jun 5, 2003 3:21 PM
The only reliable way to measure a bike wheel circumference is to pump it up to riding pressure, mount the bike, roll it on the floor with total body weight on the bike and have a friend measure the travel distance. But setting a computer with a more accurate working circumference can be done by riding the bike a known distance, like a mile, and then adjusting the circumference calibration until a mile is a mile.
forget all thatjtolleson
Jun 5, 2003 4:29 PM
though your question about the "c" isn't stupid at all.

You don't want to program your HR based on theoretical estimates of tire/wheel size. You need to actually either ride a distance that you are absolutely sure of (like a track, or some folks trust mileage posts) or roll the tire out over a marked distance on the floor.

Input the actual # from YOUR fully inflated regular tire.
re: stupid question...MPH74
Jun 5, 2003 2:59 PM
but i'm still confused what the "c" after the 700 stands for...
It means "C" this post from Monday. . .js5280
Jun 5, 2003 3:18 PM
In all things bike related, check Sheldon Brown...Brooks
Jun 5, 2003 3:19 PM
explanations of wheel sizes are here: