General Cycling Discussion - Cycle computer settings, 207,210?

When I setup my cycle computers I always end up resetting the "circumference number" a little lower than the recommended tire size. if I set it normally, by the instructions table, it seem to give to "high" of a distance/speed reading....

Any comments?

I do the measuring and then set the wheel circumference
that way. Seems to be a bit more accurate that way.

Marty

I measured my tires and set the size on the dot.

Originally posted by Richard Cranium
When I setup my cycle computers I always end up resetting the "circumference number" a little lower than the recommended tire size. if I set it normally, by the instructions table, it seem to give to "high" of a distance/speed reading....

Any comments?

Yup, I'd stick with your measurement. Also, you should put weight on the bike when doing this measurement as the rider's weight will compress the tires a bit. Then, as a check, take the cage (auto) out and measure an exact 5-mile distance and check it with the bike. Then ... adjust accordingly.

If you're referring to the numbers in the manual, the correct answer isn't in your poll.

The correct answer is: do several rollouts to get the true circumference of your tire at normal pressure with you on the bike. Use the average and input that number.

The numbers in the manuals are by necessity only crude approximations. They can't know what brand of tire you use, how much pressure is in it, or how much you weigh.

RichC

I measured once with my weigth on the bike - this time it matched the manual. I wouldnt mind if it was off a bit, because I am only interested in how my speed or distance compared with my other rides. I am not trying to get my performance into the Guiness Book of Records, so the exact numbers dont matter.

yep I measure the wheel roll i get pretty accurate readings comparing it to an automobile spedomitor ? i have seen more than a few auto speedomitors to be off too right from the factory. I think it is a scam to make you use up the warentee miles quicker
CF

Well that was a true "Richard Cranium" poll, the poll was supposed to ask weather you used the "table" supplied with computer.

However the other answers still apply. Is the number you use higher or lower, or on the money (the table value).?

Most computers use the fornt wheel, I can't beleive there's enough "tire flattening" to create much error....never mind..

I know that Cat-eye Mighty 3's are "mighty" generous with their speed values........distance values....

Using 3 roll out average (with rider on bike).
2 different computers and bikes, both 20 inch wheels.
Bike 1 daughters (9 years old) Childs Mtn Bike with knobby tires, about 1/8 inch less than the 20 inch setting in the manual.
Bike 2 my LWB 'Bent with street tires, 3 1/4 inches LESS then the 20 inch setting in the manual.
Both manuals had the same 20 inch setting.

I measure to get as close as possible. That´s me:p

Anders K

Get it close enough and just ride....that's my theory :p