tkm

As title states. I did a roll-out test, but I'd like a more exact number on a 29x2.2 tire, if anyone has it (obviously for my bike computer).

Tried google and couldn't find anything concrete. And the formula I found put me way off from what I think it should be.

I did find a 29x2.3, which is 2350mm. But nothing for 29x2.2.

Thanks.

JiveTurkey

Roll-out will be more accurate than some calculation based on theoretical numbers, but here goes:

Diameter of rim at bead seat = 622mm
Width/height of tire = 2.2 in. * 25.4 (mm/in.) = 55.9mm
Circumfrence of tire = 3.14 * (622 + (2 * 55.9)) = 2304mm

C Law

As J T said above, how are you going to get more accurate than a rollout?


Besides, every supposed 2.2 tire is different.

dirtbikedude

For the bike computer the roll out is what you want to use as that will be the "true" distance the tire travels.

If you are that anal that a cm or two will throw you off (cyclocomputers are not that accurate anyways) then you could even have a friend help you, have him mark the tire/ground then you sit on the bike with feet on the pedals since the "squish" of the tire will change the distance as well, then roll until the mark comes back around and have your friend mark the ground again.

deraltekluge

Make sure you go in a straight line, and go for a few revolutions of the tire if you want real accuracy.

Of course, if you really, really, really want accuracy, you'll have to do your measurement on the same surface you'll be riding on. Especially with a mountain bike tire, where the tread would dig into dirt and reduce the rolling diameter and circumference from what they'd be on pavement.

Do you actually need that sort of accuracy??

tkm

Thanks for the numbers. My roll-out was 2315mm, so +/-11mm isn't too bad.

I don't *need* that kind of accuracy, but I want to get as accurate as possible; there is no reason not to. But it is good to know I'm within a theoretical range of what a 29x2.2 should be. I'll probably settle on 2310mm to split the difference.

Funny part is, the LBS said that my Trek Insite 6i computer wouldn't work with a 29er. However, I'm able to punch in the specific mm's without problems. I assume it'll work fine.

DirtPedalerB

I would think cyclocomputers would be one of the most accurate measurement of distances(way better than consumer GPS). especially if mounted on the back wheel. Look how they measured stuff for years, with a measuring wheel, which is just a cyclocomputer on a stick.