Singlespeed & Fixed Gear - how to measure bolt circle on chain ring?

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highpants
02-26-06, 05:19 PM
i bought a campy chainring at the swap meet today here in minneapolis, but didn't buy cranks because i couldn't find any 165s. now i've got this chain ring and i'm sleuthing around on the internet, but have no idea what size the bolt circle is or which cranks are going to be compatible with it. if worse come to worse i can bring it into the shop and see what they have that might fit it, and hope that someone says, "oh, that's clearly the blah blah blah", but i thought i'd check here first.

12XU
02-26-06, 05:23 PM
http://www.sheldonbrown.com/images/measure-bcd.jpg

Multiply the number by 1.7 and you have your BCD!
highpants
02-26-06, 05:26 PM
thanks, i love bike forums.

highpants
02-26-06, 05:28 PM
i get 136 when i follow that formula, but i'm not sure if that makes any sense.
baxtefer
02-26-06, 05:30 PM
i get 136 when i follow that formula, but i'm not sure if that makes any sense.

they're 135's - campy standard for road rings.
highpants
02-26-06, 05:34 PM
that does make sense, as there were some very low priced 170mm chorus cranks that i probably should have bought for $65. i was worried about my short wife and the low BB on her bike. guess i blew that.
poopncow
02-27-06, 07:01 PM
135mm indeed. you can also find a nice look up table for BCD/ hole to hole measurement on the branford bike website.

note: my mentioning of the site is for info and reference material, not as an indorsement of their products.
Moochers_Dad
02-27-06, 07:07 PM
Here's Sheldon Brown's page with a lot more information:Sheldon Brown's Chainring page (http://sheldonbrown.com/harris/chainrings.html)