Im currently selling ssome cranks on eBay and have been asked what the BCD is. I have never heard this term before an have no idea what it means! I have looked on Sheldon Brown, but im still no more clued up as I was before.
[url= http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200621990739&ssPageName=STRK:MESELX:IT#ht_500wt_1156 ]These are the cranks if that makes any difference?[/url]
Thanks
Chris
Bolt Circle Diameter.
measure centre of BB axle to the centre of a bolt hole and double
if you drew an imaginary cricle from the centre of the crank that went through the middle of all of the bolt holes that's the Bolt Circle Diameter.
Most MTB's are 104mm BCD
they are 104mm. its the distance from the centre of a cainring bolt hole to the next one on either side.
Or measure the centre-centre distance of 2 adjacent bolt holes and look up the BCD on this chart:
http://www.sheldonbrown.com/gloss_bo-z.html
charliethebikemonger has the dims, along with easier to measure - hole to hole dims, on his site.
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Measure from one side of the hole to the same side of the opposite hole. If there is five holes then see sheldon!