Should be a fairly simple exercise in trigonometry for any given number of spider arms, provided that the arms are evenly spaced, which is the case for every bicycle crank I've ever seen. I don't really feel like reviewing sines, cosines and tangents today though. Maybe someone else has worked this out more recently.
Regards,
Jerry Moos Houston, TX
Sheldon Brown <CaptBike@sheldonbrown.com> wrote:
David Feldman asked:
>To the mathematicians on the list--is there a formula
>for calculating BCD from bolt-to-bolt distance?
Sure. For 5-bolt systems, multiply by 1.7
This and many other bicycle questions is answered in my online Bicycle Glossary.
The relevant entry is at http://sheldonbrown.com/
Sheldon "http://sheldonbrown.com/glossary" Brown Newtonville, Massachusetts +----------------------------+ | Lend me ten pounds, | | I'll buy you a drink | | --Shane McGowan | +----------------------------+ -- Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com Useful articles about bicycles and cycling http://sheldonbrown.com