Use these bolt spacings to identify your crank's pcd and smallest chainring.
For other 4 bolt cranks: pcd = 2 × bolt spacing.
The minimum size of an Oval depends on its ovality - it is greater for ovalities more than 20% and smaller when less than 20%. The minimum number of teeth for 6-bolt cranks may be estimated as follows:
minimum Oval = minimum round 1 - ( 0.0025 × ovality )
© Chris Bell