Originally Posted by
Barrettscv
With a 50 & 46t chainrings, the incremental spacing on the rear freewheel or cassette should be about 20%. Consider finding a 13-15-18-21-24-32 freewheel. IRD makes this freewheel, it's available from Harris Cyclery.
The increment between the 50 & 46t chainring is 9%. The cog spacing should have double the increment that the chainrings have.
Run your gearing through the Sheldon Brown Gear Calculator:
http://www.sheldonbrown.com/gears/
Michael
A freewheel based on a 1.20 factor would ideally be 13, 15.6, 18.7, 22.46, 27.0, 32.4, for a practical design of 13, 16, 19, 22, 27, 32. The IRD is not a perfect match. To see the exact comparison we'd have to look at the resulting gear steps with the IRD and the practical 1.20 freewheel, also comparing to the 13/29 I came up with. That would settle what's better from a half-step rules point of view.
But the biggest limitation in all this is that it's rare to find anyone anymore with a selection of cogs you can use to build the freewheel you would most like to have. The best we can do is find a freewheel that is as close as possible to a decently even spacing, then play with the numbers to see what chainwheels could work. If its not too closely spaced, get those chainrings and put them on a triple with a granny ring.
CMC is way ahead of the game owning that 14-27 freewheel, which is already very close to even spacing. He just needs to go up a tooth on the small chainring, then he will have a very good half-step pattern.