rm -rf

Here's Mike Sherman's gear calculator, with 39-53 and 11-28 10-speed. It pops up a notice that you can save the URL to keep these settings as a favorite/bookmark.

You can make changes, and the charts update on the fly, so try different chainrings and cogs to see how they would work. The Speed over RPM Range chart, with each chainring in a different color, and the Speed at 'X' RPM chart at the bottom are the most useful.

See how it works at the usual speeds and cadences that you use. For a tri or time trial, it would be good to have gear combinations with small differences at the usual flat road speeds, to get just the right cadence.

And change the chainrings to 34 and 50 to see what difference that would make. Or make it a 39-50-53 "triple", and you can compare the 50 and 53 directly.

At 90 rpm:



39-50-53 on one chart. The 53 is about 1 mph faster for the same cadence at speeds near 20 mph. Not a huge difference.