Question:
Compatibility Question for Mr. Manic… I understand that SRAM and Shimano derailluers are not interchangeable because of the amount of cable the shifters pull, and the resulting movement of the parallelogram linkage in the derailleur, right? But what about using a 10-speed SRAM shifter with a 9-speed SRAM rear derailleur? Mountain doubles make so much more sense to me, but I don’t want to spend my hard-earned cash for a new derailleur if the old one can be made to work.

Answer:
Right on. If you’re looking to simplify your life, a double chainring configuration is a good start. Only three things in this world are worse than a mountain bike with a triple chainring crankset: cannibalism, Russel Brand, and a road bike with a triple (in that order). Unfortunately, you can’t substitute a 9-speed SRAM rear derailleur for a 10-speed model. I know it seems like you should be able to do this, but, according to SRAM, the “Exact Actuation” leverage ratio found on all their 10-speed rear derailleurs is actually different from the “1:1” ratio used on 9-speed derailleurs, so trying to mix those up would lead to the same kind of shifting problems you’d encounter if mixing SRAM shifters and Shimano rear derailleurs. Even though the shifter is the brains of the operation, telling the rear derailleur how much to move for each shift, the leverage ratio on the rear derailleur ultimately determines how to translate those increments, and the 9-speed derailleurs don’t use the same ratio as the 10-speeds.

If making the move to 10-speed all at once is a bit much (now that rear derailleurs cost more than many bikes), consider going with a 9-speed double ring configuration. Most 11-34t 9-speed cassettes offer a pretty broad range, and it turns out companies like Blackspire offer chainrings purported to work with both 9 and 10-speed systems and available in hip, dualie configurations, like a 26-tooth inner ring and a 38-tooth outer. Once your ship comes in, you could buy a 10-speed rear derailleur, rear shifter, chain, and cassette, and become what historians call “contemporary.”