Several of my fellow Fitzy teammates are considering racing a 29er this season and our team has some excellent options. In addition to frame options, the drive train is a major consideration. If I were building a 29er race bike today, I am not 100% sure what drivetrain I would choose so I decided to do a little math.
Before I geek-out to much, I have to come clean. I use my 22F/34R combo. There, I said it. I would like to think that I am getting stronger and could live with a 32 in the rear instead of the 34 but to this day I am clinging to the safety of my 34. And now that the sexy SRAM XX 2x10 speed is here, and other 2x9 drive trains are trying to compete, do they offer comparable gearing AND the advantage of crisp front shifting?
I plugged four current drivetrain options into the Sheldon Brown Gear Calculator and used my trusty 22F/34R combo as the baseline. Here is what I learned:
The numbers circled in red in the lower left corner represent gear inches in the "easiest" gear combo. The bigger the number, the harder the gear.
The 22F/34R combo is my baseline at 18.8 Gear Inches
The 22F/32R combo is 5.85% harder at 19.9 Gear Inches
The smallest front chainring you can get with SRAM XX is 26 and the largest available cog is a 36. The 26F/36R combo is 11.1% harder at 20.9 Gear Inches
The top-of-the-line Jamis 29er comes with a 2x9 drivetrain; FSA 27/42 crankset and a Shimano 12-36 cassette which results in a stout 15.95% increase over a traditional 22F/34R at 21.8 Gear Inches
The Felt Nine Team comes with traditional 22/32/44 in the front and an 11-34 in the rear
The Jamis Dakota D29 Team comes with a 2x9 drivetrain and is for fit riders who can push the 27F/36R up the steep hills
The Jamis Dakota D29 Pro offers a drivetrain with a larger-than-normal safety net; a 22/32/44 in the front and a 12-36 in the rear
The biggest eye opener of this exercise was the 11.1% difference of SRAM XX vs. my current gearing. When I am 9 hours into a 12 hour Cream Puff 100 race, could I really push a gear that is 11.1% harder? Some will argue that you will simply adapt, and therefore go faster, and that having the 22F/34R is a crutch. What do you think?
EDIT 3/31/2010: I am not building a new geared bike but I have been curious about the new SRAM XX. For now, I will stick with my 22/32/44 and my 11-34 in the back.