Tech FAQ: Crank Conundrum
Are there currently any 180mm 2×9 specific cranks on the market (besides Middleburn cranks, which use a square taper BB and have a reportedly flexy chainring-as-spider configuration)? I know that I could probably get by with a 26 inner 38 combo on a Shimano crank, but a double seems pointless if it doesn’t improve the chainline and allow me to use all nine cogs from each chainring. In that case, I’d rather run a 1×9. Is there a way to effectively set up any existing triple cranks to run as a double, or are we taller riders just out of luck for now?
As far as I know, there are none on the market. SRAM XX comes in only 170mm and 175mm length options, and that is with 26-39 (120/80 BCD), 28-42 (120/80 BCD), and 30-45 (120/80 BCD) chainring options. But there is at least one option you can cobble together. Although you will still have a “chainring-as-spider configuration,” you can use the 180mm Dura-Ace 2X9 setup that Travis Brown used a for the Leadville 100 this year by using the inner and middle positions of a triple Dura-Ace crank. See him using it in the new movie “Race Across The Sky” as well.
You should be able to find one of these cranks in 180mm, but if you were to do so, you would be limited to using a 30-39 combo. This is because a Dura-Ace Hollowtech triple crank has no threaded standoffs for the granny gear. Instead, the granny gear bolts onto the middle ring. The Dura-Ace Hollowtech triple crank is actually a double crank with a triple spindle and no inner steps on the spider tabs for the 39-tooth chainring. So the Dura-Ace triple’s middle ring is a 39-tooth with long tabs hanging down for chainring bolts to hold it to the 30-tooth. So it seems that a 30-39 combo would be your only choice, since those are the only rings I know of that Shimano made for that crank.
Here is what Travis had to say about it:
“The Leadville course — because of the altitude, grade, and length of the Columbine climb — is at the extreme end of necessities for a low climbing gear. That being said, you know I am a big proponent of even a 1×9 set up, and have been since I used that (1×9) setup for the entirety of the 2005 race season as an experiment. The drive train that I used in
Leadville was a 30/39 double, and as you say that is the only ring option for that crank set. Part of this choice was the option of a 180 mm crank. That was matched to an XX/Red rear transmission. The XX cassette as an 11-36 gave me a me a 21.6 inch low gear, which I used a lot on the Columbine climb (and the return Power Line climb) but it was manageable.
I think this combo is a great normal XC course set up, especially with the new 36t rear cassette option from SRAM in 10s and Shimano in 9s. Another advantage is improved chain line over most doubles, good front shifts due to the small, 9-tooth gap between chainwheels and lower Q-factor than any triple I have used save the old, very adjustable, three-piece design.
The biggest limiting factor with this setup is frame clearance. The 30t inner ring does not clear all frames in its stock configuration at the chainstay.”