Drivechain messin’

6 05 2013

I’m in the process of re-purposing some bikes. My Brooklyn Machine Works Gangsta II is going to become a bona fide track bike. That means my old Voodoo Dambala had to be made into a town bike. This allows me to use 40c ish tyres as well: useful when the roads are still suffering after a couple of harsh winters and in poor repair.

I like my town bike having a fixed gear, but achieving this on the Dambala with a fairly large chainring isn’t straightforward. Chainstay/ring contact was an issue, which meant I had to put the ring on the outer tabs of an mtb crank. So, I pulled the crank from the Krampus which left me in need of another set of cranks for the big green machine.

I ended up getting hold of an XT m785 2 ring crank – it is much more aesthetically pleasing than the triple for a single ring set up. The problem is the chainline: at 48.8mm (which is the midpoint between the 2 rings), using a 34 tooth ring puts the chainring around 52mm out from centre, giving crappy chainline with a 9 speed cluster. The chainline on the middle of a triple HTII shimano crank is 50mm. So, I used some spacers to push the ring more inboard.

Of course, ideally, I would like the ring even further inboard. The actual real world chainline for a 9 speed shimano cluster on a 135mm OLD hub is ~45mm, but there is not enough clearance to move the ring in more than another 1mm or so without it getting eye wateringly close to the chainstay yoke. So, not ideal but better looking (in my eyes at least) and it works acceptably well.




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