Sunday, November 20th, 2011
Some commuters are unstoppable, and our friend Matt was going through two chains a year commuting in snowy, slushy, salty and gross western Connecticut winters. He had the weather-proof solution: an 11 speed Alfine internally geared, belt driven, disc-braked super commuter, and I’m psyched he asked us to build it for him.
I’d done one belt drive before, a single speed, but the Alfine hub, coupled with the desire for fat tires, creates some new technical challenges. Belts are wider than chains, but more importantly they need to run perfectly straight – if not the belt will literally walk off the cog or sprocket. [This is one reason for the new Center Track system, which allows for more flexibility]
Even with chain drive, providing clearance for chainrings and wide chainstays can be a problem. Here, it’s worse – the belt is wider, the “belt line” has to be perfect, and to top it all off, the rear cog on an Alfine hub is set in away from the dropout, to accommodate the shifting cable. I did some fancy crimping of the chainstay, so here it is, built up with 26×2.3 tires, ready for action:
Here are some shots of the build in process:
When Matt and I began discussing this bike last year, we weren’t sure how best to break the frame (the belt doesn’t come apart, unlike a chain, so you have to be able to get it inside the rear triangle). Fortunately, Paragon came out with a belt option for their sliding dropouts. These are great for disc brakes, because the caliper stays aligned to the dropout, and for belt drive systems, as they have integrated tensioners. Belt tension is super important for proper performance. Here are some shots of the dropouts during construction, and of the frame before components. You can see how I weld on a section of tube, similar to how we do capped stays:
And here are some shots of me mocking everything up before the wheels were built:
And some of the completed frame. The Paragon dropouts are stainless, so I was able to polish the interface where the frame breaks:
And some more shots before components. Note, the bottom bracket below is just one I had lying around that I used to determine the alignment; in the complete bike pictured above, it’s a narrower Phil that fits properly.
Next up: Belt drive again, this time a single speed! And super-lightweight S3 tubing fever! Weld-o-Rama 2011 continues!