March 21st, 2009

For our friend Eric we’re building the first belt-drive Circle A. When we get all the components sorted out, I’ll be talking about how (& how well) it works, but first there are some oddities that we have to address when building the frame.

The first is that, because unlike a chain you can’t add or remove links and thus easily change the length of the belt, you have to determine a precise length for the chainstays that takes into account cog size, “chain” ring size, and belt length. Eric wants a single speed, so we had to be sure that the he was going to be happy with the gear ratio – there are some other combinations that will work (we used dropouts with extra-long slots), but it’s much more limited than with chain drives. Fortunately Gates, who makes the drive system, provides a spreadsheet that helps you determine the chainstay length.

But the real challenge, and related to the above issue, is that because the belt doesn’t come apart, the frame has to. WHAT?! I know. It looks a little something like this:


Now you can get around this issue with an elevated chainstay, like on all those old Haro and Nishiki mountain bikes from the early 90’s. But Eric wanted a classic looking lugged frame, so I wanted to make the disconnection as svelte as possible. Using our own dropouts, laser cut next door in Pawtucket, I modified an old seat stay end to become a detachable dropout/stay interface:

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Eric and I are working out the Yellow Cab themed paint; I’ll post pictures of that and the components as they arrive.

Speaking of Nishikis, I repainted one for Miguel in Austin. We saved the chrome on the dropouts and painted it a deep pearl blue:

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And finally I just started a touring bike for my friend AJ, I’ll start brazing next week. He’s using Richard Sachs lugs and all True Temper tubing. Note the dimpled chainstays to give him some more tire clearance:

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Next: more belt drive action!

This entry was posted on Saturday, March 21st, 2009 at 7:51 am and is filed under Bike Building, Bike Painting. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.


  1. Chris Bull says:

    January 29th, 2012 at 5:57 pm

    […] tricky thing about single speed belt drives, as discussed before, is that you have to be pretty certain about what gear ratio you want. I have to calculate the […]

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Circle A Cycles   |   523 Charles Street   |   Providence, RI   |   401.831.5221
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