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#1
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Installing "U-brake" bosses:
I'm building a fixture to braze on U-brake bosses to an existing
frame. A mandrel through the drop out is zero and the wheel radius is R. In terms of R, how far do I offset for modern brakes? Jones |
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#2
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Installing "U-brake" bosses:
On Aug 16, 5:30 pm, !Jones wrote:
I'm building a fixture to braze on U-brake bosses to an existing frame. A mandrel through the drop out is zero and the wheel radius is R. In terms of R, how far do I offset for modern brakes? Jones I haven't done this and don't have any frames or brakes in front of me to measure, but I will give it a shot since you haven't gotten any replies. First of all, understand that there aren't a lot of folks in BMX, yes even brake designers, that are completely on the ball with numbers and details, so you really should just measure the brakes you're planning on using. From looking he http://www.tektro.com/02products/12fx30.php and also having my buddy measure an Odyssey Evo2 over the phone, it seems like most brakes max out the reach at around 44-48mm. The 907A on that page is probably the single most commonly specced 990-style brake and their measurement is 30-47mm. The Evo2 measured around 35-48mm. A quick search of the framebuilder's list ( http://search.bikelist.org/getmsg.as...10602.0049.eml ) mentions using an axle-to-boss dimension of 9 1/8" (231.775mm) with a 406 wheel all the way forward in the dropouts. That number would make sense alongside the brake reach numbers I mentioned. It might also be worth noting that any well-thought-out standard axle- to-boss dimension used by folks who make BMX frames is going to take into account both the large range of rim wall heights that a bike might run, the amount of axle adjustability offered by the frame, and whether the brake will be SS or CS mounted. So if this was, say, a bike with vertical drops and no possibility of chunky rims, then just using someone else's numbers but adapted to whatever wheel size you're using may be less than optimal although it will probably work. |
#3
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Installing "U-brake" bosses:
On Aug 17, 9:11 pm, Nate Knutson wrote:
On Aug 16, 5:30 pm, !Jones wrote: I'm building a fixture to braze on U-brake bosses to an existing frame. A mandrel through the drop out is zero and the wheel radius is R. In terms of R, how far do I offset for modern brakes? Jones I haven't done this and don't have any frames or brakes in front of me to measure, but I will give it a shot since you haven't gotten any replies. [...] Very useful advice! Thanks! Jones |
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