Canti brakes-equipped bikes - 650b conversion

[weisan]

normal 700c bike running on canti brakes typically run into issues when doing the conversion to 650b because of the brake placement. Wonder if anyone has managed to find a way around that problem. Thanks!

[Cicli]

Depends on the frame. There is likely no way around if the brake bosses are right next to the brake track. Just no way to get any leverage when the pivot and the pad are in the same place.

These are for BMX frames but????? http://elevnracing.com/products/brake-adaptators/

[blakcloud]

Not my photo but they seem to work. The only caveat is you need removable studs on your current bike. Not all cantilever studs are removable.

[Ed-B]

A 700c cantilever bike is difficult to convert to 650B due to the close proximity of the canti bosses to the 650B rim. These brake extenders can be used on frames that have removable canti studs, but that will only get you part of the way there. You still need the right brakes, and then you need to deal with the fork.

I just finished doing a 650B conversion on an aluminum cycloross bike. I used the Promax brake extenders in the back as shown on the bike above, The mini-v's shown above will work with the extenders, but I chose to keep cantilever brakes for my bike.

These extenders were originally conceived to raise the cantliever boss. But flipping them upside down and left to right provides just about enough drop to reach a 650b (584mm) rim on a frame built for 700c (622mm) rims. There's no room for hardware on the backside of the brake because the upside-down extenders are flat up to the original cantilever mount. Anything in the back of the brake will bind on the extender. So the trick with these is to use a brake that has all of the hardware in front of the base of the brake.

The carbon forks commonly found on modern bikes are a different story, however. Many of them have smaller stud threading, and the three spring holes are typically just a flat piece of stamped steel that is simply held in place by the stud like a washer. The extenders won't work here, they need the right diameter stud and a set of fixed spring holes to hold them in place.

For my bike I used a Bontrager Satelite Plus carbon road fork in the front, it has the same axle to crown as the original canti fork. Right now I have a Tektro 559 brake in front, but I'm looking into fitting a bmx u-brake on a 990 plate which may have better stopping power. That incremental upgrade is still un-proven, but the bikes works really well as it sits now.

Ed.

[weisan]

Thanks for contributing to this discussion, I was hoping you would. That was very helpful especially with the closeup pictures. I was leaning in the direction that you did and you confirmed my hunch. I have the Satelite fork as well so maybe I will swap it out and give it a try.

[Ed-B]

Originally Posted by weisan

Thanks for contributing to this discussion, I was hoping you would. That was very helpful especially with the closeup pictures. I was leaning in the direction that you did and you confirmed my hunch. I have the Satelite fork as well so maybe I will swap it out and give it a try.

I was thinking that I needed to post a follow-up, and your post is a good stimulus.

Having that Bontrager fork is the only thing that made me decide to pursue this conversion. It wasn't going to work with the stock fork. If you have the Satelite fork I'd say go for it!. I'll keep you posted on the bmx u-brake experiment. I have the 990 plate, and the brake is in the mail...

But for anyone else I would say that unless you have almost everything you need to complete a 650b conversion on a cantilever rim brake bike that you should just forget it and go out and buy or build a disc brake 650B machine with mountain bike wheels. It's easier, it's not much more expensive, and ultimately you will have a better bike.

Ed.

[Ed-B]

The bmx u-brake/990 plate combination isn't going to work on my Bontrager Satellite fork with 650B wheels. The pivot studs are set too far apart for a reasonable reach to the 24mm rim using v-brake type pads with the spacers set at their widest arrangement. If there was a 990 plate with a narrower stud spacing it might be a good match. There's more brake reach than necessary, also, so the pads would be at the top of the slots. It's just too much brake for this application - too wide and too deep. A custom plate would be ideal, and probably not too difficult to make if you had the equipment to do it.

Actually... Now that I look at this plate I think it might be possible to drill and thread two new holes up higher and closer together... The studs are threaded and lock-nutted onto the plate, so they could be relocated to a better position for this fitment. It would probably look like a hack, though. :-)

I'll keep playing with this, but for the time being I'll use the Tektro 559 dual pivot caliper. I fit a set of Kool Stop Dura2 salmon pads in the holders on this caliper, and the performance is quite good!

Ed.

[weisan]

Thanks for the follow up, Ed pal.