Ask BikeHugger: Disc Brake Conversion


Well, Daryl, the one that seems to be the best is made by Therapy Components. The Brake Therapy adapter connects to the frame at the left cantilever brake boss and at the hub between the left dropout and the hub flange. The hub will require a modification at the axle to allow the adapter to fit, and so not all hubs will work. Therapy has a nicely illustrated site explaining how it works.


p> photo from Bike Magazine



If that seems too inelegant for you, maybe you’d rather consider modifying the frame to directly mount a disc brake caliper, which means some serious mods. Ready? Let’s begin…

Is the frame material carbon or aluminium?

If yes, then the frame mod project stops. Aluminium generally requires some post weld heat treatment to return strength to the heat-affected zone. Even then, you’re not likely to find a reputable framebuilder willing to do the mods. Carbon is a tricking material for making modifications like a disc brake mount; it’s like putting a Corvette engine in an original VW Beetle. It could be done by one of those incorrigible types who also like to build their own sailboats in their garage, but it’s stupid and impractical.

Is the frame steel? Steel is generally the easiest material to modify as well as the material that most small framebuilders use. And you want a framebuilder to do these mods; if you were otherwise capable of doing it yourself you wouldn’t be asking me this question in this forum. A good frame candidate for a disc mount mod would have stout seatstays that don’t cant inwards too dramatically above vertical dropouts. The stoutness will resist heat damage from the brazing process and will better resist the forces applied through the disc mount. The more parallel the seatstay is to the plane of the wheel, the easier it will be to align an IS disc mount.

If the frame is titanium, it might also be possible if the same conditions of dropouts and seatstays exist. However, titanium must be welded not brazed, and there is far greater chance of post-weld warpage complicating the mod. All surfaces in the heat affect zone (HAZ) must be immaculate during the welding because even a tiny amount of oxygen or outgassing grease can embrittle the metal and ruin the project. Since at least some of the welding will be on a tube rather than a plate dropout, it will be important that the tube interior be devoid of any grease and be back-purged with inert gas for the TIG-welding. A bike that has an aluminium seat tube insert to bring the inner diameter of the seat tube down for the seatpost might block access to the vent holes for the seatstays.

Finding a framebuilder willing to do these mods might not be instantaneous. Done right, a mod like this may require a lot of time and set-up; conversely no one wants to pay for a skilled American artisan to do the work for more than what one can buy a mass-produced frame from Taiwan that already has the proper mount. But maybe you’ve got a frame that has the perfect geometry for you and a disc-mount would allow to use the latest components; it could be an awesome project. Don’t forget to budget for a new paint job.

Just don’t buy some cheapo frame off of eBay and think that you can get a disc tab welded on for $50. So that $150 Brake Therapy is looking like a bargain.

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