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BMX Disk brakes
What about them?
Thursday gets asked about putting disk brakes on BMX bikes every season. Mostly by kids... "Brakes? What are brakes?" Well, every question starts a train of thought ... like, why not? The only disk brake bikes you see at the track have these mount gizmos that bolt over the rear axle and travel with it, maintaining your alignment. Well, picture a brake rotor and caliper .. if the rotor moves a half inch away from the caliper it takes a serious piece out of the pad contact area. But what if the rotor moved along the caliper?
Thursday popped for a LX rear brake set from the big S and a half dozen braze-on mounting tabs. It was all trial and error. As it turns out, the mounting tabs are canted enough that when you braze them on a set of BMX stays, the caliper is more-or-less parallel to the dropout slot. That means in turn that you have about an inch and a half of axle positions where you get decent pad contact with the rotor. That's provided you position the mount just right. An added bonus of this setup is the brake mount brazes up to the dropout, making for a real stiff, solid mount.
Be aware! Not all disk brakes mount the same. The key to a successful mount is the adapter that allows the caliper to be bolted to an ISO tab mount. Some adapters do not tilt the caliper far enough forward. The (unfortunately now discontinued) M515-LA cable-operated disk brake had the rearward mounting hole far enough below the forward one to get the caliper more-or-less parallel with the rear dropout slot.
Another brake that seems to work is the Avid BB7. If you plan on using your own disc brake, check the drawing below to see if the adapter on your disk brake is in the ballpark.Thursday recently got a few sets of disk mount tabs from Kirk Pacenti that have slotted mount holes. These are extra-cost items, but if you are the type who just has to fiddle with things, this will allow you to adjust the caliper location precisely to the disk rotor. I will post a photo when I do up a frame with these mounts.
Thursday did not formerly recommend a juice brake for BMX use. But, once you use them, you know you gotta have them, somehow. Problem solved! The same internal routing available on the 4-X bike can be had on any Thursday BMX bike. The brake hose runs through a steel tube in the frame top tube, surfaces to get around the seatpost, then dives into another steel tube inside the seatstay. Then it pops back out just ahead of the brake caliper.
The internal hose appears from nowhere!
The Profile hub with disk brake rotor mounted. For pricing and availability, go here.
No longer available is the Stealth from True Precision in SoCal. Another pricey unit. Call them up and beg - maybe they'll kick out a unit for you!
Thursday plans to run a 24 and a 26 with the new brake setup this coming season. Likely places to catch up to the man are ABA Salt Lake City, Mile-Hi, Fall Nationals in Albuquerque, maybe even the Grands! .. or any of the State Championship series races in Idaho. If you see him, ask for a demo ride!
