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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. It's a little grabby until the pads break in, so
don't just mount it up and take it to the track! 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.
Juice
brakes … aren't they a little vulnerable for BMX use? But,
once you use them, you know you gotta have them. 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.
Something new! The
Kore disk break hub. This is an OK sealed bearing, cassette BMX hub
at an OK price. It is a special-order item, Thursday had a batch of
them coming in a container from ….. Taiwan! This has allowed me to put together a $200 disc brake wheelset. Still have a few left. Are they as nice as the Profiles? No, but they are OK for racing and will easily last you several seasons.
Thursday has
been running the 24 with the disk brake setup 8 seasons, and just
mounted up the 26 with a BB7 and Kore hub. They work flawlessly ….
never have to even think about your brakes ever again. They definitely helped the man get a couple state championships. Likely places
to catch up to the man and the bike in 2011 are ABA Salt Lake City,
Spring Nationals in Albuquerque, Northwest Nationals in February,
maybe Blackjack or one of the BC nationals! .. or any of the State
Championship series races in Idaho. If you see him, ask for a demo
ride!
