Tandem Cycling - How to set up rear disc coaster brake

My current 26 inch road tandem has rim brakes. I have found a good rear wheel with a Phil Wood disc hub. I'd like to know how to keep my rear rim brake but add the disc as a coaster (or whatever you call a brake that slow your downhill speed). What lever could I use to apply the disc brake? I think I've heard of people using bar end shifters. Would that work?

People definitely use bar end shifters with drum brakes as a drag brake.

However, its generally not recommended to use a disc brake as a drag brake.

Why not?

FWIW: The short-lived Phil Wood disc brake of the late 70's / early 80's was problematic at best, and the source of legal woes at worst. In fact, I'm pretty sure it was that product that precipitated Phil's retirement / sale of his business to Peter Enright back in the early 90's.

Might want to do some checking before hitching your wagon to that particular brake if your safety will depend upon it and/or if you will need any service or support.

Why not?

Because they are not designed to dissipate heat like a drum brake. They are typically a great primary brake, (excepting the Phil that TG noted), but not one to "set and forget" on a fast five mile downhill to scrub off speed. You'll potentially melt the pads and warp the rotor.

Oh, and what you're looking for we typically call a "drag" brake.

Why not?

While disc brakes typically have far more heat capacity than rim brakes, they do not have as much heat capacity as the tried and true Arai drum brake that has become the default 'drag brake' for tandems.

The extreme heat generated by prolonged use of a disc on a road tandem will:
1. Boil hydraulic fluid, which is why only mechanical discs are even suggested for use on road tandems.
2. Heat calipers to the point where non-metallic parts used as part of the calper or brake cable housing can begin to break down or melt.
3. Heat rotors and brake pads to the point where brake fade makes the brake ineffective
4. Heat rotors to the point where they will warp and may no longer run true even after cooling

Therefore, while discs -- just like rim brakes -- can be 'ridden' for short periods of time on a long descent, there are limitations on just how much heat they can safely handle before brake performance deteriorates. It is not as big of an issue when a disc is used as a supplemental brake to a second, primary rim brake; however, the problems associated with overheating a disc remain valid.

Conversely, a true drum brake is used only as a supplemental brake to a rim brake and the very large braking surfaces, the mass of the housing (think heat sink) and larger brake pads made them ideally suited fo drag brake applications.

If you're concerned about downhill braking then the idea of a secondary brake may make sense, but get a contemporary design disc. On the other hand there are a number of posters riding in quite hilly country using only (modern) v-brakes. Technique has a lot to do with brake performance. Normally, unless the terrain is very steep, coasting between curves will take advantage of aero drag and keep your energy in check. A hill only represents a certain energy input into the system; the faster your average speed the less total heat load your brakes and rims need to deal with. But , keep it safe!

Thanks, lots of great info.

Okay, what if I installed a modern disc brake setup and kept my rim brake, where would I install the disc brake lever? On the rear handlebar, work in tandem with the stoker on downhill braking?

Okay, what if I installed a modern disc brake setup and kept my rim brake, where would I install the disc brake lever? On the rear handlebar, work in tandem with the stoker on downhill braking?

Unless your frame was designed with disc brakes in mind, I don`t think it`s possible for you to mount the calipers. If you do figure out a way to do that, yes- drag brake levers are often located on the stoker`s bar. I think the "normal" braking method is just to have the stoker apply the brake and leave it applied until you don`t need it any more while the captain modulates the primary brakes as needed. This is just my impression though, because we don`t do hills that require our drag brake and mostly just use it for a parking brake. Works great for that!

Frame is already set up with cantilevers and has appropriate design to mount a rear disc. I'll probably slowly gather the needed parts and eventually add the rear disc brake and just put the braker lever on the stoker handlebar. Really don't have that many significant hills around here. But I do love to tinker.