Retrofit solutions for disk brakes
(and information on the Formula disk brake
on my hardtail off-road tandem):
A tandem ridden in the mountains needs a non-rim brake to prevent an overheating of the rims which can and often does lead to tire failure. Most tandemists use an Arai drum brake threaded onto the rear hub for this purpose. The problem with this approach is that one now needs to control three brakes. To do this, one can either give the stoker one of the three brake levers, run two brakes off of one lever, or use a ratcheting shift lever (bar-end or Suntour Command lever for drop bars, thumb shifter for flat bars) to control the drum. I like none of these approaches very much, especially in competitive off-road riding, so I decided to add a disk brake to my tandem. I chose an open-system Formula hydraulic disk. The disk mounts to the hub via a home-made thread-on piece. The brake caliper is mounted to the frame using an aluminum plate that I designed. The plate uses the existing pac-man mount below the chainstay intended for the drum. In the rear, it rests between two spacers on the axle. The plate does not interfere with wheel removal, it can simply stay in place. I used a braided 'Steelrod' hydraulics line, but mainly because it was the only one I could get in the required length. The pics shown here were taken when I still only had the short original tubing (forcing me to mount the lever to the stoker's bar for the first trial runs).

Download the pic for the original drawing of the frame adapter. Do note that a considerable amount of manual work was required to get it all to fit right. Also not that this adapter is not I.S. compatible. I am using a 1999 Formula with a non-standard rotor size. This drawing is only provided to give you an idea of how such an adapter could look.

I mounted my Formula a day before the 1999 Kirchzarten Mountain Bike Marathon. It took about a third of the race for the brake to break in and give good braking power. It did provide good braking for the rest of the ride.

I have done about 500km with this setup now, and I still love it for most rides! With the 185mm disk, it is a bit weaker than with a well-set up rim brake, but that's okay for a rear brake. The 203mm disk, which Formula only supplies to Santana, should be better. Do not try a disk smaller than 185mm on a tandem!

We did have total loss of brake power during a long-distance off-road event, however. I have refilled the system and we have not had the brake fail since. That event did cause me to lose some confidence in the brake for extremely long downhills, though. If I were to get a new disk brake for the bike, though, it would either be a Hope 04 DH or Magura Gustav M.

May 2000 update: I rode the bike again in the 2000 "Warsteiner" Marathon in Riva/Italy, and it did hold up to some extreme descents. The brake provided good braking and excellent modulation thoughout the entire event. We did lose some fluid at the lever, though not enough to cause the brake to stop doing its job. It shows that the brake was certainly at its limit, however. I have since upgraded the brake fluid to DOT 5.1 and hope to see improved results.

Januar 2001 update: Several test runs in the Black Forest convinced me that even with DOT 5.1 fluid (of which Formula said that itwould greatly improve my brake's stamina) the Formula is not really up to the task of slowing down a tandem. I may give Motul's Racing 600 brake fluid a try, but I may also change to Magura Gustav Ms front and rear (also had a heat-induced front blowout ion one ride - scary!).

March 2001 update: I give up! My new full-suspension tandem will be outfitted with front and rear Magura Gustav M disks.

A few manufacturers offer a different type of disk adapter which simply bolts on to any existing frame, but doesn't look nearly as nice as my design. The left pic shows the Point Racing adapter, while the right pic is the Hanebrink version. The pictures of the far right show elegant homemade adapters made by Marko Ursin from Finland (see here for Magura's ad with a pic of Marco) and Martin Dierker from Germany. See here for more detailed reports.

For more info on disk brakes and tandems see the following pages: