A few weeks from now I expect that TRP will officially debut their Spyre dual-piston mechanical disc brake for road bikes at either the Taipei Bike Show or Sea Otter in California. The Spyre seemingly has the potential of stealing the road disc championship from the venerable BB7 from Avid (SRAM). The TRP product differs from almost every other cable-actuated disc because both pads move rather than having one pad push the rotor into the opposing (static) pad. This is significant because it increases rotor clearance, so that effects of rotor warp and pad wear are minimized. It doesn’t hurt that early pre-production samples are lighter than the BB7 as well.
Personally, I’m a little keener on the other road offering from TRP, what is being called “HY/RD”. It is a hybrid cable-hydraulic caliper with dual pistons. A standard brake cable enters the caliper and pulls a small lever arm that actuates the master cylinder. Contrast this to TRP’s current hybrid design, the Parabox, which puts the masters cylinders for both front and rear caliper in a box that attaches to the steerer tube, sitting below the stem. The HY/RD’s advantages over the Parabox include easier installation (presumably no bleeding is necessary and there is no hydraulic hose to speak of) and no issues with stack height interfering with handlebar height. On the other hand, the HY/RD is a rather bulky caliper, and I am somewhat cautious of how well it can deal with heat build up.
The main reason I’m interested in the HY/RD is that I can use my current levers. Without a doubt, full hydraulic brakes with integrated shift levers are on the way from SRAM and Shimano, but they’re bound to be a heavy investment for most consumers. And why should I have to pay for what might very well end up being a beta-test of product that has yet to fully mature? Full systems integration is certainly a double-edged sword if any aspect is problematic. And since cyclocross use is my primary interest and breaking levers during racing is a talent I’ve already demonstrated, I’m not too keen to put such cutting edge technology on the front of my bike just to meet blunt force trauma. If I go with the HY/RD, maybe I’ll get all the power and the self-adjusting pad feature of hydraulics with the penalty of a little cable drag. And that can be minimized with high-quality, sealed brake cable/housing kit.
Still, I’ll hold off recommending the HY/RD system for road riders, particularly touring cyclists, until I can get my hands on a set. Heat management is going to be the biggest design issue for hydraulic road discs, and the heavier loads imposed by touring bikes puts them more at risk. I get the feeling that many riders are going to be installing hydraulic road discs and using them without proper respect for their design parameters and operational limits. Cyclocross is actually more forgiving in the sense that the speeds are lower and there are no long descents.
The idea of combining cable-actuation and a hydraulic master cylinder into a cable is not new. AMP Research (and I think maybe Hayes too?) marketed one in the early 1990s that was a decent performer. Of course, perhaps twenty years from now the HY/RD will another piece of forgotten trivia, a stopgap technology quickly discarded once full hydraulic system came of age.
AMP Research brake