Cyclocross disc brakes: it gets serious from here on out10
by Mark V on Jun 19, 2010 at 11:19 PM
p> It’s official: the UCI has declared that disc brakes will be legal for all cyclocross competition for the 2010-2011 season. The rumour circulating the interwebs is that Shimano made a push to convince the UCI to make the rule amendment.
Among the advantages of disc brakes is that rims can be made lighter because they wouldn’t need to act as braking surfaces. Riders will be able to brake more effectively in all conditions particularly mud, and there wouldn’t be brake pads next to the rim to pack on mud. However, forks would need to be beefier.
All this has been mentioned for years, but now it seems that with the UCI’s blessing, we are perhaps now on the eve of the next big revolution in bicycle equipment. Cyclocross is the doorway through which disc brake systems integrated into dropbar shift/brake reach the consumer as well as the natural path for discs to reach UCI acceptance to road racing.
That said, there’s a number of design issues which I’m gonna love seeing Shimano and SRAM overcome….
The first issue is whether the brakes will be mechanical (cable-actuated) or hydraulic. Cable-actuated brakes for dropbar levers are already available and have been for years. You can already buy the BB-7 road disc from Avid (a SRAM sub-brand) and also Shimano’s BR-505. But I hardly expect the top pros to convert to those brakes en mass. Those guys are going thru a lot of trouble to get bikes superlight; I’d be shocked if they’d be that willing to readily accept the 1+lbs penalty that currently available disc brake systems would bring. Of course, the current cable discs on the market were not engineered for top-level competition, but in the very competitive mtb market hydraulic is the choice for weight and performance.
Besides, if the rumours about Shimano championing discs to the UCI are true, I would have to assume that they already have prototypes for the next generation disc brakes. According to the story, Shimano had equipped a bike to show the UCI a few months ago. And there’s one thing about Shimano: when they decide to do something they go all-in. Maybe they have developed a new light weight cable disc, but I wouldn’t be surprised if they had a hydraulic brake lever with integrated shifter. After all, STI (Shimano’s term for integrated shifter) actually stands for Shimano Total Integration.
From a more cynical standpoint, if Shimano makes an integrated shifter/hydraulic lever then the consumer MUST buy the entire system: derailleurs, levers, brakes, probably rotors, and possibly hubs/wheels. Cyclocross from its inception has involved parts kit cobbled together from disparate sources; Shimano could potentially create the first true cyclocross gruppo.
The next issue is the design of the lever, assuming that the brake calipers will be hydraulic: where to put the master cylinder for the system. For those not really savvy with the inner workings of a hydraulic system, the master cylinder is a fluid filled tube with a piston. Your hand movement at the lever pushes the piston in, forcing fluid out of the piston and into the caliper at the other end of the system. The caliper has one or more cylinder/pistons. Relative to the master cylinder, the cylinders of the caliper a short length and wide diameter so that the calipers piston (s) move a shorter distance than the master cylinder’s piston but with a lot more force. And the caliper’s piston(s) move the brake pads against the disc rotor.
On a typical mtb lever, the master cylinder is part of the lever body and the lever blade directly drives the master’s piston. This is the most straight forward way to do things. There have been examples where the master cylinder has either been built into the caliper or at some intermediate point between the lever and caliper, in both cases a cable connects the master to the lever. Historically, these systems were used as a way to combine hydraulic systems with existing cable-actuating levers, created by companies that didn’t manufacture shifting systems. In most cases, these systems have fallen by the wayside as better, pure hydraulic systems have reached the market.
So that leaves us with trying to cram a master cylinder into a Shimano STI or SRAM DoubleTap lever and make the master cylinder serviceable. There’s not a lot of excess space in the current lever designs. Magura used to make a hydraulic dropbar lever (for hydraulic rim brakes), but that didn’t have shifter functions. I’ve thought about this off and on, and it seems to me that the previous generation of Shimano STI, as exemplified by Dura Ace 7800, was the best starting point for a shifter/hydraulic-brake lever because the shifting functions were all in the front of the lever, in the lever blades themselves. The levers bodies were mainly empty space. Whether Shimano would take the aesthetic leap backwards to exposed shifter cable routing is another question.
Frankly, I never had much issue with the exposed cable routing of the old STIs. All the latest integrated road levers…Campag, Shimano, and SRAM…are a f*ing bitch to replace shifter cables and housing on now. It’s definitely a case of aesthetics over functionality. And even if SRAM and Shimano don’t intend on consumers or even shop mechanics to be able to service the shifter mechanism, it unlikely that they expect to be able to sell non-serviceable hydraulics. A lot of people keep telling me that the engineers will just make everything small enough to fit as if these things were like other consumer goods. But this isn’t like making a new, smaller iPod…the mechanisms and volumes are largely dictated by the forces that need to be applied. Take a look at side-pull caliper brakes on road bikes: if anything they have gotten bulkier today than in the past, even if careful shaping and materials selection has kept the weight down.
Of course, the ultimate solution might be to have an electronic Dura Ace (Di2) lever incorporating a hydraulic brake system. After all, if the shifting functions can be electronic and thus minuscule, then the braking structures can move into the vacated space. The shifting buttons and wiring are so light and discrete that it would be a relative cinch to make the hydraulics fit. But considering how expensive a regular Di2 shifting system is now, the cost of such a hydraulic version would just be mind-blowing.
So here are my predictions for what happens next:
1) Sven Nijs will be running prototype Shimano disc brakes on some of his bikes.
2) Most of the top amateur and professional cx racers will be racing with cantilevers however, because
3) it’ll be another year at least before the light weight brakes are widely available.
4) there’ll be a 2nd tier cost/weight/performance level product that will cater to the needs of commuters, touring riders, and other non-elite cyclists. It will most likely be cable-actuated.