Hydraulics for Roadies

The Magura RT8TT Hoverboards. I can’t speak for every kid of the 80′s, but if there’s one future tech I was promised that science has truly failed me on, it’s the hoverboard. My bike sufficed—I could jump it off things and catch a little air while I waited for the hoverboard that my best friend’s older brother told me was real, and just being suppressed by corporations hell bent on keeping kids from having fun. Our days of hoverboard mischief were just around the corner.

The years went by, I kept riding my bike, but I still have no hoverboard. Corporations: If the hoverboard is real, please don’t release it. I have kids now, I understand.

Over the years, I’ve followed a number of the technological advances that were supposed to be just around the corner for bikes that excited me almost as much. One of the biggies was electronic shifting. Electronic shifting, from Mavic, really never felt like it was going to take off. Finicky, prone to malfunctions, expensive—when it worked, it was great. When it didn’t, it was a mess. I figured electronic shifting would never hit the mainstream.

Then Shimano Di2 came out. Campagnolo EPS, 10 plus years in the making, was available. With the release of Ultegra Di2, its safe to say electronic shifting has left the realm of just around the corner, and hit mainstream. Sometimes, the advances we think will never come really do become reality.

The other big item I’ve been waiting for is disc brakes on road bikes. You’d think, being a well understood technology, we’d have them by now. With them now legal for cyclocross, it may just be a matter of time—mechanical discs are already making inroads, and while solutions for using hydraulics are a little hokey now, we’ll probably see something available sooner or later. If I keep saying any day now, sooner or later I’ll be right.

One thing I never saw coming was hydraulic rim brakes. I’m trying to decide if they are a technological advance, or just a Mektronic on the path to disc brake Di2. Or EPS—no allegiances here.

Magura’s announcement as a sponsor for Garmin-Barracuda started the rumors flying. Magura confirmed their re-entry in to the road hydraulic market with a hydraulic rim brake, the RT8, initially available as a time-trial only version (RT8TT) mated to the Cervélo P5 time trial frame. In a few months, we’re told, it’ll be available without the Cervélo for both road and TT use. How that’ll work in a world where most people use integrated brake/shift levers remains to be seen. Details are just around the corner, I’m sure.

Before we discuss the merits of Magura’s offering, it’s worth understanding a little about hydraulic brakes. For the dirt-phobic, this may be the closest you’ve come to them, and while it’s unlikely you’ll be seeing Magura’s offering on your group ride any time soon, you’ll probably hear discussion about it.

Hydraulics Primer

Hydraulics are pretty simple. A typical hydraulics system of any form is composed of a master cylinder, one or more slave cylinders, incompressible fluid like mineral oil or DOT, and hydraulic cable to connect them. Each cylinder contains a piston. Press the piston in the master cylinder in, the incompressible fluid moves out of the master and in to the slave, and the slave piston extends. Simple. Attach a brake lever to the master cylinder piston, and use the slave cylinder to actuate a brake pad, and you have the makings of a hydraulic brake.

There are two different kinds of hydraulic systems employed in bikes. Most hydraulic discs use the “open” system, where there’s a reservoir attached to the master cylinder to manage fluid fill levels in the system itself. Lots of braking can heat the fluid, causing it to expand and overfill the system. The same excess braking also contributes to pad wear, requiring more fluid in the system. The reservoir takes care of managing these levels.

In a closed system, there’s no reservoir. Just the master cylinder and slave cylinders, and a fixed volume of fluid.

Left by itself, pressing the master cylinder piston in moves the slave piston out, where it will happily stay. The “normal” solution involves using specially shaped gaskets, designed to “twist” along with the piston. When there’s nothing pushing on the master cylinder piston, both pistons will want to retract to their normal positions, giving the behavior you expect from brakes. Springs occasionally augment this sort of system.

The upsides to hydraulic brakes are numerous: low friction, one-finger braking. Great modulation and control. Consistent performance, devoid of changes due to cable stretch or wear. Most of all, they’re powerful—by tweaking the ratios of width and height between the cylinders, a mechanical advantage is achieved—1 pound of pressure at the master cylinder can exert many multiples with a proper design.

Magura’s Offering

The new RT8 brakes are a somewhat unorthodox brake design, if we confine ourselves to the notion of how disc hydraulic brakes work.

Magura has had a rim brake product line for years, targeted at the tandem market. These offerings, and it appears the new RT8 as well, utilize a “closed” hydraulics system. The master cylinder has no reservoir. This isn’t necessarily a problem, assuming environmental conditions stay pretty constant; heat generated by braking shouldn’t feed back in to the slave cylinder the way it might in a disc system, which directly actuates the pad. Pad wear is still something of an unanswered question in the RT8—this could very well be handled at the brake lever by adjusting the travel of the lever blade, or limiting the retraction of the piston.

RT8TT ActuationThe design of the caliper is somewhat of a throwback. The RT8 appears to utilize a cam-and-roller arrangement, where the slave cylinder pushes upward, moving an expanding profile cam, spreading the brake arms. Shades of the old WTB/Suntour roller cam brake or the Shimano AX? Perhaps. While the rendering of the RT8 shows a very triangular cam, changing profile and shape of the cam could allow for variable mechanical advantage—the design could allow for quick travel of the pad to the rim, with progressively increasing power following contact. Most of the downside to previous versions of this design involved setup: balancing the arms, maintaining pad positioning. Because the slave cylinder doesn’t directly engage the brake, there are springs on the RT8 to handle arm retraction. No word on whether these can or need to be adjusted for balance as you might in a normal roller cam.

So is it better?

Magura’s brake should offer stronger, quicker actuation with less effort than a typical brake. Depending on the terrain you ride, this may be a major advantage, or make no difference at all. For the cyclist who finds them selves climbing—and therefore descending—major heights, hand fatigue may be a serious problem. We haven’t seen a road brake lever yet from Magura, however. At the moment, unless you find yourself regularly descending on your time trial bike, this likely isn’t a major problem.

Power isn’t a major issue with modern road brakes. Enhanced modulation may allow a lighter touch ducking in to corners, and that could possibly lead to some speed advantages for the racers among us. Possibly. With situations where the brake selection itself is causing braking problems, then the RT8 might be a major advantage—with some time trial bikes utilizing low-travel lever blades connected to center pull and single pivot designs to smooth cable routing and reduce frontal profile, the uncompromising power of the RT8TT will be a welcome change.

Aerodynamics have been heavily touted for the RT8′s, with Cervélo playing a role in their design. It’s not an advantage afforded to it by being hydraulic, but may shave precious microseconds off times. We’ll have to wait for some testing to confirm this.

The Magura design may have one neat side effect. It hasn’t been discussed, but the closed hydraulic design of the RT8 may allow for multiple master cylinders. In an open system, where the master cylinders have reservoir, having a one master cylinder compress will cause the other’s reservoir to, over time, soak up the excess fluid in the system. In a closed system, so long as there’s no air in the system, there’s no place for the fluid to escape. Bleeding the system would bring new levels of pain to an at times trying process, but in theory, once its set up, it would work fine. I’m certainly curious to see if anyone is going to try mounting brakes on both their base and extension bars in a time trial. The ability to brake from the extensions and maintain an aero position could be an genuine advantage.

It’s less clear if the Magura brake will help with are the major issues big descenders have: rim sidewall damage, wearing out pads, and blowing out tires. Discs, by relocating the braking surface away from the tire, are the best hope we have for solving that issue once and for all. That and better technique.

The Cervélo P5Final thoughts

Under certain conditions I can see some potential upsides to Magura’s RT8 brake. Quicker actuation, more power and better modulation with less fatigue sounds like a win, if these are problems that plague you. Improved aerodynamics don’t do much for the recreational cyclist, but may be a win for those at the point where fractions of seconds matter. The multiple lever concept sounds cool, but whether anyone cares remains to be seen. We’re still left using the rim for a braking surface, though the enhanced modulation the Magura should offer might compensate a little for those with marginal descending technique.

It’s an interesting product, and one I’m curious to hear more about as details emerge. It’s unlikely, however, to satiate my desire for discs—or hoverboards.

Photos courtesy of Magura