After about a year of teasing (and plenty more years testing), SRAM has finally unveiled their hydraulic disc and rim brakes for road bikes.
Called SRAM Hydro R (as in Hydraulics for Road), they join the lineup as top-level options for the new SRAM Red 22 and Force 22 11-speed groups. Mechanical rim and disc brakes will still be available as well as all-new very similar 10-speed S-700 series hydraulic brakes will be available, too. The idea was to make hydraulic brakes available to all current SRAM road groups, whether they’ve been on your bike for five months or five years, and give riders more options. Heck, they’re even offering standard and “moto” (left hand brakes the rear wheel) setups.
Options are good, but the real reason for moving to hydraulic brakes is to improve power, control and modulation in all conditions. The Hydro R rim brakes produce more braking force with less hand effort, in and of itself a great feature. It’s also a closed system, so it should feel as good in a year as it does on day one. And the disc brakes are even more powerful…
THE DEVELOPMENT STORY
About three years ago, they made an external master cylinder placed inside a stem, thinking it a good idea to make it compatible with any standard mechanical lever. But, they couldn’t fit it in anything less than a 110mm stem, and as SRAM’s road groups gained traction, they decided it was better to create a completely closed system.
This was before the UCI allowed disc brakes on cyclocross bikes, so they were looking at rim brakes. They wanted something that could quickly retrofit to any single-bolt brake mount (i.e. virtually all road bikes) that would offer better power and modulation while also eliminating cable drag associated with ever more complex internal routing frame designs. Then, of course, disc brakes became legal, so they started working on those, too.
What they found was quite interesting. Despite the rim essentially being a much larger diameter rotor than, say, a 160mm rotor, the disc brakes turned out to be substantially stronger. The brake force to lever force ratio came out with discs clearly on top:
From there, they strapped on weight vests to get up to the 250lb system weight and started bombing down hill. Hydraulic brakes product manager Paul Kantor said they expected to boil the fluid during long descents while dragging the brakes, but that didn’t happen. Nor did it overheat during very rapid deceleration, but those tests did cause quick pad deterioration. So they switched from drilled alloy-backed pads to solid steel, and that held up better. The alloy backed pads with holes in the back were getting odd temperature spikes. They also switched to a different organic compound, a variant of what’s used on the mountain bikes. Metallic and semi metallic created too much heat.
With heat testing as a non-issue, and more power available to the rider, are there any other benefits to going to disc? Possibly. They found that sustained braking for five minutes generated about 550 watts of energy on a rim brake with carbon fiber rim, which made enough heat to blow out a tire. However, on discs, they could drag for 12 minutes, producing about 800 watts, with no brake failure and, obviously, no rim/tire failure.

With all that said, these testing conditions are far beyond the “normal operating range” of typical riders, even those riding in the Alps. They did test disc brakes with more initial bite and a higher overall brake force power. The only benefit was improving the “parking lot experience” with more dramatic stopping power, but modulation and control suffered. And, as many readers have commented, it’s already pretty easy to lock up a road bike’s tires, so massively increased power wasn’t the goal. More control and improved safety was, and they say they’ve nailed it.
And, for the rim brakes, more power doesn’t mean you’re more likely to overheat your rims. It does mean you’ll be able to brake harder and later, but for less time. You’re creating the same amount of heat energy during braking to accomplish a set amount of deceleration. And, ultimately, tire traction is going to be the real-world limiting factor.
- DOT5 has a boiling temp of 380ºC, but even when rotor temps hit that or higher, it’s not immediately transferred to the fluid. In the unlikely event it did boil, it would cool rapidly (a few seconds) and should be fine.
- Ambient temperature had no noticeable effect on the system.
- For rim brakes, heat transfer’s even less of an issue. The rim brake pads dissipate heat quickly, so very little of it’s transferred to the caliper arms, and even less is transferred to the “toilet tank”, as they affectionally call it, where the fluid is.
DESIGN DETAILS & SPECS
