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.
Kantor says there are two break in periods with the disc brakes. The first is the usual pad bed in procedure. Then, after the first few sustained braking efforts (say, dragging down them down a hill for a few minutes), the pads will heat up and change a bit, and then power should increase slightly.
A few other technical points they mentioned:
- 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
The head of the unit is the same for both disc and rim brakes. It has a new master cylinder design, quite different from the Taperbore levers on Avid’s mountain bike brakes.
Like their Avid brakes, it uses DOT5.1 fluid, and it’ll use the same bleed kit, and Avid’s Pro Bleed Kit is arguably the best one out there.
The Hyrdo R disc calipers use 19mm front / 18mm rear pistons. The caliper and piston ratio are different than what you’ll find on mountain bike systems, it’s not just a mountain bike system ported over for the road. The smaller caliper on the rear helps reduce the likelihood that it’ll lock up.
We mentioned that the new Connectamajig will be offered for use with this, and it’s aimed at the OEM manufacturers to ease assembly line efforts. SRAM’s product managers were careful to point out that it’s not really designed to be a quick disconnect for travel frames, it’s primarily to make installation easier.
They’ll have inline and caliper mount versions, and they’ll have different seals and rubber parts inside than what’s available for the Reverb since one uses DOT5 and the other uses suspension fluid. For frames using the caliper mounted version will have the Connectamajig incorporated into the Banjo, which is their preferred method for using it, but it’ll require a slightly larger hole in the frames (about 7.5mm diameter) to feed the line through. The goal is to reduce or eliminate a factory’s need to bleed the system during the installation process, something that could lead to inconsistencies in performance by the time the bikes hit your local shop’s floow.
One common question leading up to disc brakes on road bikes is how a tiny rotor can compare to the massive “rotor” that is the wheel’s rim. I asked Kantor how they got more power from a much smaller “rotor” with the disc brakes, and this was his reply:
“Disc brake friction materials are much better for braking but no good to make a rim out of. There are a lot of things that go into it, but this is the biggest factor.”
I also asked how they compared to BB7 mechanical disc calipers:
“Yes (we benchmarked these against the BB7’s. They’re) a little less grabby off the top because the BB7’s use sintered pads. Power is comparable. And the pad wear rate is similar to our other organic materials.”
The bottom of the pads are angled to make for quicker, easier wheel changes…particularly important if these are ever to be adopted by the pro peloton. Be nice if this transferred to their mountain bike brakes, too!
The Hydro-R Rim calipers are an incredibly simple system. Fluid comes in, makes a U-turn and pushes a small piston up. Both arms rotate on a single pivot…
…and the piston’s movement is minimal. At left, the brake is open, and at right, it’s closed to stop the wheel from turning. Note the wide part of the piston sticking up just a couple millimeters more. Here’s a close up:
That’s it. That tiny bit of movement is more than enough to lock up the wheels.
But you have to move the levers this much to do so, and that’s the key to these brakes’ incredible modulation. Unless you over react or just grab a fist full of brake, you have very fine control over how much power you’re putting into the brakes. And because it’s fully closed, and there’s no cable friction, it’s unbelievably smooth.
They’re compatible with rim widths up to 28.4mm, and the contact adjust knob and quick release knob on the top of the caliper are super easy to use and provide a good range of adjustment.
The HSX and other rotors will be sold separately, so you buy only the size you want/need. They’re requiring OEM spec of 160mm for pavement, but offering 140mm for cyclocross. The 160mm rotors are designed around a 250 rider/bike combined max weight. Larger riders should opt for even bigger rotors (and make sure their frame and fork can handle 180mm+ rotors!). Sorry tandems, this isn’t for you yet.
The S-Series Hydro-R brakes are your 10-speed options. SRAM will continue to support 10-speed systems, and the current 10-speed Red and Force systems will stay in the line. The S-700 Hydro-R levers and brakes allow anyone to add hydraulic brakes to their current 10-speed SRAM group. The front shifter is YAW compatible, meaning it’s designed for 2012 Red, but cable pull is sufficient for older, non YAW 10-speed systems. It just won’t have the two position trim for the big ring.
The main differences in the RED and S-700 brakes are titanium versus stainless steel hardware and carbon versus alloy shifter/brake levers. Functionally, they’re identical.
For TT and Triathlon bikes, they’re “always working on new stuff”, which should be interpreted as hydraulic levers and possibly even dual bolt mount brakes are in the pipeline.
RANDOM QUESTIONS & AERO COMPARISON
Did the road discs produce higher overall heat than MTB systems?
“No, haven’t seen peak temps go any higher as what we consistently see on mountain bikes.”
What’s dissipating the heat in such a minimal package?
“The sustained temperatures are typically lower (on the road), and the caliper has a more open construction with more air flow through it.”
Are current road forks and skewers up to snuff?
“Yes, they’re not all that different from mountain bike QR skewers.”
Do you see thru axles as improving the road bike with regards to brake performance?
“We’ve done some testing, but we couldn’t tell an appreciable difference.”
SRAM made a big deal about aerodynamics with the 2012 RED launch, so it was a little odd they didn’t mention the minimized frontal profile of the hydro calipers. Side to side, the Hydro-R calipers stay within the frame’s width much more, which leads us to think they’ll contribute to an overall more aero bike/parts package. Plus, it just looks better. For TT/Triathlon bikes, that’s an obvious boon, and the slippery feel at the lever will remain regardless of the convoluted hidden cable routing some aero bikes employ.
Hydro-R Rim Brakes: There’s a tiny bit of free stroke at the lever, about 4mm at the bottom of the lever, before the calipers start to move, which isn’t noticeable while riding. The amount of lever pull is greater than the movement of the caliper’s piston, which gives you a ton of fine modulation. The feel is head and shoulders above cable systems. That said, it’s still braking on a carbon rim. As good as Zipp’s rims and pads are, I would have like to test them on alloy rims, too. Even SRAM’s test results (see chart up above) show higher braking power on alloy rims.
Hydro-R Disc Brakes: Given my history with disc brakes and steep roads, this was one item I was very, very keen to test. It would either seal the deal that road bikes and disc brakes don’t mix, or restore my faith in systems engineering to make it work. I’m very happy to say it’s leaning towards the latter. We tested them on some long, steep and wicked fast descents (I’ll add Garmin map data as soon as I can), and the disc brakes were far more confidence inspiring than the rim brakes. I felt like I had more control and could stop quicker. On one particularly long, straight section, I got up to 43mph then grabbed as much brake as I was comfortable with and slowed a crawl. I repeated this quickly three more times in rapid succession, sprinting then emergency stopping, and there was no fade. I’d liked to have been shuttled to the top again and let them drag all the way down then see what was left at the bottom, but that’ll have to come when we get our own set in for long term testing.
Was it perfect? No. There was still a bit of the warbley sound that Avid and other brand brakes sometimes make, and at the end of one ride the rotor was lightly-but-consistenty rubbing the outside brake pad on the front wheel. These sorts of things might delay uptake among pure roadies, and they should find ways to remedy this as it’s more noticeable on skinny tires. Kantor said the pad retraction on the Hydro-R calipers is slightly greater than on their mountain bike calipers, but it might need to grow a hair more. Or, the set up could just take a bit of tweaking…these were some of the first ever rides on the brakes after all. For now, I’m optimistic. First impressions are good, and the general consensus among the other journalists seemed pretty positive. For me, the most telling statement is that, despite past experiences, I’m really looking forward to getting these on my own bike for long term testing.
THEY’RE ON THEIR WAY
So, are disc brakes the wave of the future? Without disclosing any names, Kantor says OEM buyers for “major bike brands” have been more interested in the disc brake system for both road and cyclocross. And they’ve been working with frame manufacturers to develop bike/component systems that take full advantage of the new parts. And speaking of the future, they do have demand for under-the-bottom-bracket mounted rear brakes, common on TT/Tri bikes, which could mean a dual mount rim caliper.
Both the RED and S-700 hydraulic brakes will be available this July. Check the RED 22/Force 22 drivetrain post for a complete breakdown of pricing, availability and actual/claimed weights.