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Take a quick spin on a mountain bike equipped with modern hydraulic disc brakes and you’ll immediately realize that road cyclists have gotten a raw deal. Although cable-actuated rim brakes have gotten really good, even the very best feel genuinely archaic in comparison with a hydraulic disc setup. After a long wait, road bikes are about to catch up.
SRAM has created two types of hydraulic brake specifically for road. We triathletes, however, will have to wait before racing with SRAM’s hydraulic stoppers—they don’t yet have a version compatible with aero brake levers.
Anatomy of a hydraulic brake
Hydraulic brakes push fluid to actuate the caliper instead of pulling a cable. Pulling the brake lever drives a plunger into a line filled with fluid that connects to the caliper. Moving that fluid through the lever moves the brake pads. The details vary between each design, but swapping a cable for this fluid-filled connection is the fundamental difference between a traditional road brake and hydraulics.
What’s the point of a hydraulic brake?
The reason to switch to hydraulic brakes (especially hydraulic disc brakes) is pretty simple—they work better than cable-powered brakes in every possible way. Hydraulics allow the rider to apply greater and precise braking force to the wheel using less hand force. Braking quality doesn’t degrade in the months after they are initially set up because the line that connects the lever and caliper is sealed. Road gunk accumulates in cable housing, which prevents the cable from sliding smoothly.
SRAM has two different types of hydraulic stoppers. The first is a hydraulic rim brake SRAM has named Hyrdo R Rim, or HRR. While the mechanism that actuates the brake has changed, this version has a rim caliper that bolts to any road frame with standard brake mounts.
The second version is a hydraulic disc brake named HRD. Instead of pressing against the rim, this brake squeezes a disc mounted to the hub.
Both brakes are actuated using the same shifter, which contains the master cylinder that actuates the brake as well as SRAM’s typical Double Tap shift internals. Sadly—almost tragically—they do not have a brake lever that is compatible with an aero bike. These brakes will be limited to road bikes for now.
What about us?
As is often the case, triathletes will have to wait until SRAM releases the next batch of technology before we get to equip aero bikes with these phenomenal brakes. When asked if there is a tri-specific version coming soon, SRAM’s hydraulics category manager Paul Kantor responded by saying “we are always working on something new.” Basically, Sram is planning to makes a tri-specific version but it isn’t ready yet. Margura’s RT 8TT and RT 6TT hydraulically driven rim brakes are still the only aero-equipped hydro brakes, for now.
Initial ride impressions
Hydraulic Road Disc
These brakes are simultaneously the most powerful and precise stoppers I’ve ever experienced on a road bike.
Jam hard on the brakes and they can stop a bike as quickly as the tires will allow. (Expect these brakes to advance the trend to broader tires.)
They scrub a little speed without grabbing the rim and jerking the bike forward. Feather the lever to find the perfect amount of stopping power the HRD brakes predictably increase and decrease the stopping power.
In short, they feel incredible. I may never buy a road frame without disc mounts again. These brakes (and the promise they show) are that good.
Hydraulic Road Rim
Switching from a cable-driven SRAM Red brake to the hydraulically powered rim stopper gives the feeling that your hands have gotten exponentially stronger. Maximizing the stopping power of each rim-and-pad combination is easy when using these brakes.
When the brake first contacts the rim to scrub a little speed, it doesn’t grab or catch. The stopping force increases gradually and predictably. The sensation while braking lightly is very familiar.
Ask the brakes from a little more stopping power and they ratchet up the force with a gentle squeeze of the lever. Instead of clamping down with your fingers, a gentle tug is all it takes to rapidly slow the bike. There is no need to switch hand position from the hoods to the drops to get full stopping power out of the bike.
The HRR brakes are so strong that learning the right amount of forces takes a little acclimation. I occasionally reverted to old habits and squeezed too hard, causing the rear brake pads to skid against the rims. After rapidly slowing for tight corners on a couple technical descents, I quickly learned to depend on my front brake even more than normal. The HRR brake caliper is so powerful that I could use even less rear brake than with a normal cable-driven caliper.
One of the biggest difference between a triathlon bike and a time trial bike is that a tri bike is the athlete’s primary bike, the one used most often, while a TT bike is a rarely used tool for select road racers. Because a typical triathlete logs so many more hours in the aero position than the average cyclist, braking performance is really important. But tri bike brakes also have to be aerodynamic. While some sources have said that disc brakes do not create a significant aero penalty, conclusive evidence has yet to be made public. In order for the HRD brakes to be genuinely applicable on tri bikes (when SRAM eventually does make an aero brake lever), they must be equal or almost equal in the wind tunnel to rim brakes.
The HRR (rim) brakes, however, seem like a nearly ideal solution to aero braking. Not only are they incredibly strong and functional, but small as well. The caliper is substantially narrower than a typical Sram or Shimano brake and should fit in front of many forks without jutting out to the sides.
Also, passing a hydraulic line through the twisted routing pattern required by some aerobars and frames does not denigrate stopping performance. A looping path that would turn a cable brake into a sticky, gummy mess wouldn’t be a problem for SRAM’s HRR calipers. For these two reasons, the hydraulic rim brake seems likely to be the most applicable for aero bikes.
What this means for the future
Allow me to speculate. Just as carbon frames have pushed aluminum frames into obsolescence at the mid to high price ranges and electronic drivetrains are poised to do the same for shift components, I fully expect hydraulic braking to become the standard for road and tri bikes in the near future. Other than the very high price, which hopefully should fall rapidly, there is no functional reason cable brakes should beat hydraulics in the long run. The move happened with mountain bikes, and it will happen again with road bikes.
Cable brakes will always have a place on mid to entry-level bikes, but hydraulic stoppers will become the new standard at the stratospheric price points.
Why so late?
Adapting disc brake technology for road bikes took many years, and heat management was the biggest hold-up. Continuously applying moderate brake force puts more heat into the brake pads and surface than periodically braking very hard. Ride a disc brake for too long and the hydraulic fluid, in this case DOT fluid, gets hotter and hotter before eventually boiling. When that happens, the brake looses the power until the fluid cools. SRAM’s hydraulics guru Paul Kantor says it takes roughly 30 seconds for boiled DOT fluid to return to normal functioning temperature.
So, a rider who descends a long mountain pass without letting go of the brakes runs a greater risk of boiling their brake fluid and losing stopping power than does a person who lets their speed build on that same descent then braking hard before each corner.
Since road riders often build more momentum (much less rolling resistance) over longer descents than mountain bikers typically ride, the brake boiling issue was a bigger problem for adapting disc brakes for the road.
Through testing in the European high mountains and in the lab, Kantor found that the HRD brakes can apply 800 watts of stopping power for 12 minutes before boiling while the tire on a rim brakes reached unsafe temperatures after creating 550 watts of stopping power for just five minutes.
SRAM is offering two levels of both the HRR rim brakes and HRD disc brakes. The top level Red 22 HRD shift/brake levers with all the necessary parts cost $1,403 for a set. Drop down a step to S-700 levers and the price becomes $1,080. Weight, materials and appearance are the only difference between the two systems. Also, those wheels you’ve collected over the years won’t do you any good. Only wheels build with disc-specific hubs are compatible.
A Red 22 HRR setup will run $1,196 and the S-700 version will go for $800 and any road wheel is compatible.