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by Matt Wikstrom
October 1, 2014
Photography by Matt Wikstrom
Shimano unveiled its first road hydraulic disc brake ensemble late last year with levers designed for Di2 transmissions. In this review CTech Editor Matt Wikstrom takes a look at the installation of the brakes and their mid-term performance.
There’s no point in debating the issue any longer — disc brakes have arrived for road cyclists. While the UCI has yet to endorse their use for road racing, many bike manufacturers have incorporated disc brakes into their road bike range for 2015.
And there’s no point in considering cable-activated disc brakes — they may be affordable, but they lack power. Hydraulic brakes are far superior in terms of power and modulation plus they require a much lighter touch.
At present, there are only a few manufacturers offering hydraulic road disc brakes: Formula, SRAM, and Shimano. Formula’s RR1 brakeset is designed to work with Di2 gear systems while all of SRAM’s hydraulic levers mate with mechanical derailleurs. Shimano’s first hydraulic lever, R785, is designed for Di2 transmissions, however a second lever for mechanical groupsets has been promised.
CyclingTips’ Andy van Bergen travelled to Hawaii last year for Shimano’s unveiling of the R785 hydraulic road brake levers. At the time, Andy was immediately impressed with the performance of the disc brakes on long descents and the light braking action, however his time on the bike was limited.
The R785 ensemble is now widely available and will feature on a multitude of 2015 road disc bikes. Shimano Australia recently gave me the opportunity to spend a lot more time with the R785 ensemble, including installation, to get a clear idea of its performance.
For this review, Shimano Australia supplied an R785 disc brake ensemble and an 11-speed Ultegra Di2 groupset with RX31 road disc wheels. They also sent along Pro Vibe 7s parts (bars, stem, post) and a Turnix saddle. Specialized Australia provided the frameset, a Roubaix Expert Disc, to hang all the parts on.
Installation of the disc brakes was straightforward. After several years of installing and bleeding Shimano MTB hydraulic disc brakes, all of the fittings for the R785 brakes were familiar. Indeed, the R785 disc calipers are derived from Shimano’s XT M785 calipers.
It is worth noting that Shimano now offers a second road disc caliper dubbed RS785. It differs from the R785 at the point of attachment for the brake line: R785 utilises a banjo fitting on the outside of the caliper; in contrast, the brake line attaches directly to the inside of the RS785 caliper.
In this instance, the RS785 calipers would have been a better match for the Roubaix frame since the brake line exits from the inner face of chainstay. As a consequence, the rear brake line had to make a severe bend to attach to the R785 caliper, which in turn, made filling the line difficult.
The R785 brakes were set up with 140mm Ice-Tech rotors front and rear with Ice-Tech brake pads. Shimano’s Ice Technology is designed to control heat generation during braking, thereby reducing the risk of brake fade. Ice-Tech rotors are constructed by sandwiching an aluminium core between stainless steel plates, such that the core serves to dissipate heat in the rotor, while cooling fins have been added to the top of the Ice-Tech brake pads.
There are two standards for disc brake rotors: one is a six-bolt arrangement to attach the rotor to the hub, and the other is Shimano’s Centre Lock, which mounts on a splined hub body like a cassette (indeed, the lockring requires the same tool as Shimano’s cassette lockrings). The choice between the two standards is dictated by the hubs, and in this instance, the RX31 wheelset accepted Centre Lock rotors.
Shimano describes the RX31 wheelset as an Ultegra-level product designed for road and cyclocross use. The rims have a 17mm bed and use 24 straight-pull spokes, front and rear. The wheels weighed 1,998g sans skewers and cassette. Fitting both rotors added another 204g. Shimano has unveiled a second road disc wheelset RX830 however there are no details on the weight of this wheelset or when it will be available.
The final build weighed 8.1kg sans pedals and bottle cages. The 140mm rotors softened the ungainly appearance of disc brakes, however there was still an excess of hardware when compared to conventional calipers. Indeed, the final presentation of the Roubaix Expert was missing much of the romance that I associate with road cycling by doing away with side-pull calipers.
Filling and bleeding the R785 brakes was a simple affair using Shimano’s TL-BT03-S kit, which comprises a syringe, reservoir, mineral oil and tubing. The process entails filling the system from the bottom up, to reduce air bubbles, then bleeding oil from the system from the top down until all air bubbles are gone (in absolute terms, it’s not possible to remove all air from the system, but it’s best to get as close as possible).
It’s important to remove the brake pads whenever working on hydraulic brakes, as any spilt oil will ruin them. At the same time, the pistons in the caliper need to be blocked because the pressure of filling and bleeding will push them out, preventing the pads from being installed. Shimano supplies a yellow block with the brakes for this purpose.
The reservoir simplifies filling and bleeding. Some levers are built with a small reservoir, but it takes up room, and in the case of a road lever, there is no space for it. In order to install the reservoir on the R785 lever, it must be disassembled a little, since the bleed screw is located under the silver nameplate. The screw that holds the nameplate in place is easy to locate after pulling back the rubber hood.
A 7mm spanner is required to open the bleed nipple on the caliper and then the syringe can be attached to slowly fill the system until the reservoir is about half-full. Once done, the bleed nipple is closed and the syringe is swapped for a waste bag to bleed the brakes.
There is something of an art to bleeding the brakes and it is best approached with patience. The bleed nipple is opened while squeezing the lever to expel air bubbles from the system. Knocking on the brake lines and the caliper will also help dislodge any air bubbles. Once the oil coming out of the bleed nipple is free of air and the stroke of the lever is firm, the process is complete. All that is required to finish the job is to lock the bleed nipple, remove the waste bag and the reservoir (a plunger is supplied to stop the oil from flowing out), and re-install the bleed screw along with the brake pads.
There are two adjustments for the brake lever: the reach can be adjusted with a screw at the top of the lever (hidden under the nameplate), while a second screw in the side of the lever body allows the stroke of the lever to be adjusted. Together, they provide a generous degree of adjustment that should suit a wide range of hand sizes, handlebar shapes, and braking preferences.
There is around 1mm clearance between the brake pads and the rotor, so the caliper needs to be positioned precisely in order to prevent any drag. Once set, there is no danger of the rotor rubbing the brake pads under load like there is for the rim and conventional calipers. However, without a convenient mechanism to centre the calipers, swapping wheels will always require extra time to re-position the caliper.
For more information on R785 brakes, see the Shimano website. Full instructions for installing R785 brakes can be found here.
It is unusual for conventional calipers to make much noise, though some rim and pad combinations can result in squealing under heavy braking. In contrast, disc brakes are well known for their high-pitched squealing, and the R785 brakeset was no different during the first few weeks of use.
The only remedy for new disc brakes is to use them so as to run-in the pads and rotors. Braking hard helps hurry the process along, but I was surprised at how difficult it was to find an excuse to use the brakes while out on the road. As a consequence, I was able to scare pedestrians and motorists alike with the sound of my braking at every intersection or set of lights.
The brakes were effective during the run-in period, but they lacked the kind of grab that defines hydraulic disc brakes. Once the squealing subsided though, I was pleased to find that the quality of braking also improved.
At this point, I tested the stopping power of the R785 brakes against conventional calipers by measuring the braking distance after travelling at 40km/hr. I initially tested two hand positions: braking while in the drops versus hands on the hoods. The R875 brakeset was compared with the Campagnolo Chorus calipers and alloy rims on my regular bike. The results are shown in figure below.
The braking distance (i.e. the distance required to come to a complete standstill) was measured for R785 disk brakes versus conventional calipers after travelling at 40km/h. Three hand positions were used: hands in the drops, on the hoods, and using one finger from the hoods. Each test was performed three times and the mean and SEM are plotted. The difference between disk and rim brakes during one-finger braking was statistically significant (*P<0.05, one-way ANOVA).
A lot of emphasis is placed on the power of hydraulic braking, but in this instance, conventional calipers matched the R785 brakes in their stopping ability. It’s worth noting that the test was conducted in the dry, and the weight of the two bikes was very similar: the Roubaix Expert Disc weighed 8.5kg versus 8.4kg for my Ridley Damocles.
While there was little difference in stopping power of the discs and conventional calipers, conventional calipers required much more effort. This was something that stood out for Andy in his initial review of the R785 brakes, which prompted me to test the braking distance when operating the levers with a single finger from the hoods. Under these conditions, the braking distance for the disc brakes was ~15% less than conventional calipers, as shown above.
Thus, while the hydraulic system doesn’t offer more power than conventional calipers, it is easier to access. As a consequence, I expect the R785 brakes will shine during long, technical descents by reducing or eliminating hand fatigue.
The R785 brakes offered plenty of modulation, with a smooth progressive feel that was very similar to my Campagnolo calipers. There’s little risk of sending yourself over the bars with these brakes because they are wonderfully predictable. And when coupled with their light action, the R785 brakes are almost intuitive in their responsiveness.
The R785 brakes performed as well in pouring rain as they did in the dry. There was no difference in the quality of braking at all, and as a consequence, I found myself riding almost as aggressively as I would on dry roads. In short, hydraulic disc brakes are without peer once the rain starts to fall and I really savoured the extra confidence they afforded.
As for the levers, the body largely resembles Shimano’s other Di2 levers, so they are slim and comfortable. The bulbous crown of the hoods recalls Shimano’s original STI lever shape, and just like the original levers, I could throttle them for a little extra leverage.
The Di2 system performed flawlessly, as expected, and proved to be the perfect compliment for the brakes. Indeed, the two systems combined seamlessly to enhance the quality of the cockpit controls, making for an effortless interface for the control of the bike’s gearing and braking.
MTBers have long enjoyed the benefits of hydraulic disc brakes. Indeed, hydraulic disc brakes have become ubiquitous OEM for all but budget MTBs. In time, the same may apply to road bikes. The benefits are obvious for cyclocross, gravel grinding, commuting, and endurance bikes.
What about racing? At present, there’s the extra weight to contend with and the danger of spinning discs, but the biggest obstacle is that the system complicates wheel changes. Perhaps electronics will be introduced to allow automatic re-alignment of the calipers after a wheel change?
Aside from the light braking action and outstanding performance in the wet, hydraulic disc brakes also benefit from a long service interval. In this regard, hydraulic brakes are a perfect compliment for electronic transmissions, which also benefit from a prolonged service interval when compared to their cable-operated counterparts. The two systems combine beautifully to improve the reliability and functionality of the bike, where the only casualty is traditional design.