Bytagand the publication "Disc braking for bicycles" route : the point in 2019"
Text: Guillaume Peephole – Photos: Orbea/ Pirelli / Mavic / Wouter Roosenboom / Irmo Keizer – Shimano / Christophe Guiard / 3bikes.fr
Sunday April 14, 2019: in the Paris-Roubaix finale, five of the six escaped riders ride with disc brakes. Such hegemony is a first at this level of competition, especially in Roubaix where the speed of repair in the event of a puncture is essential to performance. Moreover, Peter Sagan, last year's winner, was still skating in 2018, while he has definitely adopted discs for a few months, in all races like Roubaix.
Their use is no longer even discussed in mountain biking, or even in gravel or cyclo-cross, as they have changed the reliability and capabilities of these bikes designed to ride everywhere and in all conditions. It is also surprising to see that the only leading rider on the great cobblestone Classic to ride on skates is the former cyclo-cross world champion Wout van Aert. But it is true that he chose the worldtagand an additional brake lever on the top of the handlebars, a DIY impossible with hydraulic brakes.
The use of disc brakes is no longer even debatable in mountain biking, or even gravel or cyclo-cross, as they have changed the reliability and capabilities of these bikes designed to be ridden everywhere and in all conditions.
Contested in dry conditions, Paris-Roubaix is not normally the preferred terrain for disc braking. The race is held on almost flat terrain, and this is not where the superiority of disc braking over traditional rim braking is supposed to be expressed. Marcel Kittel was the first to pave the way in 2017, winning five stages of the Tour de France on a bike equipped with disc brakes – which was a revolution at the time. Except that the German sprinter had only won flat stages, switching to a bike with rim brakes as soon as the peloton approached the hill.tagne, an area where disc braking should normally show its superiority, if we are to believe the arguments of manufacturers and equipment suppliers.
Even though a number of teams and riders are still resisting, We know that there is a disc "lobby". The pressure is very high on the part of certain manufacturers, who would very much welcome the complete renewal of the fleet of bikes and wheels. And to speed up the movement, there is nothing like showing champions riding with discs whatever the conditions, even if for them the technical interest is not the most obvious.
The positioning of the disc "costs" from 2 to 4 watts at 45 km/h, depending on the wind angle. A slight loss that can be cancelled out with the use of a through axle without a lever. But in this case, an allen key is essential for the demontagand of the wheel, or a screwdriver for professional mechanics. Added to this are the problems of standards with different disc sizes and even their location on the hub. Troubleshooting in a few seconds is therefore more difficult to achieve, even if we know the adaptability of the mechanics of professional teams.
On the other hand, rim braking has also never been better, with stiff, light and reliable calipers, specific rubbers for aluminium or carbon that are ever more effective, and braking surfaces on carbon wheels that are finally reassuring in both dry and wet conditions. Equipment manufacturers continue to offer groups with both types of braking anyway.. On the other hand, when it comes to bicycle brands, the choice is starting to become more limited, with some models only offered with disc brakes. However, this choice is sometimes judicious for reasons other than braking, as we will see later.
Major developments
Some of the fatal flaws of the first proposed systems have recently been ironed out by the three major players in the equipment market.. With its DB system, Campagnolo limits the weight gain of groups equipped in this way, and installs small springs behind the pads that promote the return of the brake and limit friction noise during restarts or after heavy braking. Sram with its HRD system was the first brand to offer a contact point adjustment, to limit the dead travel of the lever before braking. Finally, with the latest Dura-Ace and Ultegra Disc, Shimano offers a beautiful integration of the oil reservoir inside the handle, so that it is identical or almost identical to the traditional system.
Major developments which do not change all the specific features of disc braking and which must be taken into account : the excess weight of the assembly, a slight loss of aerodynamics of the brake itself, recurring noises when braking, even when driving and extremely precise adjustment.
Specific equipment
You don't switch from traditional braking to disc braking with the snap of a finger. Bikes and wheels are specific, which requires a complete change of system, and the impossibility of reusing the old wheels. Frame and fork are reinforced to accommodate the calipers, located near the wheel axle, and to withstand the stresses of braking. The wheels are specific, because they receive the discs near the hubs. Here again, the stresses exerted during braking require stronger spokes, with more spokes and/or a different arrangement of them than thetage. As the rims must always support the pressure of the tires (no point in hoping for a spectacular weight reduction on this side) and powerful braking goes hand in hand with larger section tires, Disc wheels are about 200g heavier than traditional wheels. Thru-axles replace quick releases, for greater rigidity and to limit disc floating within the very small space between the brake pads.
A disc bike weighs 500 to 800 g more than its equivalent with rims of the same range.
A good frame for this type of braking must also be reinforced at the bottom bracket for uniform rigidity throughout the bike. This adds a bit more weight, as does the system itself. At Campagnolo, the excess weight of the calipers, handles and discs is approximately 120 to 240 g, at Sram and Shimano it is approximately 300 to 350 g.. Ultimately, a disc bike weighs 500 to 800 g more than its equivalent with rims of the same range.
This excess weight is painless or almost so in the very high end, because racing bikes remain restricted by the UCI limit of 6,8 kg anyway. A professional disc bike weighing around 7 kg is therefore common today.. On the other hand, at the entry and mid-range, the bill starts to be steep, and the extra weight adds to the more clumsy behavior of the bikes with accessories that also lack responsiveness. For sporty use, a disc bike weighing more than 8 kg becomes a handicap, and sometimes even disappointing, especially given the price-performance ratio that is unfavorable to the disc. Then, if the UCI finally decides to lower the weight limit for bikes (established almost 20 years ago), disc bike manufacturers will have a lot of trouble competing with rim bikes in certain conditions, for use in mountain biking.tagfor example.
More security?
Disc braking is powerful, progressive and insensitive to mud or humidity. Which normally reduces braking distances, both on dry and wet roads, while ensuring a constant slowdown which can conversely pose a problem with a traditional system, when the rim heats up, the pads wear out and the cable relaxes. Pads and discs are changed less frequently than brake shoes, and carbon rims are not exposed during every braking.
However, Braking power can also exceed the grip capabilities of the tires in certain conditions. To remedy this, manufacturers are offering bikes with wider tires. The bikes gain in handling route, but lose their nervousness.
Braking quality can be seriously affected on long descents, by maintaining pressure on the discs, which has the effect of making them heat up. Disc warping is therefore common after intensive use and a succession of heavy loads.
Discs therefore do not solve the problem of those who are afraid of picking up speed on mountain pass descents, where It is better to adopt aggressive braking, by slowing down very sharply when entering bends and releasing the brakes on straights. For braking that does not lock the wheels at the slightest action on the handles, discs adapted to the user's weight are required. On route The bikes are equipped with 140 or 160 mm discs, which differ markedly in terms of feel.
Discs don't solve the problem of those who are afraid of picking up speed on mountain passes.
Finally, there is the question of the prominence of the discs, which can be sharp in the event of a collective fall, especially after a long descent when the brakes have been heavily used and are overheated. But The real problem in the peloton is to be found in the cohabitation between discs and pads, since the followers of one or the other system do not adopt the same attitudes.
The hydraulic system
Maintaining the hydraulic system of disc brakes requires time and know-how. The advancetage of this system lies in the liquid installed in the sheaths, from the handle to the stirrups, instead of a cable. This fluid, activated by a master cylinder in the handle when braking, increases tenfold the force exerted by the fingers when braking. Hence an impression of smoothness and consistency in braking. The pressure of the fluid must be constant in the system, air or humidity must not alter the montage. The system may be weakened when transporting the bike, with leaks that can occur, making the braking inoperative, or if a handle is accidentally operated when empty, which has the effect of throwing everything out of adjustment.
The maintenance budget should not be neglected, especially since few practitioners are really able to do it themselves.
However, This system has also enabled other advances in terms of performance of the bike. Indeed, a hose with hydraulic fluid inside is much more flexible than a traditional brake cable with its sheath. The routing of the hose between the lever and the brake can thus be much more complex than with a cable, without altering the operation of the assembly, which allows it to be completely or nearly concealed through the handlebar, stem, head tube and frame or fork.
In this sense, disc braking allows:clean up the pilot stationtagand the most modern bikes, and to make them smoother and more aerodynamic. It was said above that the disc on the front wheel costs 2 to 4 watts at 45 km/h, but its montagand on some bikes, if it is still complex, allows you to gain watts elsewhere by eliminating aero drag from the sheaths on the front of the bike.
Not to mention that 12mm thru axles are much stiffer than a traditional quick release system, which has the effect of optimizing the connection between the frame and the wheels.
The records, yes, but…
Some of the most recent bikes, designed around disc brakes, are therefore extremely efficient, both in terms of rigidity and aerodynamics. Bikes with perfectly successful integration, and which will undoubtedly be able to benefit from the advances of a system which must still evolve in the near future to fill its few gaps.. But in this case you have to invest in very high-end bikes, the only ones that can compete in terms of performance with their rim-mounted counterparts at the moment.
To date and If we only talk about braking, the disc is superior to the pads, but not to the point of being a must for everyone and in all conditions. Because traditional calipers with good rims and good pads do the job very well, while being cheaper, lighter, easier to maintain and not annoying anyone with friction noises when dancing. Rather, it is for all the perspectives that the system as a whole can offer that it becomes interesting.The real revolution will be when a mid-range disc bike is as light and dynamic as its rim-mounted counterpart.
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