Small brake discs in a complicated sandwich design, brake pads with cooling fins, a new mounting standard: Shimano has invested a lot of energy in recent years in improving the brake discs.Hydraulic disc brake on a road bike to establish the company. However, the endeavours were also accompanied by severe setbacks. Suddenly dwindling braking performance due to outgassing pads (TOUR 11/2013) or total failure of the Ice-Tech brake discs under high loads (TOUR 6/2014) are just the most serious problems that TOUR brought to light with intensive tests. The additional weight and higher maintenance costs compared to rim brakes still make buyers hesitate; the fact that the discs react very sensitively to external influences by squeaking loudly annoys many road cyclists who already ride disc brakes.
Delay
Many manufacturers and cyclists are therefore eagerly awaiting the new disc brakes, especially from the Ultegra R8000 road bike groupset - in the hope that the teething troubles have been eliminated. But Shimano is struggling with delivery problems. The parts required for the Dura-Ace R9100 announced in spring 2017 was months in coming, many bike manufacturers were unable to deliver their top models. The first test bike with the Dura-Ace disc brake was not available to TOUR until late summer. Now the Ultegra is also already behind schedule - it was announced for June, the first parts have been available to buy since autumn. We can only speculate about the reasons for the delay, Shimano is keeping quiet.
About the technology: The lever shape is based on that of the rim brakes, but the lever bodies are slightly thicker and higher due to the integrated hydraulics and are not quite as hand-friendly. The braking performance is comparable to the previous BR-RS805 hydraulic brake, which is not assigned to a group. There's nothing wrong with that - even compared to the disc brakes of competitors from Campagnolo and SRAM, Shimano currently builds the most powerful road bike brakes. In order not to push the heat-sensitive sandwich discs - a composite of an aluminium core with stainless steel braking surfaces - to their limits, large aluminium cooling plates are now integrated to dissipate as much heat as possible into the airflow. While the cooling plates on the Dura-Ace discs are painted black, they shine silver on the Ultegra discs. The fact that the new brake is actually more stable as a result was tested by our First endurance test with the Dura-Ace disc brake already shown. For a system weight (bike plus rider and any luggage) of around or slightly over 100 kilograms, at least the discs with a diameter of 160 millimetres can be considered reliable even on steep descents. Although the collapse of the system due to extreme heat cannot be completely ruled out - which also applies to rim brakes or wheels braked with them under appropriate load - the possibility shifts to a range in which system weights of 140 kilograms and more would have to encounter an extremely long, steep descent and continuous or grinding braking. The discs can also warp in extreme heat and then rub against the pads.
Problems with the heat
However, the system shows weaknesses under high loads: From a temperature of around 200 degrees Celsius - which can occur during a long descent if you let the brake drag or brake hard several times in succession - pronounced fading sets in and the brake loses around 30 per cent of its performance. This is a known phenomenon that only occurs once; it could be avoided if the brakes or pads had already been braked or otherwise heat-treated by the manufacturer. If you are aware of this phenomenon, you can adapt to it and apply the brakes yourself. In our opinion, however, this is a product characteristic that is not adequately communicated by the manufacturer and should not be the responsibility of the end user.
Test summary of the Ultegra disc brake
The new Ultegra brakes of the R8000 groupset are significantly more heat-resistant and therefore just as reliable as the solid steel discs of the competition. Compared to the rim brake, the disadvantages are the higher weight - with filled hydraulic lines it should be around 200 grams - as well as the more complicated installation and maintenance. Our tests have also shown that another problem remains: One of the brakes squealed extremely loudly even when braking weakly, and the noise could not be finally eliminated either by cleaning the disc or by replacing the pads. The racing bike world will therefore have to continue to wait for a disc that does not immediately counter the undeniable advantages of disc brakes with new disadvantages.
How TOUR tests road bike disc brakes
Laboratory test on the TOUR brake test benchWe test the front brake with the associated lever and cable on an aluminium rim. The braking forces are measured in dry and wet conditions, and it is also determined whether the brakes tend to "fade", a reduction in braking force, when they heat up. The dosability, which depends on the entire transmission path (brake cable), is also recorded.
Jens Klötzer
Editor
