Extreme downhill gradient, no braking effect. The brake disc wobbles and wobbles through the front brake calliper. The disc is ruined, the braking effect is gone. The horror scenario on an e-mountainbike. Reality in our practical test - and with a test rider weight of just 75 kilograms. Experiencing the total failure of a 180 mm disc is sobering. Admittedly, we imposed a tough programme on the brakes. The toughest test: repeated braking from 50-60 km/h to walking speed - on a road that winds its way downhill at an average gradient of 20 per cent. Tough, but realistic. Shimano's SLX, one of the cheapest brakes in the test, equipped with Shimano's Icetech technology, has done a good job up to this point. It was good on the trail, survived a grinding braking session without grumbling and was still running smoothly after 20 interval braking sessions. However, this changed abruptly after three more hard braking manoeuvres at high speed and the brake disc fell to its knees. Heat death. The Icetech technology is supposed to keep the brake cool.
The scenario from our practical test shows the relevance of the brakes on an e-mountainbike. Thanks to the motor assistance, we cover more metres in altitude in less time. Even less fit, heavier and less technically experienced riders can enjoy long and steep descents with ease. Added to this is the extra weight of around ten kilos that the E-MTB alone brings with it. All in all, the load on the brakes and discs increases.
One component is of particular importance: the brake disc. Klaus Liedler from brake expert Trickstuff puts the proportion of round discs in the performance of a brake at 40 to 45 percent. It is striking that the most powerful brakes in our test rely on thicker brake discs (2.05 and 1.95 mm) than the majority of the competition. The reason for this is that the greater the mass, the more heat the disc can absorb, which leads to greater stability. In addition to the mass, however, the surface area is also decisive, which depends not least on the disc diameter. "The brake disc must absorb as much heat as possible. The more surface area the disc has, the better it can dissipate the heat back into the air," explains Liedler. This equips a brake for sustained load. However, the disc diameter also influences the braking force. And here too, bigger is better. Because as the diameter of the disc increases, so does the lever and therefore the braking force. It is only logical that the first manufacturers are now equipping their E-MTBs with 220 mm brake discs.
Find out which of the ten disc brakes for E-MTBs performed well in the lab and in practice in our test report. The entire article with all test results including technical data and grades is available as a PDF in the download area below:
- Hayes Dominion
- Hope tech3 V4
- Magura MT8 SL
- Magura Trail Sport
- Shimano 501/520
- Shimano SLX
- Sram G2 Ultimate
- Trickstuff Maxima
- Trickstuff Piccola C41
- TRP G-Spec DH-R
