They are synonymous with speed: Carbon wheels. The aggressive appearance, the lush sound while pedaling, the envious glances of the club mates... there is probably no cyclist who can completely escape the fascination of the glossy fibre-circles. Often, however, the euphoria only lasts until the first braking action. "I've already twice ended beside the road and have so far gotten into several other risky situations", openly admits Juergen Falke, product manager at bike-giant Merida. "I wasn't used to this anymore. The last time, this happened to me, was back in the 80's when I was riding Campa's Delta-brake on firmly anodized aluminium rims - and back then, it was raining." Since, aluminium rim brakes have improved a lot: Stiff brake bodies with little bearing play, brake shoes whith adjustable angles, optimized pad mixtures, soft aluminium alloys and - above all - brake surfaces which are overlathed after bending and assembly, have lifted the brake systems to another level. The designers of carbon wheels, however, seem to have thought more about the appearance of the wheels than about their braking performance.
If you mount a carbon rim instead of an aluminium one, one and the same brake pads turn from obliging servant to bitchy sluggards. Quite often, the brakes hardly bite anymore, but squeal all the louder. They bite irregularly, are only moderately dosable and wear down very quickly.
Six manufacturers of brake pads especially designed for carbon rims sent their products in for testing. Partly, these were usual retrofit-pads for carbon-rims, others were especially made for certain rim types, as in the case of Campagnolo for example. The Italians even have developed two different kinds of pads - one for the in-house tubeless wheels and one for the clincher wheels. Also among the test-candidates: Corima's cork pads which have been the pros' favourites for ages. They have not only led to the carbon pads also being called cork pads, but became known to the broad public when they wore down Jan Ullrichs bike during a Tour de France stage to so much that he had to exchange it - and lost the stage.
The test: practical experience and laboratory
We combined the pads with different rims for some thousand kilometres on the road as well as on the test station in our laboratory. The practical riding tests were to inform us about doseability, noise development, wear and the brake forces the pads build up.
To cut it short: Compared with aluminium rim brakes, also the current generation of special carbon pads brakes only moderately on all test rims. Neither doseability nor brake performance withstood a serious comparison. The experiences on carbon were so manifold that a real buy recommendation cannot be given. A pad working on one rim without squealing for some hundred kilometres, failed on another.
Comparing the results nicely shows the felt diversity. Some pads can be acceptable on one rim and a catastrophe on another. There cannot be a winner, none of the pad-rim combinations only roughly gets close to the performance of usual aluminium rims. Put plainly: If the cyclist has to brake really forcefully, the brake path is approximately twice as long.
The situation is even more dramatic in combination with water. The first pull at the brake lever has hardly any effect. The cyclist must use more force which leads to the pad finding its way through the water film at some point. Often, this results in a jolt blocking the wheel in the case of aggressively biting combinations.
Author: Dirk Zedler