Technical FAQ: Can we make disc brakes safer?

Dear Lennard, With all the controversy about Fran Ventoso’s injury at Paris-Roubaix supposedly caused by a brake disc, I’m wondering if rim brakes are any different in terms of injury potential. Specifically, if I remember correctly, Joseba Beloki’s crash in the 2003 Tour de France was or might have been caused by a tire rolling off the rim, possibly because of high temperatures on the road, or possibly from overheated rims caused by heavy braking on the descent. I have had the experience on Mount Ascutney in Vermont of tubulars rotating on the rim because of the braking necessary — luckily never to the point of ripping the valve stem off, but making it necessary to stop and swap the rotation direction of the front wheel a few times on the way down. What do you think of this? Do the pros have that problem in races on hot days with long, steep descents?— Bob

Dear Bob, Yours was one of umpteen letters I got this week regarding Fran Ventoso’s Paris-Roubaix injury and road disc brakes.

You have a valid point; under some conditions, rim brakes have also been the cause of injuries. Yes, Joseba Beloki’s crash on that Tour de France stage into Gap was a function of his rim brakes. Locking the wheel up was the big problem; I don’t think he could have avoided the crash even if his tire had stayed on the rim. The rolled tire was a result of the combination of locking up his brakes, the wheel jumping up and landing hard at an angle, and the carbon rims being very hot, making the tubular rim cement more liquid.

I do think the brake locking up was a complete surprise to Beloki; he had not expected his brake to behave that way. The road surface had a lower coefficient of friction than he expected due to the high temperatures softening the asphalt, and when he touched the brake, the wheel started sliding. It was not entirely due to a grabby brake; we all know how easily this will happen on ice, even with the perfect brake. The road surface was not as slick as ice, nor was it as grippy as asphalt at lower temperatures. The brake pads were most certainly grabbier than normal, as the rim was so hot. The carbon brake pads of 13 years ago tended to not be as good at managing heat as they are now; 2003 was early on in the development of carbon rims and brake pads for them.

My guess is that, indeed, a disc brake of today would have greatly reduced the likelihood of this happening to Beloki. While the road would have been just as slick, his rim would not have been as hot due to braking. Consequently, his tire would not have been as hot and hence would not have been at such a high pressure, which would have given him marginally more grip. And with the disc brake, the cooler rim would have greatly reduced the likelihood of rolling the tire. However, had he locked up the wheel like that with a disc brake, I think he still would have fallen; once you stop a wheel and cross it up relative to the direction of travel at high speed like that, it is very hard to ride it out unscathed.

Carrying your argument further, the tires blowing in the heat on the stage 5 neutralized descent in the 2015 Tour of Oman were obviously a function of rim brakes. I went into great detail on that at the time.

As for the tire sliding around the rim from rim braking, I suspect that most riders with a lot of mountain miles on tubulars will have had this experience. I have had a valve stem tear on a tubular due to this, and the tire deflates very fast. I have also torn off valve stems on a number of occasions on clincher tires from the tire sliding around the rim on super-steep dirt while riding rim brakes, both on road bikes and on mountain bikes. I’m certain that none of these occurrences would have happened at all, had I had disc brakes. I remember descending the steep Silver Canyon Road from Mt. Whitney down to Bishop, California on mountain bikes on a hot summer day long ago. I was an early adopter with disc brakes and had no problems, and the guy I was with had rim brakes. …

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