Since their first inclusion in professional races and domestic races a efw years ago the disc brake has always been a controversial topic of discussion. 

Depsite several bans in competition in both World Tour races and smaller domestic leagues throughout the cycling world, manufacturers continue to produce them and they continue to be adopted by leisure cyclists at an increasing rate. Manufacturers like Scott and Cannondale continued to produce disc road bikes in 2017 despite these risks.

Are they dangerous to riders? The main concerns are the risk they pose to riders in an accidents - namely the potential the spinning disc has to cut the rider or the heat generated by the disc to cause a burn.

One of the highest profile complainants in the professional peloton was Movistar's Francisco Ventoso who claimed a deep gash on his leg was caused when a disc rotar sliced him during a crash in Paris-Roubaix - one of the hardest one day races on the calendar.

Spinning Rotar=Razor

The discs that are used to provide better stopping power are designed to be air cooled to prevent them overheating and the hydraulic fluid from getting too hot, something that would affect performance. 

But how fast do they spin? They rotate with the wheel so the disc will be spinning faster in a descent or run in to a sprint which is when ost crashes occur. 

However in order to cause harm the disc would need to line up at the correct angle to the skin, something that in the chaotic nature of a crash isn't beyon the realms of possibility but you would have to be very unlucky to be injured in such a situation. 

How can the risk be reduced?

Many manufacturers are now manufacturing rounded edges to the brake discs used on their systems whcih makes it more likely that, should the disc edge come into contact with the skin, it will slide over rather than into the rider.

This has limited effect though as the discs themselves are usually no thicker than a spoke's width, so even a completely rounded edge would have a limited impact.

Disc Burn

Much more likely is the heat generated by the braking action causing a burn on the rider, although there is no case of this being claimed as reason for an injury in pro cycling.

As with any spinning disc, the amount of heat generated to stop a bicycle depends on how fast they are going and the weight of the rider, but given the low body weights of the professionals and the light weights of the machines the heat generated is more likely to be at its most dangerous when sprinting or descending. 

This is much more likely to cause an injury than a 'slice' from the disc edge as it's much more likely a rider will come into contact with the disc rotar in a crash than it is they will hit the rotar at such an angle to allow it to pierce the skin.

How can the risk be reduced?

Some manufacturers - including SRAM - have advised that they are looking into potentially creating a cover for the rotar to protect against the threat of cutting an d burning, but this would need significant research and development to prevent it from affecting performance.

So, Are Disc Brakes Dangerous?

As with any element of cycling there is the potential to injure with disc brakes; but the risks aren't especially prominent in this case. 

The same 'cutting' argument could be said of chain rings which are effectively spinning cogs with teeth and have the same potential to injure riders in a crash.

The fact is that cycling can be dangerous. Descending down mountains at almost 60mph on a bicycle is inherently dangerous and the likelihood of being injured by a disc brake is minimal in comparison.