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I know aero bars are considered unsafe for peloton, does this extend to disc brakes whose rotors can be hot and sharp? I'm not talking about races, just casual training rides: is it reasonably safe for others in the group?

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As for my safety I would be more concerned with the condition of their tires and bike in general and the skill of the rider. –  Blam Jul 28 at 12:56
    
"Image the guy in front of a group is the only one to have disc brakes and does an emergency stop."... cause of the 1955 Le Mans disaster (en.wikipedia.org/wiki/1955_Le_Mans_disaster) although that's not quite biking... –  dargaud Jul 28 at 14:32
    
"rotors can be hot and sharp". Caliper brakes also heat up, arguably they have less mass to absorb the heat with. All mechanical brakes work by converting kinetic energy into heat energy. Try touching the rim of a caliper brake bike after a downhill run. –  Aron Jul 28 at 14:53
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Disc brakes heat up on long heavy braking descents (especially when undersized) where the peloton would already have spread out and be running at a speed where a burn would be the least of their worries. –  DWGKNZ Jul 28 at 18:16
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If you're worried about disc brakes in a group, I think you have bigger problems to worry about (namely everyone else). In le mans, the drum brakes were far inferior to the disc brakes deployed - a good rim brake on a road bike is about as good as a good mechanical disc so the disparity isn't really there. –  Batman Jul 29 at 2:08

2 Answers 2

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I have never ridden in a peloton but I would say they should be not more unsafe than the chain blades that are already on your bike.

While riding, the only parts of your neighbour's bike that you would be able to hit should be the handle bar and maybe their pedals. Everything else is far less outstanding than those two parts and you should collide with your neighbours body before coming even close to say their disc brakes.

So the only real chance to hit someone else's brake rotors might be in case of a crash where you fall on their bike or their bike falls on you. In this case, there are a lot of parts on a bike that could give some bad injuries, for example the chain blades. And you will also hit the ground, so chances are high that you get injured by the fall as well. Adding disc brake rotors (which even are somewhat "shielded" by the wheel itself) might not add significant injury risk in this case. So I would consider them safe in these terms.

Another point that might be worth a thought is their performance. Image the guy in front of a group is the only one to have disc brakes and does an emergency stop. With their bigger brake performance they might decelerate much faster than the ones with the conventional brakes behind them, causing all others to hit him from behind.

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Yes, the main thing to ban from bunches is ... what was I saying ... yeah ... inattention. In a bunch you trust that the people ahead ride straight, call out stops / lights / turns / holes / doors / bikes / dogs / pedestrians / gravel / posts / tram tracks, and brake steadily, not accelerate too fast (unless it's a sprint point), and drop back to drink / eat / remove clothes / put on clothes. There are plenty of things on the list ahead of disk brakes to worry about. Just to complete the list, people at the back should call out when someone is dropped (social rides), and approaching traffic. –  andy256 Jul 28 at 10:03
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Any cyclist leading a line needs to be aware of those behind him when braking, and modulate his braking as conditions warrant. –  Daniel R Hicks Jul 28 at 11:26
    
Disc brakes are permitted in mountainbike racing, where riders would spend part of the race in close proximity. Excessive brake performance is only an issue if there are poorly maintained brakes in the group, or the conditions are wet. I would expect a well-maintained v-brake or dual-pivot caliper to provide sufficient braking in dry conditions. –  Emyr Jul 28 at 12:42
    
@DanielRHicks - Agreed I could make the peloton stack with rim breaks in wet conditions if I so choose. It's a matter of always being mindful that others are in close proximity. –  Rider_X Jul 28 at 17:29
    
@Emyr haha, banning disc brakes from mtb races would cause incomparably more injures than it can possibly prevent. –  alkar Jul 28 at 19:13

Disc brakes are reasonably tucked away on the frame and fork and as such pose relatively little danger relative to other components such as the large chain ring (which I have experienced in a peloton crash... Yay, stitches!). If you do experience complaints it would likely be either do to out of date rules or prejudices.

In terms of braking performance gap, I don't see this being a contributor to crashes as you should really never be using full brake power within a peloton setting. Braking should always be done with mindfulness of others and in a controlled fashion. If anything disc brakes provide finer control and could potentially be safer. In the situation of absolute emergency stops, yes you could out brake a rim brake in wet conditions which could cause a problem. However, if you are in the situation of an all out emergence stop within a peloton, something has already gone horribly wrong and really all bets are off in terms of outcomes. Under dry conditions I personally haven't notice any real world differences in total braking performance between road disc brakes and well set up rim brakes. Modulation, yes, but total power no. Maybe hydraulic discs would have a bit more power (I have only used cable disc brakes) but at some point you are hitting the traction limit of the tires and well maintained rim brakes should be able to do that in dry conditions.

As an aside, aero bars are considered unsafe due to the lack of fine control. Many riders drift in the aero position and tend to have slower response times. I have seen so many calamities over the years with people misapplying aero bars to regular riding (e.g., slow train track crossing!) I think most would be best to leave them at home unless on a dedicated TT course.

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