Trek trials disc brakes at the Vuelta - and reaction is positive from the pro riding them

Regarding the sharpness issue, I had a look last week at the disks on all the bikes in my garage, as well as the old rotors sitting in the spares box. Reckon there's about 15 years worth of MTB products represented there, mostly from Shimano, but a few other aftermarket manufacturers too.

The laser-cutting process used in disk manufacture can definitely result in some very sharp edges. A large scar on my brother's thumb is testament to that, where a workshop incident resulted in a big flap of skin being taken almost clean off the tip.

But the design has definitely improved in recent years, with the 'spokes' now largely being made of a separate forged piece of alloy with smooth edges, and the steel braking surfaces seeming to be less sharp than they once were. I'm not sure if they're grinding them, or cutting them using a different method, but they're not the razors they used to be.

Heat is a legitimate concern - I have met a mountain biker who has a nice 'brand' on his left calf which was a result of a crash at the bottom of a long descent. Some kind of lightweight guard might help here, and if designed with angled vents could even help channel cooling air onto the rotor. It's worth a thought.

With regard to the axle standards, the Eurobike displays seemed to suggest that 100x12 front and 142x12 rear is looking like the way manufacturers and teams are now leaning. A common standard in the peloton is a must, and the rest of the industry will follow. But from a consumer perspective, 100x15 front and 135xQR rear is going to be around for a while to come, simply because of it's long term use in the MTB industry. Those hubs aren't going to disappear anytime soon if you're happy with handbuilt wheels.

Putting an aerodynamic cover on a disc rotor would rather undermine the heat dissipating abilities of it.

One of the regular causes of crashes in the peloton is tyres losing grip under braking on wet roads. The carnage in La Course on the Champs Elysee was a clear example of this. Imagine how much worse it will be when everyone uses disc brakes.

The chain-line issue could be easily sorted by reverting to good old 10 speed!

Chainrings also do a pretty good impression of a circular saw when encountering soft fleshy bits - or are we going to ban them too?

I built my first disc-roadie over 10 years ago - the techs at big bike must be pretty cr@p if they're still working out the details like chainline and heel-clearances.

I'll stick to QRs for CX if it means quick wheel changes - fast rear wheel changes with a through-axle need 3 hands and easy to bork the thread if hurried. Rode an untabbed fork with discs for years and haven't died - Darwinian principles should sort out the rest.

Are brake rotors more dangerous than what is already on the bike? No.

Heat build up.
Most of the rear rotor is guarded by the rear triangle of the frame so contact in the event of a crash is remote. The front rotor may cause more of a problem as it is more exposed. However, you would have to drag the brakes for miles in order to creat enough heat in the rotor to cause serious burns.

"Bacon Slicer" Effect.
The rear rotor is guarded and front wheel carries less momentum than the rear and stops fairly quickly when in contact.

Now that we have looked at the 'danger' posed by disc brakes let's look at what is already there.
Put your bike on a work-stand and spin the rear wheel up. Now shove your hand into the wheel. Get a friend to collect your severed fingers and drive you to the hospital.

Can we now stop this bollocks about how more dangerous disc brakes are please. Thank you.

"It is clear from his reaction that the risk of a hot rotor scalding a body part in the event of a crash is still a big factor facing adoption among the pro ranks."

This is tosh. The chances of being burnt by a rotor in a crash are, I would suggest, absolutely tiny and the chances of having anything "sliced open" must similarly be vanishingly small. And irrelevant next to the road rash a crash is almost certain to produce. I realize road cyclists are hidebound but I hadn't appreciated just how superstitious they really are.

"However, covering the rotor, which he suggests as a solution, would only add weight back to the system, when there is already a weight penalty."

There isn't a net weight penalty. Manufacturers are able to build bikes that come in below the UCI weight limit (which is still at 6.8kgs I think) with ease, hence some rider having to add weights to their bikes. Less weights, more braking = same 6.8kgs. And that's even before you reduce rim weight because you don't need it to withstand braking forces/heat.

Is this a deliberate strategy of misinformation?

I've argued against whether disc brakes are that much better that rim brakes, they probably are, especially in the wet, but now I have a new question:

Do better brakes cause crashes?

Track racing has never allowed brakes because its reasoned they'd cause more crashes than they would stop. Thinking back to the tour, major crashes there were on straight roads where brakes weren't needed at all.

If you compare two extremes, one where the only braking is back pedalling and another where you can stop near instantly, if you were riding in two groups of each which do you think you would be more likely to end up riding into the back of someone?

Faster braking means you have to react faster and humans aren't evolving better reaction times.

Wheel changes will be a real problem though until agreed standards develop.
I find that whenever I have to remove and then reattach the disc wheels on my advanced pro I seem to end up with some degree of disc rub. I can be a bit of a klutz but I didn't have a similar problem with caliber brakes. I am using shimano hydraulics. Can any bike mechanics on here recommend a fail safe way to reattach a wheel,minimising the risk of disc brake rub?

@joulesr1975 - to be fair, there are very few cyclists who are as infuential as Spartacus and can actually choose what they ride. Most of them have only limited choice and everybody knows that.

I totally agree, however, that there were many unjustified statements from riders who have never actually used disc brakes.

The chainline issue is one I've heard from an engineer at a major components vendor. Not just the chainline, but the chain stays. To keep a racy short wheelbase with the wider hub of a disc brake on the rear can lead to heel clearance issues. So to get discs on race bikes may require compromising on wheelbase and speed of handling.

I think riders being cut by rotors is a bigger issue than burns. I wonder if the edges of rotors have to be so sharp. Couldn't they be given a round profile?

Rotors hurting someone in a crash .... no-one seems too bothered about a big circle with very sharp teeth in the form of a chain-ring!

My experience with thru axles and discs off road is that once the wheel is in, it's all lined up and easy to thread the axle in. So there's less faff and annoyance than my road frame which often needs nudging around and moving the brake callipers. I wouldn't be surprised if when the pro mechanics get handy at wheel changes with thru-axles, they'll be just as quick or quicker than QR systems.

My experience with thru axles and discs off road is that once the wheel is in, it's all lined up and easy to thread the axle in. So there's less faff and annoyance than my road frame which often needs nudging around and moving the brake callipers. I wouldn't be surprised if when the pro mechanics get handy at wheel changes with thru-axles, they'll be just as quick or quicker than QR systems.