I'm in favour of road discs not for more stopping power but more consistency in the wet, no more rim wear, no worries about over-heating rims (more of a concern with tubs), better performance for carbon rims and better modulation.

In dry conditions more power isn't needed but in the wet it would be nice to have nearly as good braking as in the dry (it's a long way short with rim brakes). I'm not sure over-heating of discs would be an issue either, speeds are much higher to help with cooling but also most road braking is done in short bursts rather than dragging the brake as can often be the case on MTBs. If cable disc brakes can be done with enough power and modulation then there would be no need to worry about over-heating the oil in the calipers either.

I think the main barrier is just all the changes and testing it would need (new hubs/rims, seat stays beefing up, forks beefing up, new caliper/rotors etc.) it just isn't worth the industry investment for the relatively small advantages it would bring.

moved to disc brakes in a heart beat the second they were mainstream and viable on MTBs but proper road bikes? I can see it on loaded up tourers and even cross bikes but 23c tyres on a racing bike really can't cope with any more braking power than a quality calliper already offers. It's easy enough to lock the brakes as it is!

Why do people make categoris statements like this with no datqa whatsoever to back it up?

…and what aracer said re locking front wheels, I'd love to see it.

cynic-al,
Isn't what you're saying here that the force required to knock you over the bars on a road bike is much lower than on tourer/tandem/mtb?

Must admit, didn't really get aracer's point, but what I think you're talking about is that you think it's nigh on impossible to lock a road bikes front tyre.

I think this is probably much more a result of the rider's centre of mass being high up. As a result the resultant moment from braking forces is amplified, making it much more likely to pitch you over the bars before the capacity of the tyre is reached.

Like I've said before, not against discs on a road bike in any way, but to defend what other's have said about 23c tyres not being able to 'take' disc brakes. They do have a good point with regards to tyres skidding etc. especially at high speeds when the forces required to pitch you over are much higher.

Si C

All your hypothesising is great Si C (SimonC?) but I've never seen anyone lock their front wheel on a road bike (and my point is I don't think it's possible or useful) – and I'm scared to try.

I think this is probably much more a result of the rider's centre of mass being high up.

You have seen a road bike haven't you – lower BB, lower front end, lower position?

In any case becuase a stronger brake not only allows greater braking forces (subject to traction as you correctly point out) but allows better control of braking, less fatigue etc.

Theres not actually any hydraulic road brake levers out there yet.

AFAIK Magura made a short lived version of their hydraulics with road levers, admittedly rim, not disks – called HS-66's and HS-77's. They're discontinued and consequently as rare as rocking horse poo but apparently they still pop up now and again on ebay…

I've skidded my front wheel in an emergency stop – from 50mph, down to 10ish (corner tighter than I remembered) in a very short amount of time.

Surely whether you go over the bars or skid just depends on if you keep your weight back when you use the front brake. On any well set up bike it will be possible to make the back wheel go up in the air if your weight is forward, and possible to skid the front wheel if you keep your weight back. If bunging on the front brake just chucked you over the bars, there'd be no way to brake sensibly when going downhill or going fast. The front brake = over the bars thing is surely only if you're not very good at braking?

Joe

Have always liked the idea of small discs on a winter road bike and toyed with putting some (mechanical) ones on my ticross which does winter road hack duties as well as touring and CX. In the end itwas the faff of making them work with a rack that put me off.

For me it would be about rim wear and longevity. On a 3 day tour fully loaded in the rain in the hills I went through a set of pads in a day and was worried about making it back.

On a race bike the other problem might be the slightly longer time to get the wheel on and off, aligining the disc between the pads in the even of puncture. Something the XC mtb boys must have perfected I guess.

Why do people make categoris statements like this with no datqa whatsoever to back it up?

…and what aracer said re locking front wheels, I'd love to see it.

What data do you want? I have decent rim brakes that if I so chose, can apply too much power – what data do I need to qualify myself to partake in this debate then?

Technically if your front pitches you over the bar, the wheel has locked to do this no? Why do you assume locking = skidding? *sigh*

I think it could happen for high-end road bikes – for touring/commuting/ recreational riding as many have already pointed out it already exists. That's all been elaborated well by those above but I think there could be additional benefits for racing which haven't been touched on.

It's all about wheels. The lightest, fastest wheels these days are tubs on carbon rims. These are fantastic; light, stiff, fast rolling – but they have one (potentially literally) fatal flaw – braking. Carbon rims build up heat and don't dissipate it so quickly as metal rims. This not only imparis braking performance, but also means on a long alpine descent rims can heat to a point that softens tubular glue and it becomes more likely to roll a tyre (see Joseba Beloki in the tour 2003) which gets ugly fast.

Discs would give you the assurance of consistent braking (let alone when wet) without the concern of overheating rims and rolling tyres. Descents could be faster knowing that you can brake late and hard with confidence, not have to back off in order not to overheat brakes.

It certainly could be done with the technology available, whether it actually happens is another question, roadies are a conservative bunch and it'd likely be outlawed by the UCI (if in fact it's not aleady) before it even got off the ground.

I've locked the front up on my road bike, more becuase it was wet and the blocks snagged on a worn rim than becuase of pure braking effort. I was in the drops, locked, lost balance, got off the brake and just failed to wrench balance back in time, so I hit the deck. Hard.

Never managed to lock the front JRA, even with shimmy dual pivots and anchor like fibrax red pads.

As for people talking about the discs boiling on alpine descents, when racing you don't drag the brakes that much. Even descending big alpine passes in a steady peloton on narrow twisty you only need to take a little energy out to stop you ruinning into the guy in front. If the road off the top is wide, you can pretty much stay off the brakes and only feed them in for big corners, which is exactly what discs are good at.

I can see them coming in if they start to develop road disc specific systems.

I betcha that in a few years time they'll have itsy-bitsy lovely wee disc brakes. It will happen.

When I brake hard on the road bike I do find myself easing my bum off the back of the seat to prevent myself going over the bars – and that's with 120psi in the tubes.

It's probably either because I'm a mountain biker or because I'm rubbish

"disc brakes and QR levers at 50mph? thats going to seriously hurt"

nah… it won't be likely to eject as the contact patch of the tyre isn't going to allow enough force. it's a heat build-up and modulation issue, not power – a road disc would have advantages in reducing rim heat allowing lighter rims etc. also lighter stays could add comfort and light forks are already getting stiff enough to cope.

Shimano have the STI technology already in the Dual Control lever – it could be closer than you think.

Was Lance advocating the use of discs on road bikes? As L.A has a stake in SRAM I wouldn't be surprised if SRAM are soon to be launching a new road groupset including disc brakes!!

Mr Cynical 🙂

You have seen a road bike haven't you – lower BB, lower front end, lower position?

All very true, but the bike itself is a tiny proportion of total mass, the rider is generally in a raised position to increase pedalling efficiency, it's true they are bent over to increase aerodynamic profile, but they're COM is still in an elevated position compared to a mountain bike rider etc. etc.

Anyway, as many have pointed out in my absence, clearly poss to lock the wheel with calipers but all depends on conditions, riding position etc. etc.

The numerous benefits of discs have also been stated clearly. I think it'd be a great idea on tour stages with big hairy descents, as has been pointed out, all a question of regulation. If it can be proven they are effective and safer then why not.

GaryLake – Member

What data do you want? I have decent rim brakes that if I so chose, can apply too much power – what data do I need to qualify myself to partake in this debate then?

you wrote this, a statement of fact, with nothing to back it up – that's my point.

23c tyres on a racing bike really can't cope with any more braking power than a quality calliper already offers

And

Technically if your front pitches you over the bar, the wheel has locked to do this no? Why do you assume locking = skidding? *sigh*

I guess if you need to argue semantics then you've already lost. *sigh*

My saddle is 2cm higher on my road bike than on my mtb. I'll bet that the combination of lower BB and much flatter back position means that my CoG is lower on my road bike than on my mtb.

I don't know what to say cynic-al lol

Ignoring that, I can see people's points about rim development and how discs would allow that.

Maybe so clubber, but when you're sat up on a mountain bike you're also bringing the position of the COM further back, therefore increasing the moment exerted by your weight (action of gravity). It may therefore be harder for you to pitch over the bars comparatively.

This fixation on skidding/pitching is a very complicated story, and a tricky dynamical system.

For example, as you beging to pitch, the moment through gravity decreases and the moment from braking increases. This is because you're moving up and forward. Combine this with the increased contact force on the front tyre and the capacity of the tyre correspondingly increases.

I'm trying to paint a picture of why this may happen and what's going on. I'm not giving a definitive ranking table on pitching probabilities and COM position.

I'm beginning to see why so many needless pompous arguments on here continue ad infinitum.

Can't help feeling the major point is being missed; on a road racing bike, you don't need to brake to the same extent as a mountain bike.

It's racing.
Fast is good.
Stopping on a sixpence is simply not required.

In addition, unless every bike in the peloton is equipped the same way, any disparity in braking ability will cause crashes.

…and the carbon rims overheating on descents thing applies to aluminium rims with tubs too…

I might as well add my bit. Disks on road bikes would be great, I do d lot of muddy back lane commuting and go through pads and rims pretty fast, would love a fast bike with the ability to run disks.

Too powerful is nonsense, if the lever feel is good and sensibly modulated there is no such thing as too powerful, only idiots who pull the lever too hard. MotoGP brakes are far too powerful, as witnessed a couple of years ago when one of the Ducati boys flipped himself onto his head when the brake lever caught another bike, but the ability to brake with a light pressure applied by a single finger is less fatiguing. Anyone want to go back to having to yank the lever with three fingers on an MTB? Modulation and feel is the key.

If the UCI get their head out of their arse disks will be coming to roadbikes purely on aerodynamic grounds. Can't wait.

Wouldn't the point of running discs on a road bike be that you could build more exotic wheels due to the lack of need for braking surface?

Swapping rotating weight for non-rotating weight strikes me as a good idea.

non rotating discs? Cool!! 😆

mincing off road is one thing, but worrying about brakes on a roadbike? 🙄 what a bunch ay fannies!!

If the UCI get their head out of their arse disks will be coming to roadbikes purely on aerodynamic grounds.

Given disc brakes would be less aero, how does that work?

I'm beginning to see why so many needless pompous arguments on here continue ad infinitum.

Because people who don't actually understand the issue properly attempt to theorise and argue with those who do? 🙄

The pitching over thing is pretty straightforward. Any normal position on a bike – road or mountain bike position, I'm only excluding things like recumbents or easy riders here (and of course tandems – they do skid the front wheel) – the CofM is high enough that you'll pitch over the bars if you pull the front brake on full on normal tarmac with any decent road tyre. That's assuming a front brake strong enough to lock the front wheel, which any normal road caliper is.

The confusion is all in the initial statement about disc brakes being too powerful for skinny 23mm road tyres. The implication being that they're not too powerful for all the extra grip you get from fat MTB tyres. The problem with that (I'm sure this will provoke lots more disagreement) is that you don't actually get more grip from MTB tyres, you get less! Either off-road because of loose surfaces, or on road because of squirm (though on normal dry tarmac you should have enough grip from any tyre to pitch over). Hence why in some circumstances you can skid the front wheel on a MTB – nothing to do with CofM.

If (when) they bring road racing disc will they be carbon so that they can be moulded as one with the hub?
Aren't disc currently not allowed in top end cyclo cross? when they allow this i recon that the road can't be far behind.

~has images of TDF mechanics with scolds up their arms trying to change wheels as quickly as possibly~

UCI should just lower the weight limit. I think it's crazy that the ladies have to have bikes also with the same weight limit… just think how many weights they have to add.

6.8kg is the set limit so that the bikes can withstand the rigures of racing, going any lighter will compromise strength and the safety of the riders, which is of course paramount. If you've ever picked a bike up weighing 6.8kg, you'll soon realise it's very light. Most of the riders bikes are usually around 7.0kg+ anyway.

Discs brakes aren't used because the injuries resulting from their use would be pretty serious, eg: fingers comming off (160 rider peloton bar to bar, tyre to tyre). The majority of the bikes wouldn't be able to withstand the force either. That and the fact they aren't needed..

Ciao 😉

6.8kg is the set limit so that the bikes can withstand the rigures of racing, going any lighter will compromise strength and the safety of the riders, which is of course paramount.

Does that mean the bikes which had added ballast to make the weight limit weren't safe? Is my UCI illegal bike unsafe?

Most of the riders bikes are usually around 7.0kg+ anyway.

Maybe the normal day to day bikes – I very much doubt any of the top 10 in the TdF were riding mountain stages with bikes that weighed any more than 6.81kg. I don't suppose Emma Pooley's bike ever weighs more than 6.81kg.

The ballast which are sometimes added, make up the couple of hundred grams that a bike could be under, it's not like they're adding a kilo to a bike that weighs 5.8kg.

As for the weight of the top-10 riders bikes, I'd agree with that they're all going to be use as light a bike as possible. But then that opens up the can of worms of power/weight/watts Vs weight of a bike argument, which some hsay the weight of the bike makes next to no difference, so in theory a top rider could ride a 25lb steel bike, and still be up in the GC…yeah. 😐

this point about injuries is a nonsense.

When has anyone heard of similar injuries being caused by spokes? Never, because riders do not fall into each others wheels. Even if they did, simple fairings could avoid this.

Am also loving the armchair experts who "know" the frames couldn't withstand the forces. You designed them did you? Oh….

What about the dishing of the wheels? Surely adding a disc to already very narrow wheels would result in the spokes being almost vertical making for a very flimsy wheel?

Am also loving the armchair experts who "know" the frames couldn't withstand the forces. You designed them did you? Oh….

and you know enough about their design/construction to say they are wrong?

cynic-al – Member
this point about injuries is a nonsense.

When has anyone heard of similar injuries being caused by spokes? Never, because riders do not fall into each others wheels.
I agree with this also there is a chainset spinning round that has a nice sharp toothed edge to it and that isn't seen as a problem and don't tell me that the riders leg protects others from it as that would only be true for part of the rotation.

Best thread in ages. Good work fellas!

what if the bike was on a treadmill going at same speed in opposite direction would the bike take off?

chunky_pott – Member
What about the dishing of the wheels? Surely adding a disc to already very narrow wheels would result in the spokes being almost vertical making for a very flimsy wheel?

Road front wheels are the same hub width as mtbs. Road rear wheels are 5mm narrower at the hub than mtbs. 5mm at the rear is not enough to make the spokes vertical if a disc was fitted.

What about the dishing of the wheels? Surely adding a disc to already very narrow wheels would result in the spokes being almost vertical making for a very flimsy wheel?

Road front wheels are the same hub width as mtbs. Road rear wheels are 5mm narrower at the hub than mtbs. 5mm at the rear is not enough to make the spokes vertical if a disc was fitted.

thats assuming your going to use the same hub/fork/disc standards as mtb's. If road specific disc systems do get developed you can bet your house they wont be using the current 'IS' dimensions, so wheel dish will not be an issue.

I love the idea that the main thing you'd be worried about in a 150 rider pile up at 40 miles an hour is little disc brakes – I'd be a bit more concenred about the ground!

Because people who don't actually understand the issue properly attempt to theorise and argue with those who do?

I wouldn't say you're completely without understanding 😉

Anyway, I think this is the stage when we agree to disagree.

Tara