Disk or Rim

DeVlaeminck

I'm still not convinced about disks - I've got HyRds and apart from being more to get wrong with them (and there's a thread on here with plenty of people having difficulty getting them working right) even when they are working right I don't find them any better than rim brakes - in fact in the dry I prefer the feel of a decent rim brake with swisstop pads.

No I haven't used full hydro but last time I was in the Alps the guy last to the foot of every descent was the guy with hydraulic disks so they aren't going to transform your descending. It would interesting to see the pros riding the Tour with a mix of disks and rim brakes because if they make that much difference we should see it on some of the technical descents.

The Rookie

Stueys wrote:

the slight gain in weight (which is already being nullified as the engineers work their stuff).

There will always be a gain in weight.

More material in the hub to mount the disc and the disc will always weigh more than a rim braked wheel with about 20g extra in the rim to allow for wear.

The lever is slightly heavier, the hose/fluid is slightly lighter than the cable inner and outer (a lot less advantage for decent routing that minimises the heavier outer cable) and the wheel calliper about the same weight.

meanredspider

DeVlaeminck wrote:

No I haven't used full hydro but last time I was in the Alps the guy last to the foot of every descent was the guy with hydraulic disks so they aren't going to transform your descending. It would interesting to see the pros riding the Tour with a mix of disks and rim brakes because if they make that much difference we should see it on some of the technical descents.

Yeah - I don't think an N=1 is any sort of data on which to draw a conclusion. It's the same as in the Faster Bike thread that the guy on the heavy CX bike was first to the top of the climbs: doesn't tell us that CX bikes are what climbers should use.

Put the same person on the two bikes and see which is faster begins to be a better test. I know I can brake later and harder and with more confidence & control on disc brakes than I can rims which means I'm a faster descender on discs. YMMV. I know, however, from experience that I'm a quick descender. I'm big which means I accelerate downhill fast naturally and that's combined with a good understanding of lines and braking. I need something to counter my poor climbing speed.

stueys

meanredspider wrote:

DeVlaeminck wrote:

No I haven't used full hydro but last time I was in the Alps the guy last to the foot of every descent was the guy with hydraulic disks so they aren't going to transform your descending. It would interesting to see the pros riding the Tour with a mix of disks and rim brakes because if they make that much difference we should see it on some of the technical descents.

Yeah - I don't think an N=1 is any sort of data on which to draw a conclusion. It's the same as in the Faster Bike thread that the guy on the heavy CX bike was first to the top of the climbs: doesn't tell us that CX bikes are what climbers should use.

Put the same person on the two bikes and see which is faster begins to be a better test. I know I can brake later and harder and with more confidence & control on disc brakes than I can rims which means I'm a faster descender on discs. YMMV. I know, however, from experience that I'm a quick descender. I'm big which means I accelerate downhill fast naturally and that's combined with a good understanding of lines and braking. I need something to counter my poor climbing speed.

Agree, that's more conclusive. To be honest I don't push my descending to the edges of grip where better braking is going to make a huge difference, I'm relatively quick but there are quicker. In terms of confidence my discs are top as they behave the same way every time, quickly followed by swiss stop on alu rims (whilst it's dry) and my carbon wheels last (the pads can be a bit grabby on those and we won't discuss wet weather braking).

The big advantage for me with disc braking is the consistency and modulation. Consistency in that the brakes performance doesn't degrade dependent on conditions, I have to significantly reduce speed on my carbon rim wheels on wet descents. Likewise the modulation on the dics brakes lets you go to the edge of traction more readily than with rims, though a set of swiss stop on alu rims is close.

Alex99

Imposter wrote:

Alex99 wrote:

Imposter wrote:

thecycleclinic wrote:

I ride everyday on disc brake and on sundays race I could have done with disc brakes. I would have been able to brake later into the bends and maybe come out of the last bend a couple of places higher with a point or two more.

Presumably all riders were on calipers and it was the same for everyone - which makes that argument completely redundant.

Are you suggesting that a rider can't take advantage of better braking or grip in a race?

What advantage is there when all riders are currently required to be on the same brake type? If everyone had been on discs, the issue would be exactly the same and he would still be no better off. He would only have an advantage if he was the only one riding discs and everyone else was on calipers, which is currently not within the rules as they stand.

True, it's theoretical at the moment because you can't race with discs. But, you're missing the point. thecycleclinic can still legitimately say "I could have done with disc brakes". He's using an example to point to some advantage of discs over rim brakes. If discs do become race legal, then not everyone will have them immediately and then there may be an advantage over differently equiped riders in some situations. People will still be asking what they should go for, just like they are here.

imposter2.0

Alex99 wrote:

Imposter wrote:

Alex99 wrote:

Imposter wrote:

thecycleclinic wrote:

I ride everyday on disc brake and on sundays race I could have done with disc brakes. I would have been able to brake later into the bends and maybe come out of the last bend a couple of places higher with a point or two more.

Presumably all riders were on calipers and it was the same for everyone - which makes that argument completely redundant.

Are you suggesting that a rider can't take advantage of better braking or grip in a race?

What advantage is there when all riders are currently required to be on the same brake type? If everyone had been on discs, the issue would be exactly the same and he would still be no better off. He would only have an advantage if he was the only one riding discs and everyone else was on calipers, which is currently not within the rules as they stand.

True, it's theoretical at the moment because you can't race with discs. But, you're missing the point. thecycleclinic can still legitimately say "I could have done with disc brakes". He's using an example to point to some advantage of discs over rim brakes. If discs do become race legal, then not everyone will have them immediately and then there may be an advantage over differently equiped riders in some situations. People will still be asking what they should go for, just like they are here.

Leaving aside the legality issue, just consider the bunch dynamics for a second. Riders in a bunch generally slow at the same/similar rate into corners. If they didn't (and they sometimes don't) there would be carnage. Try to picture the image of cycleclinic, in a bunch, not slowing down when everyone else is. It's not a good picture.

Alex99

Imposter wrote:

Alex99 wrote:

Imposter wrote:

Alex99 wrote:

Imposter wrote:

thecycleclinic wrote:

I ride everyday on disc brake and on sundays race I could have done with disc brakes. I would have been able to brake later into the bends and maybe come out of the last bend a couple of places higher with a point or two more.

Presumably all riders were on calipers and it was the same for everyone - which makes that argument completely redundant.

Are you suggesting that a rider can't take advantage of better braking or grip in a race?

What advantage is there when all riders are currently required to be on the same brake type? If everyone had been on discs, the issue would be exactly the same and he would still be no better off. He would only have an advantage if he was the only one riding discs and everyone else was on calipers, which is currently not within the rules as they stand.

True, it's theoretical at the moment because you can't race with discs. But, you're missing the point. thecycleclinic can still legitimately say "I could have done with disc brakes". He's using an example to point to some advantage of discs over rim brakes. If discs do become race legal, then not everyone will have them immediately and then there may be an advantage over differently equiped riders in some situations. People will still be asking what they should go for, just like they are here.

Leaving aside the legality issue, just consider the bunch dynamics for a second. Riders in a bunch generally slow at the same/similar rate into corners. If they didn't (and they sometimes don't) there would be carnage. Try to picture the image of cycleclinic, in a bunch, not slowing down when everyone else is. It's not a good picture.

In the case of a tight group, I'd agree, you generally do have to brake at the pace of the group. But, I've been in much more ragged race situations, often in the wet or on gravel strewn roads, where there is opportunity to gain position. Anyway, wasn't it just a comment to illustrate a point that discs could offer more control and not whether should I get discs for racing?

imposter2.0

Alex99 wrote:

Anyway, wasn't it just a comment to illustrate a point that discs could offer more control and not whether should I get discs for racing?

Well yes, it probably was. But it was a crap analogy, that's all.

Alex99

Imposter wrote:

Alex99 wrote:

Anyway, wasn't it just a comment to illustrate a point that discs could offer more control and not whether should I get discs for racing?

Well yes, it probably was. But it was a crap analogy, that's all.

Hey ho. Is Imposter having a good day?

imposter2.0

Alex99 wrote:

Imposter wrote:

Alex99 wrote:

Anyway, wasn't it just a comment to illustrate a point that discs could offer more control and not whether should I get discs for racing?

Well yes, it probably was. But it was a crap analogy, that's all.

Hey ho. Is Imposter having a good day?

Today is fine. Although I can't remember what mood I was in 12 days ago, when I made the original comment.

pilot_pete

Carbon rims with hydraulic disc brakes. A match made in heaven. I'll never go back.

Advantages?
1. Better stopping power (even than the best rim brakes I have owned - Dura Ace and Record)
2. The same performance in the wet (which no rim brake has full stop)
3. Better feel and modulation than a rim brake (note I said 'better', not that you can't modulate rim brakes)
4. With hydraulic discs I can apply full stopping force from the hoods which you simply cannot do with a rim brake.
5. My rims will NEVER wear down - my winter bike is now 5 winters old. The rims look like new, the discs are still the originals and I have changed pads 3 times.
6. Despite what those who have forked out for carbon rims and are defensive will say, carbon rimmed caliper braked wheels offer sh1t braking performance compared to disc brakes. They grab with expensive pads and stop in the dry, but can overheat and delaminate (and don't try to say it is all down the operators braking technique as that is their 'excuse' for poor design and materials compatibility) or melt the resin which resets and leaves hard spots on the brake track thus trashing the rim. I have seen this on 4 pairs of wheels that I and 3 mates own. All different brands from Reynolds (supposedly one of the best) through to imports. As for wet performance, they are simply 4th division compared to premiership discs.
7. The feel is better. I mean the lever action, the lack of cable resistance, no grabbing or dead spot (wiping water off wet rim), predictable, the same every application, no grit sounding like it is grinding your rim away or aluminium shards in the pad against the rim.
8. Pads are easier to replace and absolutely no setting up is required at all - they are either 'fitted' or not, unlike a rim brake, especially with a rim with a small braking track where they need to be precisely set. Yes I know it is not difficult to do, my point is changing disc pads is simply easier...

Disadvantages?
1. Heavier. So what? It is not like they are hugely heavier. Makes no difference to me, I am actually climbing quicker than I was previously on rim brakes, but that is more down to other factors. The weight is not noticeable to me.
2. Less aero. Do you really think it makes a difference to a weekend warrior on his road bike? First thing I would change is riding position if you want to get more aero, not disc brakes :roll: so I won't be looking for disc brakes on my TT bike where they would be slightly detrimental, but my road bike, come on it is about braking performance not arse up head down everywhere I go.
3. More 'complex'. Maybe so, but these days most items are throw away, so if a brake/ shifter develops a fault the chances are you just have to replace it - the complexity of the gubbins doesn't really come into it if they are non-serviceable. I have installed hydraulic discs during two bike builds and it is not difficult. Bleeding is simple with the correct tools, as is fitting hoses.

A hydraulic disc brake that fails roadside is no less repairable without the correct replacement parts than a rim brake. I would rather continue my ride with one functioning disc brake than one functioning rim brake, especially if hills were involved.


Each to his own though. Sure, for years we have all got along just fine and dandy on rim brakes. The best ones really are great, especially in the dry, but this does not mean that the best disc brakes aren't an improvement. Sure, some couldn't afford them, but that is life. Many couldn't justify changing because they would have to change the whole bike to accomodate them. Many will be just completely happy with what they already have and 'can't see the need', which again is fine. None of the individual justification for choices means that disc brakes aren't superior though. They simply are, period. Match them to di2 shifting (which again is just simply superior) and your riding experience is transformed. I cannot believe the difference and love it!

PP

svetty

Not sure about point 2 as the limiting factor is road-tyre adhesion. This isn't the same in the wet as dry so braking performance isn't going to be the same. Granted discs are less affected by wet than rims though....

pilot_pete

Svetty wrote:

Not sure about point 2 as the limiting factor is road-tyre adhesion. This isn't the same in the wet as dry so braking performance isn't going to be the same. Granted discs are less affected by wet than rims though....

You are of course right, it was the way I wrote it. What I meant was the performance of a disc brake is not affected adversely in the wet as opposed to the overall braking performance which obviously is due to less friction of the tyre with the road. This is in contrast to a rim brake where the brake is adversely affected as well as the overall stopping performance.

PP

neeb

I think it's important when debating this issue to always keep in mind that the performance differences of disc brakes compared to rim brakes are pretty much going to be dependent on how much you weigh. The force required to slow an object down is directy proportional to its mass (F=ma). Someone (plus bike) weighing 105kg rather than 70kg is going to need to pull the lever on a rim brake bike 50% harder to stop in the same distance and is going to notice the advantages of increased braking power much more. Modulation is an aspect of this too - the harder you have to pull the lever of a rim brake the less modulation it has. I sometimes wonder whether this whole debate could just be a misunderstanding between skinny people and bigger people.

Giraffoto

neeb wrote:

. . . I sometimes wonder whether this whole debate could just be a misunderstanding between skinny people and bigger people.

I'm going to stick with rim brakes because now it turns out that disk brakes make you look fat

thomasmorris

neeb wrote:

The force required to slow an object down is directy proportional to its mass (F=ma). Someone (plus bike) weighing 105kg rather than 70kg is going to need to pull the lever on a rim brake bike 50% harder to stop in the same distance and is going to notice the advantages of increased braking power much more.

Except they can't pull the lever 50% harder because they'd lock up a wheel... in an emergency stop, both riders will be modulating their brakes so they don't lock up, so lever force will be very similar (assuming the same tyres).

Heavier people aren't taking longer to stop because they're physically struggling to pull the levers hard enough (we're not on wet steel rims with cork pads anymore!). Heavier people take longer to stop because more energy has to go through the same contact patch. So having more powerful brakes won't allow them to stop quicker, but having a larger contact patch might.

neeb wrote:

Modulation is an aspect of this too - the harder you have to pull the lever of a rim brake the less modulation it has. I sometimes wonder whether this whole debate could just be a misunderstanding between skinny people and bigger people.

Brakes have the same level of modulation no matter how hard you pull them: modulation is independent of power.

However, the person pulling the brake may have less co-ordination if they are at the limits of their grip strength. But for the reasons above, wheels lock well before riders reach their grip strength. And even then if grip strength /power was a problem it could be easily solved through cable pull ratios.

So the decision really comes down to modulation (independent of rider weight) and rim wear (cheaper to replace discs than rims). Oh, and maybe tyre clearance.

Disc brakes better modulation comes from:
1) having a perfect braking surface to which friction can be applied consistently without contamination or bulges.
2) having hydraulic fluid in a hose which has less friction than a cable, so that the resistance the rider feels at the lever is made up more by pad-disc pressure, giving better 'feel'.
3) Hydraulic fluid compresses less than cables stretch. This gives you less sponge and thus better 'feel'.

kajjal

The increased modulation does also come from the power of the disc brakes. They are several times more powerful than rim brakes and this range of easily usable power also gives improved modulation.

Disc brakes are not about locking up wheels but having more powerful, consistent brakes with better feel that take less effort to use. GCN tested two light weight road bike riders and found in the dry discs were better but not by alot. As the road got wetter and loser the disc brakes performed increasingly better. This is why they are widespread in mountain biking, the need for powerful well modulated brakes. Going between my 105 Road bike and my road bike with hydraulic discs is a huge difference. On 105 the brakes now feel dead, under powered and i can feel the cables stretch.

thomasmorris

Kajjal wrote:

The increased modulation does also come from the power of the disc brakes. They are several times more powerful than rim brakes and this range of easily usable power also gives improved modulation.

I agree with everything you say, except the above.

Disc brakes can be made more powerful, but so can rim brakes. The most powerful brake I've used was a hydraulic rim brake. You could make rim brakes much more powerful with soft pads and bigger cable pull ratios.

Modulation does not come from power. In fact, brakes that are too powerful can be difficult to modulate as they lock up with the finest touch.

Modulation is purely from how direct lever pressure correlates with braking force. Stretchy cables (or compressing outers), friction, flexing in the brake caliper arms and inconsistent braking surface all reduce modulation. Then there is pad feel which is determined by how 'sticky' the pads are and how spongey they are.

neeb

thomasmorris wrote:

Except they can't pull the lever 50% harder because they'd lock up a wheel... in an emergency stop, both riders will be modulating their brakes so they don't lock up, so lever force will be very similar (assuming the same tyres).

Heavier people aren't taking longer to stop because they're physically struggling to pull the levers hard enough (we're not on wet steel rims with cork pads anymore!). Heavier people take longer to stop because more energy has to go through the same contact patch. So having more powerful brakes won't allow them to stop quicker, but having a larger contact patch might.

Yes of course it's the point at which the wheel locks up that determines the limit of useful braking power - but the vast majority of the braking we do is below that limit. The point I was trying to make is that for a given amount of deceleration on the same braking system, the heavier rider has to pull the lever harder. This means that rim brakes will feel proportionately less sensitive the heavier the rider is, and so the greater sensitivity of disc brakes will be a more significant subjective advantage (although the difference between rim and disc braking sensitivity will be the same for both the lighter and the heavier rider of course, this difference will be more noticeable for the heavier rider because the exertion required for rim brakes approaches more closely a level that might be perceived as less than perfectly comfortable). I'm assuming that hand strength is much the same for lighter and heaver riders of course, or at least doesn't scale directly with body weight..

thomasmorris wrote:

Brakes have the same level of modulation no matter how hard you pull them: modulation is independent of power.

However, the person pulling the brake may have less co-ordination if they are at the limits of their grip strength. But for the reasons above, wheels lock well before riders reach their grip strength. And even then if grip strength /power was a problem it could be easily solved through cable pull ratios.

So the decision really comes down to modulation (independent of rider weight) and rim wear (cheaper to replace discs than rims). Oh, and maybe tyre clearance.

Disc brakes better modulation comes from:
1) having a perfect braking surface to which friction can be applied consistently without contamination or bulges.
2) having hydraulic fluid in a hose which has less friction than a cable, so that the resistance the rider feels at the lever is made up more by pad-disc pressure, giving better 'feel'.
3) Hydraulic fluid compresses less than cables stretch. This gives you less sponge and thus better 'feel'.

I firmly believe that a major aspect of modulation is the extent to which required lever force is within the optimal range of hand muscle sensitivity. It's not just that we have less coordination at the limits of grip strength - rather we have much finer muscular control at lower applied forces. It's biomechanics as well as brake mechanics that determines modulation. There are practical limits to how much you can increase cable rim brake sensitivity by increasing lever pull ratio.

Furthermore as regards the bike-mechanical aspects of modulation, many of the advantages of discs over cable rim brakes are also relative to the force applied (and hence rider weight for a given amount of deceleration). So while it's true that hydraulic fluid compresses less than cables stretch, the difference will be more apparent the more force you are applying. Cable stretch will be more signifcant (and so the brakes more spongy feeling) for the heavier rider given the same amount of deceleration. Cable rim brakes feel like hydraulic disk brakes when you operate them very lightly (there's effectively no cable stretch), it's just that they aren't doing any stopping at that pressure..

I don't believe that cable friction is significant for perceived resistance in a well set-up modern rim brake system, for the front brake at least. It's more significant for the rear brake admittedly.

thomasmorris

I just don't think power gives better modulation. I tend to feel the opposite, more powerful brakes are harder to modulate. Executing micro movements whilst the gripping a bar tight is difficult.

If more power equalled better modulation every one would run huge discs. But they don't.

Brake modulation is about precision and feel, so maybe it's personal preference. But I'm still of the opinion that modulation is completely independent of power.

kajjal

I understand what you mean but if you tried a bike with good quality hydraulic disc brakes it would make more sense. My first proper mountain bike in the early 1990's had caliper brakes which were poor with little or no feel. My next bike had v brakes which had less pad movement and greater power, they worked well in comparison and you could feel the braking better. My current bikes have decent hydraulic disc brakes with less pad movement again but alot more power and feel. They make the vbrakes feel wooden and under powered in comparison.

thomasmorris

On my mtbs I've had cantilever, v brakes, mechanical disc and hydraulic disc.

My trials bike I've had mechanical disc, hydraulic rim and hydraulic disc.

Road I have had caliper and dual pivot caliper and mechanical disc.

On all I've had different pads, tarred rims and grinded rims.

The most powerful were hydraulic rim brakes. But I changed to discs as whilst they didn't lock as easily they were far more precise.

When I moved to discs on the mtb from v's I couldn't notice much difference in stopping power in the dry, but the power remained constant in the wet.

Downhill and trials bike have big discs with tons of power, but they also have wide super tacky tyres to match.

For everything else, once you can lock the wheels up with one finger you have ample power. Modulation is then key, and I'm in all my brake experiences I have yet to see a correlation with outright power.

cycleclinic

Imposter for that last bend in this race which was wet if i could have braked later it would have helped. I had hardly any riders around me. A couple to the right who went wide. The main bunch was behind. So before you comment and tell me i know nothing get the facts straight.

Also there is confidence in the brakes. That race i mentioned was a wet one. As i spent alot of the race at or near the front of the group either stringing it out or in the string i had to brake early for the bends as i had water to scrub from the brakes before i got bite. Even when in the bunch and braking disc brakes would have helped as i had a number of oh shit moments when someone in front braked and i pulled my levers and little happened and the water gets srubbed and i slow more suddenly. Thevreminded me get back on the front. With disc brakes i would have slowed at the rate i intended not faster than i needed and not slower. On the last lap about half way through i was trying to shut down the breakaway. There where a series of tight bends in one of the villages i had been leading the bunch for a few miles and i dont know how many seconds i lost in the villages but being able to control my braking better might have allowed me to get through the bends quicker a7nd i would not have felt the need to go as hard as did up the hill. So yes disc brakes would have helped me in that race. In fact in every race i have done i would perfer disc brakes over rim brakes. Braking is so much controlable. It does not matter if that pack has some riders on disc brakes and some on rim brakes as it would cause no issues that are not already present. It is already the case that some people brake too early for a bend, brake too much, brake too late and take the wrong line or riding slowly round it. You already have riders like me passes folk in the bends or riders like me getting passed in the bends. If disc brakes were allowed the same sitution will still exist it will be no different. There will be no more accidents because of disc brakes. They already happen because of dodgy riding and will still happen because better brakes dont improve riders skill levels.

All these arguements used against disc brakes are pretty bogus

I was riding my old trek today with campag veloce brakes. These brakes work very well for rim brakes but are on off affairs. I have record brakes, super rdvord brakes, dur ace brakes and non work properly in the wet. In the dry they o.k some modulate better than others. Non however a patch on my trp spyres and my wife r785 braking system is something else.

How quickly i can stop is limited by tyre adhesion and with rim brakes and disc brakes i can get to the limits of grip but how the brake feels is as important to me as how easy ko is to lock the wheel. The bb7 and other one piston mechanical brakes are rubbish. The spyres work much better now i have ebc pads in them. The tektro pads organic and sintered where not that great.

Modulation has nothing to do with braking power. Of course braking power is not real. The caliper applies a torque to the rim or rotor. While energy is being disapated over time this is not how the term power is used in physics. That aside shimano's xtr m985 and m9000 brakes develop enough braking torque to throw the back wheel up at will but i can modulate the brake so well this rarely happens. On road bikes it is certainly not as easy to lock the front wheel with disc brakes but this does not translate to longer stopping distances. It maybe your are able to avoid front wheel lock with disc brakes simply because of the better modulation of rim brakes. Also there is real load on my road bike with disc brakes so it will be harder to lock the front wheel anyway.

DeVlaeminck

As I say I wait for the pro peloton to have a mix of disc and rim brakes because that will soon show up if one is significantly better than the other.

cycleclinic

No one will have the edge over the other. You wont get a clear result by looking at who wins and who uses what brakes as riders vary in ability too much.

DeVlaeminck

I disagree - we know who can descend well in the pro peloton so if discs are the genuine advance that you suggest we should see that.

sloppyschleckonds

DeVlaeminck wrote:

I disagree - we know who can descend well in the pro peloton so if discs are the genuine advance that you suggest we should see that.

Don't hold your breath waiting

pilot_pete

DeVlaeminck wrote:

I disagree - we know who can descend well in the pro peloton so if discs are the genuine advance that you suggest we should see that.

Rediculous. There are far too many other factors involved in this very unscientific methodology for determining 'which is better'.

PP

DeVlaeminck

I'm not suggesting that we will get a definitive answer on one descent but clearly if there is a significant difference especially on wet technical descents we should see that - cycleclinic has said that discs would allow him to gain several places on a corner - if they really are that much better then that kind of difference should be apparent over time.

pilot_pete

At the risk of getting into a very long protracted debate regarding discs in the pro peloton on a descent, again there are far too many factors at play. The only time a rider is going to seek out the greatest advantage in the wet is if he is trying to break away, or catch a break away rider. Who is to say a rider on rim brakes will be doing the same, at the same time to get a comparison?

And then you are comparing apples and oranges because one rider may be heavier, a worse or better descender, braver, more stupid, have more to lose or to gain etc etc etc.

When you are at the edge of marginal gains you may find that a disc brakes advantages for a pro rider are diminished to the point of a rim brake being more advantageous overall on a particular race/ stage. The added weight and marginally less aerodynamic disc brake makes sod all difference to me and the far superior braking makes a huge difference.

However, to a pro for example on a flat stage on something like the Tour of Qatar these marginal disadvantages may well outweigh the braking advantage. It is not as straight forward as a lighter bike is better than a heavier bike when it comes to power to weight ratio etc. It could well be that a really mountainous route also means a disc brakes bike is not an advantage compared to a lighter rim brakes bike - proportionally you will gain more by climbing faster than you will by being able to descend faster, hence why hill climbers and grand tour winners don't weigh as much as roulers!

I guess it comes down to whether they can put together a disc braked race bike that is the same weight as its rim braked counterpart and calculate the aerodynamic cost to decide if there is a gain overall. They should be able to as all bikes need to meet the UCI minimum weight and some actually put weight on to reach that.

There simply is no need to try to ascertain whether disc brakes are better than rim by watching the pros. For everyday riders who aren't on the ragged performance edge they simply are better for the reasons I listed earlier. Period.

PP