disc brakes in cyclocross at last

[Smokin Joe]

Well if you're in the road environment that the UCI regulate:

The brake fade 'cos a disc can't disperse the heat generated in an alpine descent.

The overweight forks that are required to use them.

The issues with compatibility and quick wheel changes.


When these get sorted out then the manufacturers and riders will pressurise the UCI to change (like in cyclo cross).

Brake fade in the heat? Have you ever seen a 150 kilo GP motorcycle nearly stand on it's nose as the rider brakes from 220mph down to 40 when the track temperature is 40c +?

Forks would not need to be "overweight". Bikes already have to have weight added to come up to the UCI minimum.

Having discs would only marginally slow wheel changes if at all as the wheel just drops straight out. Compatibility doesn't cause problems with different teams using Campag/Shimano/10/11 speed now.

 

[MartinC]

Brake fade in the heat? Have you ever seen a 150 kilo GP motorcycle nearly stand on it's nose as the rider brakes from 220mph down to 40 when the track temperature is 40c +?

Forks would not need to be "overweight". Bikes already have to have weight added to come up to the UCI minimum.

Having discs would only marginally slow wheel changes if at all as the wheel just drops straight out. Compatibility doesn't cause problems with different teams using Campag/Shimano/10/11 speed now.

We're talking about the braking heat generated on a long descent on a lightweight bicycle disk. I've never used disk brakes in these circumstance so I'm only going on what others have reported. I'm not sure that the analogy you quote is too relevant. It may be that future disc brakes could be developed to overcome this within the acceptable weight parameters.

Forks for disc brake have to be stronger (i.e. heavier) than forks for rim brakes. Manufacturers still compete to make their own components lighter even though complete bikes can get past the UCI limit relatively easily now.

Any wheel from a neutral service car will go in any bike (at the cost of of a poor gearchange if it's a C/S mismatch). Adding potential rotor spec differences makes this far more problematic and wheel changes slower.

The point I and others make is that there's already a simple, effective and light braking solution in place (unlike cyclocross) so there isn't a problem to solve. Any new solution has to offer significant advantage for it to be taken up - and discs don't do this yet. The bottom line is that manufacturers and the pro peleton can't be bothered with them yet, it's only an issue for forum posters.



edit for typo

 

[andrew_s]

Overheating on alpine descents is a problem mainly experienced by the slow descender.
A plummet and stop braking style gets rid of most of the energy on air resistance. If you go down slowly it all goes into the brakes.

Overheating is just as much of a problem with rim brakes - tyres blow off, tub glue softens and the tyre rolls off the rim (just ask Joseba Beloki).

 

[zigzag]

here is an interesting read how this type of setup could solve overheating issue. i am currently looking for road bike carbon forks for disc brakes, but they don't seem to exist (at least no one sells them separately).

 

[MartinC]

Overheating on alpine descents is a problem mainly experienced by the slow descender.
A plummet and stop braking style gets rid of most of the energy on air resistance. If you go down slowly it all goes into the brakes.

Overheating is just as much of a problem with rim brakes - tyres blow off, tub glue softens and the tyre rolls off the rim (just ask Joseba Beloki).

Yes - brake hard and then let it run is definitely the best technique. Air resistance won't slow you quickly but the intermittent braking gives the rims time cool. Normally a tub with hard rim cement that's properly set will survive - I'm not sure what caused Beloki's problem. Clinchers v. tubs could be a whole new debate!

It would be interesting to see some real world data on heat dissipation. I stiil think the real bar is that rim brakes work well enough and no-one wants the harsh ride from forks beefed up to handle hub braking. Unless disc brakes offer a competitive advantage there's no motivation to use them.

 

[Smokin Joe]

I stiil think the real bar is that rim brakes work well enough and no-one wants the harsh ride from forks beefed up to handle hub braking. Unless disc brakes offer a competitive advantage there's no motivation to use them.

Beefed up forks would not give a harsher ride, quite the opposite in fact. Thin walled tubing transmits more vibration through to the rider because there is less material to absorb it.

 

[MartinC]

Beefed up forks would not give a harsher ride, quite the opposite in fact. Thin walled tubing transmits more vibration through to the rider because there is less material to absorb it.

Ah, but forks that handle the braking torque at the hub have to be less compliant than forks that don't.

 

[Dave5N]

Beloki crashed, IIRCC, when he hit a patch of molten tar.

 

[oldroadman]

Motorcycle discs fade on descents - I know from experience. They are thick, ventilated, ABS'd and large diameter, and can still fade. The hard application/run and cool technique can mitigate this, but eventually you brake hard after a series of corners and they start to fast very quickly. So sorry, I cannot see how a small lightweight and relatively thin disc will work when descending at 80/90 kph and braking on long (6/7 km +) descents. Whereas rim brakes dissipate heat and work fine. The tub glue argument is spurious, in the old days it sometimes happened, but with a correctly applied tub/glue it won't.
This is a classic case of "it ain't broke, why fix it". For MTB and cross, with mud at the tyre, tere can be seen to be a reason, but not on the road. It's simply a marketing ploy - a bit like Mr Bell decided they could sell hardshell helmet by making cycling sound much more hazardous then it actually is - but don't get me started on that one....

 

[Mr Celine]

This is a classic case of "it ain't broke, why fix it".

Perhaps because some people think it is broke. Having switched this year from a flat bar Spesh Sirrus with v brakes to a Spesh Roubaix with dual pivots I have to say that in my experience dual pivots are rubbish in comparison to v brakes. However, that's my personal opinion based on the conditions in which I ride, which do not involve alpine descents but do sometimes involve having to stop or slow down suddenly, which I for one simply can't manage on dual pivots. So bring on discs (or even just v brakes for road levers).

 

[MartinC]

Perhaps because some people think it is broke. Having switched this year from a flat bar Spesh Sirrus with v brakes to a Spesh Roubaix with dual pivots I have to say that in my experience dual pivots are rubbish in comparison to v brakes. However, that's my personal opinion based on the conditions in which I ride, which do not involve alpine descents but do sometimes involve having to stop or slow down suddenly, which I for one simply can't manage on dual pivots. So bring on discs (or even just v brakes for road levers).

Maybe. Your conclusions seem to be based on a small sample though. If you have trouble stopping or slowing down with dp's then they aren't good ones. There are differences. I've replaced unbranded dp's on bikes and seen enormous improvements - there are some bad ones out there. I've had to ease off the brake lever to stop an endo with dp's in an emergency stop.

I don't think anyone's saying that in general dp's are more powerful then discs. What they are sauing is that good dp's offer enough braking power for a road bike and that there are significant downsides to discs.

 

[Smokin Joe]

I wouldn't agree that dp's offer good enough performance already, there is room for considerable improvement. The only drawback I have heard of with discs is the supposed overheating problem which any half decent designer could engineer out, as has been done on cars and motorcycles. Remember the vehicles in race support convoys are keeping pace with the riders on Alpine descents with considerably more weight to stop and they manage ok.

It'll come and we'll all be on them in the not too distant (along with electronic shifters).

 

[MartinC]

I wouldn't agree that dp's offer good enough performance already, there is room for considerable improvement. The only drawback I have heard of with discs is the supposed overheating problem which any half decent designer could engineer out, as has been done on cars and motorcycles. Remember the vehicles in race support convoys are keeping pace with the riders on Alpine descents with considerably more weight to stop and they manage ok.

It'll come and we'll all be on them in the not too distant (along with electronic shifters).

I think we'll just have to agree to differ on this 'cos I can't see any of your points.

Dp's already supply enough braking power - that's why they've reverted to singles on the back. If you can lock the wheel then more power at the brake is irrelevant. I'm not sure what performance improvement you're looking for, the limiting factor is tyre adhesion already

You can engineer in more heat dissipation by giving the disk a bigger diameter, that's good 'cos there's already two 622mm discs on the bike already, you could use them. But how do you engineer in the extra torque resistance at the fork blade without making it less compliant and heavier. How do you engineer in aerodynamics? Cars often have trouble following the bikes down mountains and sometimes burn their brakes out - they don't manage OK. Performance motorbikes and cars have massive discs.

I can see the point of discs on an MTB with muddy rims, front suspension and fat tyres. I can see the point too in cross where the mud clearance issue makes you use either V's compromised by the STI/Ergo levers or low profile cantis with low mechanical advantage. Offering disc brakes on a good road bike is offering more weight, less comfort, less aerodynamics and brake fade in exchange for no extra braking function.

 

[oldroadman]

I think we'll just have to agree to differ on this 'cos I can't see any of your points.

Dp's already supply enough braking power - that's why they've reverted to singles on the back. If you can lock the wheel then more power at the brake is irrelevant. I'm not sure what performance improvement you're looking for, the limiting factor is tyre adhesion already

You can engineer in more heat dissipation by giving the disk a bigger diameter, that's good 'cos there's already two 622mm discs on the bike already, you could use them. But how do you engineer in the extra torque resistance at the fork blade without making it less compliant and heavier. How do you engineer in aerodynamics? Cars often have trouble following the bikes down mountains and sometimes burn their brakes out - they don't manage OK. Performance motorbikes and cars have massive discs.

I can see the point of discs on an MTB with muddy rims, front suspension and fat tyres. I can see the point too in cross where the mud clearance issue makes you use either V's compromised by the STI/Ergo levers or low profile cantis with low mechanical advantage. Offering disc brakes on a good road bike is offering more weight, less comfort, less aerodynamics and brake fade in exchange for no extra braking function.

As anyone who has raced where mountain descents are a regular feature will confirm, it's useless being able to lock wheels up, modulated braking is what's needed, and top class DR brakes can do all of that.
Correct that some cars and motos do have brake fade in the mountains, and that with big ventilated discs and six pad calipers. Again a limiting factor is tyre adhesion, which is MUCH HIGHER than on a tub or race HP. believe me, brake fade on a TV/press moto with a 90kg cameraman and all his kit, plus a 250kg moto and rider, is the cause of considerable thought when approaching a hairpin!

 

[DrSquirrel]

MTB / Cyclocross = use brakes a lot

Road = use brakes rarely


Think how often you actually use your brakes? If its really about having the most power(heat dispiation or whatnot) regardless of how often you use it, why don't you lot have more than two brakes like you would if you were on a tandem etc etc...