Disk brake teething troubles.

I've built up a spare set of wheels for off-road use that I can throw on for next weekend's cyclocross enduro event.

I made sure that the hubs were the same size, the disks were the same size, and thought I'd be clever by choosing fully floating disks.

Except the stud which attaches the disk to the rotor fouls the bottom edge of the brake calliper body.

Hmm.. Time to get the dremel out. I can see from the scratch marks where it's rubbing and it's certainly not going to affect the strength of the caliper, but it's an interesting development considering they should all be compatible.

Well.. after a VERY patient hour or so with a file, it fits beautifully, and it just needs a slight tweak of the pad adjusters when I swap wheels.

oh but it's coming..

SRAMare doing a Hydraulic disk-brake next year in their RED groupset.
Shimano have cable-operated on the way.

Hydraulics are marginally lighter
More control/modulation of braking control.
Potential for lighter rims and for the mass to be centralised on the hub reducing the moment of inertial making it easier to accelerate the wheel.
Damage to the rim doesn't affect the braking surface
The braking surface is raised up, away from the surface of the road minimising contamination and helping stop it getting wet so improving braking in the wet.
Carbon rims can be used with more confidence as the poor heat dissipation properties of carbon are no longer an issue.
Wheel changes can be quicker and potentially safer as you don't need to let air out the tyre to get it past the brake blocks, or equally, you don't have to worry about forgetting to flip the calliper 'switch' which allows the wheel to come out easily.

And while some argue that disk-brakes require heavier/more spokes or a 4-cross spoke pattern, take a look at the Crank Brothers Iodine or Cobalt 29" wheels.

alec wrote:

I disagree - I think it's marketing hype, it's not going to happen any time soon, and certainly not on my bike.

feef wrote:

Hydraulics are marginally lighter

Not as I understand it - disk brakes, whether hydraulic or mechanical will be heavier by 150g to 500g for the complete bike according to Magura

Magura are wrong for hydraulic systems. Cable operated, yes. Note, also, Magura are launching a hydraulic calliper for next year.

alec wrote:

Potential for lighter rims and for the mass to be centralised on the hub reducing the moment of inertial making it easier to accelerate the wheel.

I think it's extremely unlikely that rims can be made lighter even if they are not doing braking duty. The disk will be an additional rotating weight.

[/quote]
If it's true that rims cannot be made lighter, as the disk is at the center, it's impact on rotational inertia, if any, will be negligible.

alec wrote:

Damage to the rim doesn't affect the braking surface

Not a problem that I have ever encountered.

But not something you can say you will never encounter.

alec wrote:

The braking surface is raised up, away from the surface of the road minimising contamination and helping stop it getting wet so improving braking in the wet.

Current caliper systems, whether on aluminium or carbon rims will lock up in the wet. What more do we need?

alec wrote:

Carbon rims can be used with more confidence as the poor heat dissipation properties of carbon are no longer an issue.

Heat dissipation on the disc is also a major concern to the extent that people are worried about the fluid boiling in hydraulic systems

An unfounded worry. If it was the case, we'd have huge problems in the MTB community already.

alec wrote:

Wheel changes can be quicker and potentially safer as you don't need to let air out the tyre to get it past the brake blocks, or equally, you don't have to worry about forgetting to flip the calliper 'switch' which allows the wheel to come out easily.

Experienced roadies and particularly pros don't have a problem with this - flip the switch on the calipers or on the levers - it's second nature - have you seen the speed of wheel change in a race? With a disc wheel, don't you need to feed the rotor into the brake shoes at the same time as fitting the cassette into the chain and the hub into the dropouts? And what happens when the levers get pulled by mistake without the rotor in place?

Nothing.. the pads retract back. No problems there. As for 'feeding the rotor in' I just drop mine in.. I don't even look at the calliper when fitting and concentrate one the cassette.. it just fits.

alec wrote:

And while some argue that disk-brakes require heavier/more spokes or a 4-cross spoke pattern, take a look at the Crank Brothers Iodine or Cobalt 29" wheels.

Well they obviously do require more robust spoking because they have to sustain torque between the hub and the rim that is not present with rim braking.

But modern technology and materials means that you can get suitable strength without a significant increase in weight. Rear wheels, for example, already have to withstand significant torques from the drive from he rider. The braking forces aren't significantly higher, especially as the disk is often of a larger radius than the highest gear.

alec wrote:

More disadvantages of disks:

Dished front wheel
Braking force creates a torque between the hub and the rim/tyre: more robust spoking must be required
Frame elements need to take the braking force at the ends of the stays and forks - therefore more robust stays and forks required
Transition impossibly complex - which team will be first in the peloton to have disk brakes and not be able to use neutral service?

Dished front wheel : if the wheel is strong enough, why is dishing a problem?

Braking torques: again,not an issue. In MTB, they have suspension forks which would show up torsional problems far sooner than in rigid forks. In my own experience, I've not seen the forks twist at all either.


Frame design : Look at my frame. It has one alloy reinforcing tube less than 10cm long in the rear triangle, and the carbon forks are more than strong enough. As technology and materials progress it will certainly not be an issue.

As for the 'neutral' maintenance in the peloton.. Worst case would be disk-compatible hubs with braked rims on, but only having a couple of wheels with the brake rotors already fitted.

alec wrote:

I've never had to take a file to my calipers

ahh this is the problem of being at the cutting edge
In hind-sight, if I'd got a different model of disk, it wouldn't have been an issue. Part of the problem is that I'm having to use some MTB components as there just isn't the choice out there for road bikes just yet.


fwiw, almost all of the concerns you raise are pretty much identical to the concerns raised in the MTB community some years ago. Now disks are pretty much the standard in MTB without any of the concerns coming true.

Colnago seem to agree with me:
www.colnago.com/disc-braking/

Quote central!

The pro peloton are the early adopters of breaking technology, we have see this time and time again with wheelset prototypes, electronic shifting, materials used in frames etc etc. The fact is that we have not seen any disc breaks in the peloton yet goes to show we are not any closer of going down that route.

Imagine the investment that it would take? Service cars, frame changes, wheel changes. I suspect for the gain seen they will not bother for some time yet.

For the consumer market then yes, I think that it could be a rare example of this market adopting (in a minority) before the pro's do.

Lets face it, for most of us that means a complete new bike without exception to benefit from disc brakes. That is, without question the major issue.

Oh and by the way, Magura are already supplying hydraulic RIM brakes to the pro tour bikes
www.magura.com/en/roadbike/home.html (factory supplied with cervelo P5)

We will see hydraulic rim brakes well before disc brakes in my view

and this will only be on TT specific bikes until they can integrate the magura's into shifting hood/brake combos.

Quite interesting design but look at the extra gubbins needed:
www.bikeradar.com/road/gallery/article/m...m-first-ride-33781/8

You have to ask the question, is it really worth it? - even for the magura rim brakes