Hi all
Late to the party on this one, pretty busy of late with very limited time to look at what appears on the Google Alerts ...
A few accumulated points worth talking about though ...
Noise from discs, esp in the wet -
Yes, it happens. However, many of the things that are commonly blamed for it and many of the fixes are more about folklore than they are about good engineering practice.
The basic cause is the same as squeal on road brakes - the fact that a disc passing between two pads is grabbed, released, grabbed, released in a cyclic fashion, which can lead to resonance and squeal. This tendency is increased with less pad contact area and the amount that the noise gets damped by the pads is likewise related to contact area amongst other things.
What you hear is resonance of the disc / wheel system as a whole, so there are internal causes of that noise around pad type, contact and so on, and external ones including disc to wheel fitting and spoke tension.
In the wet, reduced disc / pad friction changes the resonance characteritics of the system so a system that is silent or near-silent in the dry can scream in the wet, though instances of the reverse are very rare (since a wet system rapidly dries with rotor and pad heating).
Working from basics then - the Bora One Disc compatible wheels should not promote braking noise as the spoke tensions are very high (130-150 kgs on the front brake side, approx the same on the rear gear side) and so long as the rotors are fully locked down to the correct torque (and the Campag locking rings are used so that there is correct engagement with wheel and rotor), those areas of concern are pretty much taken care of. AFS / Centrelock, by the way, was selected in part because it apperas less prone to noise than 6 bolt, the locking ring pretty much by definition applying equal pressure all the way around it's circumference, where 6-bolt struggles to do that so easily.
Facing - this is about two things - first, the mounting area needs to be faced so that as much of the caliper as possible is in tight contact with the frame (that's about thermal dumping into the frame and again, controlling resonance) and so that the caliper is perpendicular to the axle - a file can't really do that for you, unless it's wielded by a master craftsman - and even then, a disc facing tool like the Park one (which TBH has it's limitations) will still do a better job as it uses the bolt-through axle as it's mounting point, to assure a properly perpendiclar mount surface.
In just the same way as a rim brake can squeal if the pads are not held against the rim square under braking, a disc brake needs the pads to be flat to the rotor and for both to hit the rotor at the same time, and with as close to the same force as can be arranged - that means accurate facing and accurate caliper setting (and a flat rotor, of course ...)
The Campag pads have a coating on the back of the pad where it interfaces against the piston - using anything additional in this area may compromise that coating or render it to some extent ineffective - but it has two jobs - one is to damp vibration and so resonance, the second is to help reduce heat transfer from rotor via the pad to the piston and thereby the caliper / fluid. That coating was responsible for a hefty part of the two year wait that the market had for the Campag system after early trial versions were spotted in the peloton - so I'd advise against doing anything that might compromise it - we know it works, we tested it in real-world situations as well as the lab for what seemed like forever-and-a-day!
Assuming that the pads / caliper set up is dead right and that the through axles are tight (and it is worth torquing them as different through-axle tightnesses can sometimes change the exact caliper to rotor position), you should have a very close to silent system in the dry. This was genuinely one of the major design objectives, set by Mr Campagnolo himself eight years ago when the disc project first started ... hence the time spent on the backing compound on the pads for instance. Keeping the pads and rotors clean from day to day (obviously you can't go cleaning them mid-ride ... or maybe ...
) will help to reduce wet weather noise but to eliminate it is the pot of gold at the rainbow's end ...
Once the pads are bedded, wet weather noise can also be reduced (but not eliminated) by glaze removal with a flat metalworking file that doesn't get used for anything else (thereby avoiding any possible contamination) and thoroughly cleaning the rotors with IPA. Both glaze and surface deposits on the rotors make pad to rotor "slippage" worse so not only does the glazing and surface deposition increase but it also can (depending on exact resonant frequencies) make noise worse as it changes the frequency at which the grab-release cycle occurs ...
Adjustment - lever reach and bite point are independant of each other and bite point adjustment does not change pad-to-rotor spacing or pad rollback. Fill / bleed the system with the bite point set to "short" and we advise the reach adjusters on both levers are set as long as possible, so as to make it easier to dial in the same feel on both brakes after filling / bleeding operations.
Chainline - the differences on the H11 and HO cranksets are changed ring spacing (opened out by 0.8mm) to reduce the chain clatter on the back of the big ring when running small-small gear combos, revised shaping of the back of the big chainring (to assist up- and down-shift with the wider spacing) and new tooth profiles so that entry and exit angles from the chainrings can be wider - hence the inter-compatibility of H11 and HO chainsets (and now 12v too) with disc and rim systems. The chainline is managed on the rings to place it 1mm further out (44.5mm +/-0.5mm rather than 43mm (same tolerances) so providing a compromise between the ideal for 130mm rim and the ideal for 135mm disc rear spacings. The shift outward in the chainline is almost in the middle of the 2.5mm differential that would be needed for total disc compatibility had the rings not been changed and the compromise works better for big rig cross-chaining, where there is a greater tendency for the chain to be pulled off the big chainring towards the inside by chain tension.
Bolt-through - yes, it's a PITA but it keeps the parts of the system better aligned in both set-up terms (esp if a torque wrench is used to tighten the bolt-through axles) as well as increasing the overall rigidity of the wheel / fork or wheel / rear end system.
It is a different braking technique with discs to get the most out of them but as others have noted, in abolute terms it's about the rubber-to-road junction, where effectiveness of a braking system is really governed. And that doesn't change, rim or disc. However, discs do allow drag braking on carbon rims (not recommended with rim brake!) and the same braking force applied at the tyre / tarmac interface is generally gained at lower effort levels at the lever, so there is an increase in accuracy. However, most users don't get anywhere near the limits where the very fine modulation that this allows is really of importance. To some extent rims can also be made lighter (although there is a trade-off in increased spoke counts and in the hub) so peripheral spinning weight, where it has most effect on handling (due to rotational inertia) can be reduced.
HTH
A Tech-Reps work is never done ...
Head Tech, Campagnolo main UK ASC
Pls contact via velotechcycling"at"aim"dot"com, not PM, for a quicker answer. Thanks!