Correct centering of the double action caliper on the rotor is very important, regardless of the fact that there are live pistons on both sides of the blade supposedly "self-centering" themselves. The fact is, application of the brake intrinsically tries to pull the caliper assembly out of its design plane via the not inconsiderable applied hydraulic forces. On this front, there's two significant actions taking place in the process of braking:
1. Distortion; the hydraulic forces in play not only apply themselves in pressurizing the pistons acting upon the brake pads and working towards stopping the rotational forces of the rotor/wheel assembly, but also play out in the opposite direction as well in attempting to spread the caliper halves. A phenomenon often referred to as the clamshell effect. This usually manifests itself with radially tapered (bottom to top) pad wear, brake howl and piston retraction problems due to this distortion. The new generation calipers, pioneered by Brembo and adopted by Tokico, with their individual pad-per-piston design provides for the incorporation of a rather massive central bridge across the top of the caliper minimizing if not eliminating this effect. As described, this has nothing to do with the caliper being mounted radially or in old-school trailing edge, perpendicular fashion.
Caliper Mount Location; here's where and how the caliper is mounted on the forks becomes a factor, and this is strictly focused on the occurrence of TORSIONAL caliper flex. Bear in mind and heretofore, all conventional calipers are mounted at the trailing edge of the line of force, combined with the fact the energy transfer (to the forks) of the braking forces are focused on just one side of the spinning rotor. Then factor in the normal production tolerances between the mounting faces of the rotor/wheel, fork/caliper, plus perpendicular axle alignment within the wheel to these faces, and more. Of course we can stir the pot with greater possibilities for misalignment with (even just slightly) out of true axles and fork tubes. The end result is there’s always some degree of mating issues that ultimately effect performance potential yet are still within factory tolerance. But it is predominantly the torsional twisting effect of the caliper that is the main culprit for setting the gremlins loose during hard braking. The relatively new radial mount caliper design virtually eliminates this torsion flex problem since it more efficiently spreads the load equally both fore and aft to the line of force. It also offers the additional advantage of better (quicker) release at the end of the braking sequence as an additional design benefit.
Different friction materials have their own personalities and characteristics with some leaving greater material transfer on the rotor surface than others. Ideally, when testing pads, the rotor surface should be thoroughly cleaned between compounds by either bead-blasting the rotor surface or using one of the new Rotor Hones we now stock for this purpose. This is something preached regularly to racers we sponsor to optimize braking performance and minimize excessive deposition layer build-up, which can lead to brake judder and screeching noise. Every shop should have a rotor hone in their service department...a very cool and useful tool.
"Wave" type rotors with longish slots can have interesting if not adverse reactions to the very short length 4 pad caliper designs. These pads having much reduced bearing surface area than a conventionally longer pad create greater opportunity for deflection into those slots and missing parts of the rotor. This thereby creates greater tendency towards negative reactions.
Hole Patterns: the individual brake rotor hole pattern (or sine-wave in the case of the "petal" types) all contribute to producing a distinctive sound. Again some patterns produce more than others. Of course friction material plays a part as well with the sintered metal category usually the noisiest in large part due to their greater density and higher metal content. Our rotors and hole patterns are designed to continually clean the face of the friction material evenly across the radius.
Final note on noise; if not properly assembled, the front wheel can actually bind up in the forks causing alignment issues and excessive brake drag (not to mention much greater fork stiction related problems). Any experienced mechanic should be aware of the proper wheel assembly/installment procedures to avoid this phenomenon.
There's actually another significant factor to add as well; brake pad backplate distortion. If the backplate warps, an occurrence much more common with the longer six pot pads than with the short individual pad per piston model for obvious reasons, major problems will result. Brake drag, over-heating, glazing of friction material, excessive noise, warped rotors, etc. are just some of the anticipated consequences.