I'm going to throw some gasoline on the fire. As I said in an earlier post, I am skeptical of the claims made for wave rotors. It was my suspicion, based on schooling many years ago, that the reduction in weight for a wave rotor when compared to a standard disc shaped rotor is negligible when you look at the entire front wheel/tire/caliper/lower fork assembly. And that means that any reduction in rotational inertia and/or unsprung weight will have a very very small change in handling. And, based on my observations of other riders in the 3 mc clubs I hang out with, few if any of them would or could notice any difference changing the rotor. Cleaning efficacy? I don't ride in mud and gnarly off road conditions, however, over thousands of miles, I have never seen an oily film on my rotors unless either the forks or calipers were leaking. Asphalt and gravel roads around here are, at worst, dusty or wet w/ rain water, and that dirt seems to get cleaned off by the normal operation of the caliper. Plus, I clean my calipers and slide pins whenever I service the brake pads/brake fluid. (Been doing that on my cars and bikes for over 35 years).
Anyway, I asked a friend who is an engineering prof at a university for his thoughts on this. He is a bike rider and has been for ages. The 'Q's' are my questions, the 'A's' are his answers:
I have very limited knowledge of these wave rotors but here is my take in Q&A format:
Q: Am I correct that the drop in rotating mass of a petal brake rotor compared to a traditional rotor is negligible?
A: My guess is that the difference in weight - and therefore rotating moment of inertia which affects the resistance to changing direction - is negligible and I doubt that a street rider could tell the difference. A racer might, but I’m sure that I couldn’t.
Q: If slots clean out the dirt in rotors on off road bikes, why bother with the wave pattern? Why not simply use slots?
A: it could be that some types of debris / water etc. are more effectively cleared off with the wave shape - but I don’t know for sure.
Q: Would not slots have the same effect at reducing mass (if this were an issue) and allow better braking? Obviously, no metal seen by the pad (valley of wave or slot) means no braking by the pad, but we are talking off road bikes where you don't want aggressive brakes.
A: There are two aspects to mass reduction:
the amount of material removed or eliminated by the modified geometry of the wave / slotted rotor and,
the distance from the centre of rotation of the remaining parts of the rotor.
The further away from the centreline of the rotor, the bigger the effect of changing the mass on the moment of inertia (the resistance to changing orientation (such as in turning). However, if you only consider the unsprung mass of the rotor from the standpoint of the front fork suspension, then the geometry of modifying the weight of the rotors doesn’t matter at all.
As for the difference between slots and the wave shape - I doubt there is a big difference from the standpoint of mass reduction.
For the vast majority of street riders, these rotors are largely a styling exercise IMO. We don’t use anything like the capability built into modern street bikes, but they sure look cool!