So I'm posting this from Honda Trailbike Forums. Thought I'd get some input from here.
I replaced my front disc (OEM), with a custom wave disc on my RD03 a couple months back. After replacing the disc and the pads, I started getting squealing from the front end, typical of a set of pads that needed to be replaced (even though I just replaced them.) After a week of thinking that maybe since I'm pretty much at the maximum material condition (new pads + new disc need to wear on each other a bit before running smoothly), I went down and took off the front wheel. What I found was that my freaking disc had eaten away at the caliper. There is a good 1.5mm shaved off. See pictures:
That whole slightly lighter gray area above brake pads is the wear area. As you can see, the disc has taken off a significant amount. It should be noted that the disc itself is hardly damaged. Probably since it is much newer and is much harder than the caliper material.
Not a great picture, but just to be thorough...
What I was noticing, as well, was that when I'm coasting to a stop, or using the back brake only, I hear no squealing whatsoever. However, when I start to apply the front brakes, I get the noise. This makes me think that when brakes are not being applied, the disc is running through the caliper with no contact, since it has eaten away at the caliper already and there is no more material to grind against. However, my caliper must be misaligned or something, since, when I apply the brakes, the disc comes in contact with the the caliper.
Then, I went back to my old disc and had a big WTF moment. My old disc is not planar... not flat. It looks like the actual friction surface (where brake pads contact) sits a few mm offset from the mounting hole surface. This has the effect of moving the brake pad surface a few mm away from the caliper (where my disc has been eaten away).
Here is the OEM disc. Looks flat and normal from this angle.... but...
There is a clearly a height difference between the inner diameter and the outer diameter. The height is relatively constant around the whole perimeter.
So my question is, is the OEM disc meant to be that way? I can't imagine my caliper has warped it into that shape... but it looks so uniformly offset... I have had one guy tell me that these are meant to be this way, and another guy swear that RD03 front discs should be flat and it looks like mine has dished from overheating... Which one is it?