Learned something new today. The instructions for the Spiegler Rotors I bolted onto the K bike talk about "lining up the wave pattern" between the rotors. I thought, maybe, they were talking about the wave pattern in the holes drilled into the disk.

It turns out there are "wave rotors":



So that line up procedure does not apply to the circular rotors that I have.

Wow dude.

By the way, the wow dude was for the "it turns out there are wave rotors". Um, I've got wave rotors on my mountain bike that I got 5 years ago and I'm by no means a trend setter.

Yermo needs to get out more.

Interestingly I just got a contrarian reply on the list, which matches basically what I was thinking ....

Subject: Re: [BMWTech] A Question about "Rotor Alignment".


Ah. Ok. I guess it's a case of "one set of instructions to rule them all".

For the life of me I couldn't think of a reason why the pattern of holes
alignment would make any difference at all. This certainly clears up the
confusion.

Thanks!
****************
I do not agree.

When you bolt the assembly onto the bike, just have the rotor holes in line with each other, left-right.
The first photo did show the drilling differences; don't let 'wave' disturb your thinking...there IS a wave effect caused by the drilling...LOOK at the drilling pattern!
I think, not sure, not having tested those drilled rotors, that it is not any big deal.... but having things the same on both sides (obviously the brakes are opposite each other physically on bikes so the calipers are not a problem) theoretically reduces any tendency towards shuddering by making braking more even, side to side; and, limits pulsing and noise. Things could get more interesting if the discs holes (or waves on those that are obviously cut that way) were not in line with each other, say way different, and you had UNequal piston sizes in your calipers. That is VERY COMMON theses days. You would then have different biting, left-right, and I'd actually expect shuddering and other things to happen.
Symmetry is almost always the best route with mechanical things under stress, especially if paired.
Think about how the braking on any one disc will be in regards to the other disc, at any short period of time as the wheel rotates maybe 30 to 60 degrees or so., first one braking side grips more than the other side of the wheel, then it cyclically reverses. Granted that the discs are not separated too far, but there is still a twisting moment....that can cause left-right shuddering, maybe even a wobble.
This is the same type of reason that some dual-disc bikes with one slightly warped disc, is not stable in braking.
It happens on a single disc too, sometimes from a hardened place on the disc, sometimes from a warped disc. Pulsing in the brakes.

Snowbum

I'm gonna have to go ahead and call "BS" on this one. Given the other factors affecting the forces on the two rotors, other than for maybe the first five minutes after you drive it out of the showroom, the "stopping forces" on each side will always differ.

Think machining differences in the calipers, tolerance ranges (I have measured my rotors and they are NOT even close to being the same thickness), corrosion, metallurgy variances, hell, the alignment of the planets, whatever...never going to have the same forces on both sides of the wheel.

And besides, some bikes only have one caliper to start with. How is that not completely unstable?

Just looked at my rotors, they are most definitely NOT aligned WRT the drilled holes. In addition, my bike has linked brakes so there are 4 pads working the left rotor and only 2 working the right one. The other two on the right are operated by the back brake foot pedal under panic stops...which is rare. Thus I think the forces are totally unequal and I've certainly had no problems.

Put the damn holes where ever you want. I've ridden with you and I've never even seen you use your brakes!

I don't have any experience with these rotors, but consider that even if you have a single rotor on one side of the wheel or two rotors of different thickness, they are smooth rotors. So once the pistons push the pads against the rotors they begin to grab and it is a steady application of friction. The fact that two rotors may have different thickness is not important, because the pistons will adjust to them and still apply evenly.

Wave rotors, though, by design cause pulses in the system by constantly catching a new leading edge. It's plausible that such pulsing happening on both sides at the same time, but not synchronously, could cause a noticable shudder.

But like I said, I haven't used them.

Edit: Yermo, were you having problems with the new rotors?

I suppose I could see your point with wave rotors but with regular drilled rotors where the holes are should not make any difference.

I thought the advantage was not so much catching a new edge, but cooling/additional surface area and lower weight. talks about their flatness and heat dissipation, not edges.

The article Yermo linked to above mentions both better feel from leading edges of the wave pattern as well as better heat dissipation.