We've just done a couple of track days in the new JCW, one using the stock pads and one using EBC Yellowstuff. Now I notice that both sets of pads are wedge shaped. See picture below.

One side seems to be worse than the other, but I couldn't say if its only happening on one side (I wasn't keeping track of the pads by side). On one pad (pictured below) one end of the pad is 3.5mm thicker than the other. I don't know if its worse on the inside/outside or not.

What causes this? Is it a problem?

I'd guess that one piston is pushing harder than another, the calipers are the Brembo 4 pot versions, so each pad has 2 pistons each.

 

My guess (just a guess) is the retaining clips are not in place correctly allowing the pad do move. That would allow the pad to move forward under braking and may cause the pad shape.
Just something to check.

 

I'm pretty sure its not the clip, the pads seem to move easily.

After asking around it seems that this is a known problem with high performance brakes. The leading edge of the pad gets more worn for reasons I've not quite worked out. The cure for this is differential bore calipers. A concept I was previously unaware of. The differential bore means that one of the pistons in the caliper is bigger than the other, so it pushes against the pad harder. I don't know if the Brembos are differential bore, but I got the impression the pistons were the same size. I'll have to look at that next time I'm changing pads.

It seems the inside pad will wear faster (also for reasons I can't work out). So you should always visually inspect both pads, and not just rely on the pad gauge. A friend with a Ferrari says he killed a set of rotors by not checking on this. His car has 6 piston differential bore calipers.

Now I know about this issue, I'm going to have to keep an eye on it. I'll be keeping track of where the pads are, and probably rotating them so the thicker end is up.

 

I have seen other reports of this but only on track cars equipped with the electronic limited slip which applies the brakes to prevent wheel spin under acceleration. It could be that others do it as well but the additional braking makes the wear more apparent.

 

Most brembos i've seen are differentially bored, even the OEM ones on EVOs and STIs. I'd be surprised if they weren't for the Mini but that does look like the issue here. Have a look.

- drew