[Closed] Brake Disc Q:

One for the keyboard engineers possibly.

Been sorting through my box of used spares and have noticed that all the old discs I have squirrelled away have worn unevenly. Hopes that have worn with a thinner groove 2/3rds the way down, or in the case of having been used with an M4 caliper having 2mm of unused surface below the wear track. Shimano discs that have worn thinner by where the arms join the main disc. The wavy Avids that seem to only be anywhere near the pads for 50% of their circumference. The only sensible design that has worn evenly I have in the pile seems to be the Avid G2 which is simple and completely round! But even that had a habit of wearing the edge of the pads first, then the middle, then the edges etc so the brake was always low on power.

Why? Surely it's not that hard to produce a brake disc that wears uniformly and doesn't create a pulse sensation when braking. I know why the grooves/holes/slits are there, to aid removal of dirt, water and to aid cooling. It's why solid discs aren't the solution (or are they?). Is it that we (as a community of bikers) insist on the discs looking 'trendy' and 'out there', hence the plethora of designs that look styled rather than engineered, or has no-one found that perfect design yet? It doesn't seem to be a problem on motorbikes which run in similar conditions, why do MTB brakes have this problem? Obsession with lightweight maybe?

Thi isn't a rant, I genuinely want to understand why as it's obviously not as simple as it seems to make a perfect disc!