15 years as a brake engineer, including two BMW related projects (cars) here. The reason the callipers stick and misbehave is down to the priorities of the vehicle manufacturers and hence the materials:
1. Must meet minimum legal performance ; can't sell without it.
2. Must feel safe to some ****ed up MCN employee who's got to ride it at least a mile to qualify for the next all expenses paid junket to Spain or Bali.
=3. Must be cheaper to buy than the last one.
=3. Must meet the latest showroom trends, so no rust, radial mounting, lots of slots and holes
4. (New Entry) must be good enough not to result in internet chatroom damnation, but needn't be so good as to stop the manufacturer selling a £500, nineteen calliper floating tripple disk upgrade.
5. Must eat pads at a rate sufficient to satisfy the aftermarkets sales target.
6. 80% of the first production run should still be MOT passes when the model goes out of production (rebuilds allowed).
They don't care less about 5 year old bikes.
BMW have a bigger problem. You get a job there because Uncle Herman had a job there. You go into the brakes section because old Werner retired a week after you started. You work there for 50 years and never talk to anyone outside the brakes team, especially sales. You change as little as possible. When some bloke in a suit tells you stainless is required you say "Zis is not possible, cast iron is best" because that's what old Werner told you to say. When the suit says stainless is required or the company will go bust again you are shocked and ask why. To prevent the corrosion that will cause the destruction of the company, you do not pick the barely rust proof cast monkey metal Yamaha chose, you pick medical grade 316. This has the braking properties of a greased apfel strudel, but at least the company did not go bust again.
A brake engineer would pick plain cast iron and the callipers would be smaller as a result. Marketing would hate it. The brakes on our bikes are the equivalent of Primark copies of red Gucci Stilletoes not the army boots we really want.
Andy
