All very good points Jack. I guess for me it's because this is a track car so the bigger the stopping power the better so I couldn't understand why you wouldn't go the biggest possible rotor. And it fits my 18 inch BBS too so why not? But as a generic BBK by AP, I'm sure 355mm will be plenty as you said and most people will not want to go so large.
Taka, the thing to bear in mind also is that the bigger the stopping power, the less time you will be on the brakes so it will actually run cooler too. I will see how we go, but may need brake ducts down the track. But I doubt it given the nature of track time we do, which is limited to small number of laps at any time.
Originally Posted by FazerBoy
I'm not quite clear on this insistence of yours regarding the 5555?
I presume they are using the 5575 and 355mm discs because they will fit behind an 18" wheel (albeit not the standard one). I presume that with larger discs you will need a 19" wheel which means larger and more expensive tyres, more mass to accelerate, possible adverse effect on handling and with a small car like the 135i perhaps 19" wheels are a little out of proportion.
But what do I know? I'm leaving it to AP and Birds to sort out - I imagine they know what they're doing.