Crap - this moved on a lot!
Erm, in brief:
Brake bias, I don't know anyone who knows how to change it via the ECU, so I'll chose the physical method instead... that's not poo-pooing your idea - just makes more sense to me.
You cant actually 'adjust' the bias in the ECU. But what it does do is basically re-define the default bias, depending on what physical hardware is at each end. So if we just stick with the same size rear anchors, and look at differing front anchors - then a 312mm disc will provide more effective braking effort for the same pedal pressure as a 286mm, and a 345mm disc will be more than the 312 and the 286. But because the bias is actually controlled electronically, rather than by old skool pressure limiting valves or load sensing valves - then any 'change' to disc performance at one end, which isn't matched by a (proportionately) equal change at the other - well this can seriously upset the bias - or brake balance.
Detail here:
http://wiki.ross-tech.com/index.php/VW_Golf_%281K%29_Brake_Electronics_%28MK60%29R32 rears go on ok, although the splash guard will only locate to 2 holes instead of 3. I haven't done the mod myself, so until I do then that isn't gospel... but seemingly plenty of others have.
As in - R32 rear calipers, discs, etc - or just the discs?
RS4 fronts are going on, it's being done by AMD and others - I have no idea what's involved to say if it's a simple or chisel & hammer job??
The caliper mounts will be quite different, as will the disc 'bells' - so some 're-engineering' will be required. I take it you arn't going for the Ceramics off the RS4?
Not sure what you mean on the caliper piston size point - the APs are 6-pots and the R32's are twin, so I wouldn't necessarily expect the same sizes, don't 6/8-pots usually have staggered size pistons for "feel" and even pad wear??
I'm referring to the actual diameter of the piston in the caliper, and specifically for the rears - and this is all relevent to the hydraulic advantages formulae. The dia of the R32 rear piston is 41mm, whereas the GTI has a 38mm piston. If those Autotech rear kits are using a standard caliper with a 38mm piston, then because the piston is smaller than the pukka R32 calipers, the rear brakes from Autotech will not be as effective as genuine R32 rear anchors.
And the R32 has single piston calipers at all four corners, just like the GTI (only the R32 are bigger!).
And yes, 4/6/8/10 pot calipers often have differing diameter pistons - for a variety of reasons. Pedal 'feel' and pad wear are the usual cited reasons, but also brake noise, physically 'packaging' the pistons correctly in the caliper, and lastly, fashion can all be cited.
They made custom bells & carriers for the AP discs & calipers. I sent them back as I wasn't happy with the clearance on the lower ball joint. IMO they needed a 20mm reduction on the bell offset and the carrier altering accordingly - so, I wouldn't bother asking them TBH. I do however know someone who can engineer carriers, if you have CAD to spec.
Nice, keep us updated when you can, thanks.
