[Rincewind]

Fitting rear vented discs will probably require vented calipers as they will be slightly wider to accomodate the extra width of the disc.

To be honest, the only cars that need rear vented discs are the MG ZT 190's and the V6 Autos. We took the vented rears off because they don't really need them on the manual box'd cars as there is a great deal more engine braking available from the manual boxes over the autos.

The rears will never lock before the fronts do as this is illegal and the cars system has been designed to prevent this from happening with the EBD system built into the ABS unit. in the braking Regulation 13H, there is a wheel lock sequence testas part of the homologatino tests and should the rears lock before the fornts the car fails it's test therefore the EBD system takes care of it and never lets the pressure to the rears get to the pint where they will lock.

There is no need to upgrade the front discs as the system works fine with solid or vented rears as was designed to do.

Unless the brake pad material is designed to be "sacrificed" faster than normal OE pads, groved or drilled discs will not have any affect on the R75/ZT braking system.

Believe you me, the cars have been through some of the hardest tests known to driving during development and type approval and the before Australia accepted 13H braking tests, they have their own series of tests which are very hard on the car and the 75/ZT sailed through the tests and that includes taking away all brake cooling by concealing the wheels with "black out" covers to prevent airflow.

The diesel engines have a fair bit of engine braking so the vented discs aren't required. I have a ZTT 135 and I've had my car pounding round the MIRA proving ground before now doing demonstrations and I'n never had any problems with the brakes giving up.

Nic