This is probably going over old ground, but I thought an extra pic or two would help.

As far as rear brake upgrades go, I'm sure the Corrado discs are the ultimate but as I don't have a welder I chose the 'bolt-on' upgrade.

SW20 (93-99) rear caliper assembly - the later models had 22mm rear discs
AW11b front discs (258mm x 22mm IIRC)
6mm 4x100 PCD spacers (I got one made up by CRN brakes for £20)





I was upgrading the front discs to slotted items so I simply moved the old ones to the back and ditched the solid rears.
While the rear discs were off I removed the dust cover to make things easier (and save a bit of weight) This was a bit tricky, requiring a dremel to cut away the metal.



I put one bolt into the SW20 caliper & hub so the caliper can swing away to clear the disc, then slide the 6mm spacer over the studs before putting the disc on. I put a bit of copper grease on the mating surfaces so they don't seize together.



Then the AW11 front disc goes over the spacer, and the caliper (with pads) can swing down and bolt up. I used a couple of wheel nuts to hold the disc in place while doing this. Once caliper is bolted to the hub, the handbrake cable and brake lines attach.



I went for longer wheel studs too as you'd lose 6mm of thread otherwise.



Although the disc diameter hasn't increased I still reckon it's a good upgrade for a couple of reasons.

1. What was solid discs are now vented - better thermal efficiency
2. More metal mass in discs means more kinetic energy can be absorbed and radiated.
3. Piston & pad area is larger - more friction & contact area.

I'm using the standard AW11 master cylinder and its still has good pedal feel. I guess if you went for the ST185/205 upgrade up the front as well you might need the SW20 Master cyl.

I'm not really sure how this affects brake "bias". As I understand it there is still the same amount of hydraulic pressure sent to the rear and thus the applied force is the same, but the rears are now more efficient and less prone to fade.

I hope this helps anyone planning a rear brake upgrade.