Caliper and Rotor Width Mix and Matching

[CTX-SLPR]

Hello there,

Continuing my ever evolving search for a solid brake setup for my comparatively heavy '64 Riviera and I'm pretty much honing in on parts off of the newish craze of UHP SUV's like the Grand Cherokee SRT8 and various versions of the VAG platform (Q7, Touareg, Cayenne). Since I'm trying to keep as many of the parts that might need to be replaced as unmodified as possible, I'm planning WK1 Grand Cherokee hubs which gives me a 5x5in bolt pattern and that pretty much means matching rotors to be able to buy them off the shelf and not carry around spare rotors when I'm on a long road trip (paranoia I know). I am also fond of the Brembo 6 piston units found on the VAG platform but they are most commonly for a 350x34mm rotor while the Grand Cherokee WK2 "HD" discs are 360x32mm units. Is that extra mm of caliper width going to matter in having a well functioning brake system? In my mind not but I am not experienced in this.

There is also a 360x32mm WK1 disc, is that going to throw off how well the calipers work on something with as much "wrap" as the 6 piston units have?

Thanks

[stab6902]

Good to see a fellow Buick fan on here! Since nobody has replied yet, here's my 2 cents:

Personally I wouldn't be too concerned about about using a rotor 2 mm skinnier than design intent. You have to remember that new brake pads have a thickness around 8-10 mm per pad. That means that when you install your new pads on your 2 mm skinnier rotor, your caliper "thinks" your brake pads are about 10% worn. Not a big deal IMO.

If you don't let you're pads get to below 1 mm thickness before changing them, your caliper won't know you're using a skinnier rotor. Even if you wear your brakes all the way down to the backing plates, your calipers would probably be ok... I have to imagine the VAG guys left themselves a little bit of a safety factor.

Since going from a 350 mm to 360 mm rotor is only a 3% difference, I think you could get away with that too. If your goal is easy parts availability, I'd stick with a matched set of all WK parts. As I'm sure you already know, you'll need some big wheels, not to mention complementing rear wheel brakes and actuation (booster/master cylinder).

[CTX-SLPR]

Thanks for your response, I was beginning to give up hope on someone saying something. I did pretty much think the same thing as you were pointing out with the calipers "thinking" I had just worn the pads down that much. I know I've seen 1mm Ti shims for the more common 4 piston Brembos once upon a time that were supposed to help prevent heat from getting into the pistons as fast. I've not looked into them for the VAG units. Rear brakes would be a matched set of VAG units or WK1 Grand Cherokee STR8 rear units since I'm using a whole WK1 Dana 44 rear axle. VAG units are 330x28mm while STR8's are 350x28mm, same thickness so assuming mounts can be fabbed (like everything else on the car practically) I could use the VAG calipers on the SRT8 rotors. A full set of VAG stuff seems to be cheaper than the SRT8 as well.

I'm planning on using the specs (if not an actual OEM wheel) off of WK2 Grand Cherokee since they have a nice high offset to cut my nasty scrub radius down to something more in like with stuff like a C5/6 Corvette and the like. Debating between 18in wheels (less "cool" OEM offerings but more sidewall) and 20in wheels mainly since 19in tires are stupid expensive compared to 18 or 20in units. I like the 18's since with a 255/55R18 it gives me a good sidewall for both looks and comfort vs. the 255/45R20 offerings. However fitting them over the fixed calipers seems like it could be a challenge.

Thanks

[stab6902]

Sounds like a good plan. Make sure you match the master cylinder diameter (and ideally stroke) to whatever brake package you end up going with (assuming you're going with power brakes). Again, I'd stick with everything out of one vehicle to make your life easier. You'll still need an adjustable proportioning valve since newer vehicles use the ABS unit for electronic brakeforce distribution.