Well, the 2 piston D3 calipers

• Work properly
• Are simple to service
• Don't seize up if the day has a Y in it
• Don't squeak
• Fit on larger discs than stock
• Are reliable
• Work properly (I know I already mentioned this, but I though it was important enough to mention again)

I am pretty sure the FL S8 Brembos were a fashion item rather than a technical solution, since W12 had larger brakes with sensible 2-piston sliding calipers. The RS 8-pots aren't much better in terms of maintenance, although they are very effective. I do like the Porsche 6-pots from an engineering standpoint, but I haven't ever driven with them.

The downside of the D3 385mm setup is the sheer weight of the discs - 18Kg (40lbs) each :eek2: Thats just stupid and not good for handling so I plan to fit the 360s as they are a reasonable compromise in terms of braking performance v weight v cost. Alas they won't work with the very lightweight RS6 365mm discs, but you can't have everything.

If only the Porsche 6-pots could be made to work with the RS6 discs that would be a perfect solution. I keep holding out for a set of Q7 4m Akebonos, but they rarely come up in pairs, and never when I have any money.

I'm no expert with brakes but my guess is that having pistons on both sides of a caliper have better clamping force then having pistons on the same side.

Nope. All things being equal, it makes zero difference in clamping force to have pistons on both sides rather than just one side.

Clamping force is purely a function of total piston area... on one side of the caliper. If you have two 50mm pistons on one side of a piston in a sliding caliper setup, it will provide the same clamping force as it would if there were two 50mm pistons on both sides of a fixed caliper setup. Yes, there's twice as many pistons, but that means that the pistons get half as much pressure, assuming the amount of force you put on the brake pedal doesn't change. Meaning that the resulting clamping force on the rotor doesn't change either because the twice as many pistons get cancelled by the half as much pressure. (There's obviously WAY more to it than that, but that's a pretty simplified way of thinking about it)

If you purely want your car to stop better, you'd actually be WAY better off buying better tires. Your car's limit in how quickly it can stop is purely a function of how much your tires can grip the road.

Using a more simplified example, here's something you can think about. If you can lock up the brakes on your car (assuming the car doesn't have ABS), then having even more clamping force will provide zero benefit at all. You can't make the wheels stop any more if they're already stopped. The same idea would apply even to a car with ABS. The limit of how fast you can slow down is an issue of how much grip your tires can withstand before they lock up on the road surface. Bigger brakes, more clamping force, etc won't change that at all.

Theoretically, moving the calipers outward (bigger rotors) will result in requiring less pedal pressure to provide the same amount of braking force on the road simply because moving the caliper outward provides a longer effective lever arm to act on the tire. But the bigger reason to move to different brakes is simply for other factors like increased fade resistance due to better cooling or more mass to the rotors. Or a more easily maintained setup. The sliding caliper setup is worlds easier to maintain and resist squeaks and resists seizing than a fixed caliper setup like the D2 Brembos. Not to mention, there's only like 3 companies that make brake pads for the D2 Brembos, whereas there's like 3 million companies that make brake pads for the D3 A8 brakes.

There's also handling changes to consider because adding weight to your brakes is un-sprung weight, which will negatively affect handling. However, if handling was that important... would you really be driving an Audi? Having the entire engine in front of the front axle is a terrible design for handling.

Basically a long post to simply say if you want to increase your braking capability... buy better tires.

I can't lock the wheels on my S8. I can't even trigger the ABS on dry tarmac.

This is what I mean about the 18z calipers btw:

http://forum.a8parts.co.uk/attachmen...1&d=1594823804

http://forum.a8parts.co.uk/attachmen...1&d=1594823804

The caliper lugs and the upright lugs both occupy the same point in spacetime. There's nowhere to create a bracket.

However, this is the first time I've tried with a 345mm S8 disc, and its actually pretty close. I am going to try some C5 A6 hub flanges later which sit 6mm further inboard than the D2 ones, and it might just work. I feel that these calipers would be a worthwhile upgrade from the stock Brembos, even on the same size disc as they tend to work properly for longer, are lighter, and should give more even pad contact. I'm not sure they would be better than the 360mm D3 setup though, even with the associated weight penalty. I'd probably have to try both back to back.

Sooo....

A8 upright, A6 C5 hub, OE S8 345mm disc:

http://forum.a8parts.co.uk/attachmen...1&d=1594831739

To make the S8 disc work on the A6 hub (moving it inboard 6mm) means you forfeit the splash guard, and I think the hub needs a little 'lightening', although it is possible to offset the hub up to 2mm with a laser-cut aluminium spacer so that might be a solution. The 18z caliper fits fine with a spacer washer (maybe offset by spacing the hub) and the usual bolt adapter set with a sleeve for the caliper side. The pad may overhang the disc slightly (since its 2.5mm too small), although I've seen mention of using 17z pads in 18z calipers to solve that. Still, with M12 hardware it would be possible to move the caliper in a couple of mm.

That gave me an idea...

A8 upright, A6 C5 hub, D3 A8 360mm disc:

http://forum.a8parts.co.uk/attachmen...1&d=1594831739

http://forum.a8parts.co.uk/attachmen...1&d=1594831739

This also forfeits the splash guard and definitely needs a mm or two shaving off the upright, as it is exactly centred in the caliper as-is. Its very tight on the caliper and may need a little massaging of the caliper inner radius (or machine 2mm off the disc). Again, with 12mm hardware it might actually be possible to move the caliper out a little.

Alas, none of the lightweight discs I have are even close to fitting as the offsets are completely wrong. It could be done with custom alloy bells, but thats missing the point.

I'm not sure what the pad radius of the 18z caliper is so I've ordered the cheapest Q7 pads on ebay (£26!!) to find out. I will report back at the weekend when they are due to arrive +++

Interesting.....

Thanks for info and pictures MikkiJayne +++. Curious if you have any pictures of the B7 RS4 brakes installed on a D2?

I could get fronts lock up fairly easy on my PF D2 with stock 323mm brakes but they would also heat up and fade after couple of hard braking sessions.

All of my HP2 D2s brake better than my Brembo D2s :(

http://forum.a8parts.co.uk/attachmen...1&d=1594888873

http://forum.a8parts.co.uk/attachmen...1&d=1594888873

Pretty simple really. The adapter is just a piece of 10mm flat bar with four holes in it. Wheel clearance is an issue as the caliper is quite chunky and the disc is quite flat compared to the D2 stock disc offset. I can't remember if 18" Avus clear, but the 20" FE wheels need spacers. ET needs to be 30-35 I think.

They stop very well but these discs are very prone to warping and judder and, at £1000 a set, that can get expensive very quickly! This particular car is going to get updated to C5 RS6 discs which are non-floating 2-piece and which are both cheaper and more reliable, at a small weight penalty. They also have more disc offset so we can move the caliper inboard to make more room for wheels.

The brakes on my B7 RS4 are a real bug-bear, they are just seemingly high maintenence and bloody expensive as no real aftermarket parts.

They do stop, but I'd personally look at other options unless you want to create a new headache for an 8 +++