Bigger brakes

[27litres]

Originally Posted by MikkiJayne

the RS6 had 19s.

In the land of Audifan, the C5 RS6 had 18's stock. So assuming they didn't change the brakes, they will fit under 18" wheels.

Originally Posted by Stromaluski

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.

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

I like your thinking, but one of the biggest factors for increasing disc size is heat dissipation.
You're right in tyres being a critical factor in how efficient your braking is, and the leverage action of larger discs and calipers, but the larger size disc also provides a critical benefit in heat dissipation.
You alluded to it a bit anyway, so I'm sure you're aware of most of this, but brakes are all about energy management.

When the car is at speed, it has a large amount of momentum which is Potential Energy.
In order to slow the car, you need to convert that energy into another form (conservation of energy).
Cars use brakes to convert all this Potential Energy into Kinetic Energy, in the form of heat.
That heat energy then needs to be added to the surrounding environment through equilibrium as efficiently as possible.

A measure of how effective the brakes are, is how effectively they can shed the heat, which is a measure of exposed surface area.
So:
Ventilated discs are better than solid discs.
Bigger discs are better than smaller discs.
Larger pads are better than smaller pads (within disc coverage limits), and larger/multi piston calipers allow for larger pads and better control.

Then there's the engineering compromises of unsprung mass, physical wheel size, metalurgy, cost etc

But as you said, none of this is any good if your tyres lose grip!