A8 Parts Forum - Bigger brakes

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- D2 - Axles, Brakes, Suspension and Steering (https://forum.a8parts.co.uk/forumdisplay.php?f=21)

- - Bigger brakes (https://forum.a8parts.co.uk/showthread.php?t=15773)

Thanks again MikkiJayne +++ but now I'm confused. How is the flat bar mounted as there is no way it will mount flat to the upright as see in this picture :Confused: Or is the opposite side of the upright flat that's not visible in this picture?

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

Quote:

Originally Posted by Audifan (Post 158656)

Your picture is from different car. Flat bar was on S8 with Brembo brakes. Different brakes and uprights on S8 compared to A8

Correct ^

The RS4 setup is on an S8 Brembo upright whereas I am showing the Porsche 18z with the A8 HP2 upright.

Thanks for the clarification as that makes more sense.

Quote:

Originally Posted by MikkiJayne (Post 158561)

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.

Quote:

Originally Posted by Stromaluski (Post 158590)

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!

Larger pads you say...

http://forum.a8parts.co.uk/attachmen...1&d=1595235429

Porsche / Q7 18z pad vs S8 Brembo! These things are huge :eek2: Tbh I should have figured that out from the size of the caliper but it didn't really register until I had them in my hand.

Btw, cheapest brake pads on the market for a Porsche Cayenne / Audi Q7? £26 :ROFL:

For reference, this is the 18z caliper on an S8 Brembo upright - no way this will work:

http://forum.a8parts.co.uk/attachmen...1&d=1595235429

http://forum.a8parts.co.uk/attachmen...1&d=1595235429

This is the 18z caliper on the S8 345mm disc - also not going to work

http://forum.a8parts.co.uk/attachmen...1&d=1595235429

However, the pads fit the D3 360mm disc perfectly. The only challenge then is a 4mm offset in the mounting holes:

http://forum.a8parts.co.uk/attachmen...1&d=1595235429

I think this might be possible to solve by boring out both the caliper and the upright an additional 1mm and creating an offset bushing to take an M12 12.9 bolt, something like this:

http://forum.a8parts.co.uk/attachmen...1&d=1595236134

I'd have a plain one in the caliper, and the threaded one in the upright, both knurled slightly to grip the aluminium and not rotate, then they'd hold everything in place nicely. I did this many years ago to get Nissan Skyline 4-pots caliper on my Corrado :) However with this setup, its a compromise between using M12 12.9 hardware vs OE M14 10.9 hardware or removing sufficient material from the caliper to get M14 hardware in without losing strength.

Quote:

Originally Posted by 27litres (Post 158721)

Agree with all of this. +++

Lots of great information. Thanks for sharing.

I've gave it some thought and decided to go with C5 RS6 front caliper and discs since it'll be easier for me to mount the calipers. And for the rears I'm going to go with C5 RS6 rear brakes instead of trying to fit 4 piston calipers from a Boxster and custom install a hydraulic e-brake or try to custom install an additional mechanical parking brake setup.

This upgrade is something that I will eventually do and as of right now it looks like I won't be able to get around to piecing it together till next year. So I'm just looking to get as much information about it now.

The only issues you will have with the C5 RS6 rears is the Handbrake cable. You will need the cables from a LWB D2 A8. They are pretty rare. Maybe Audi heritage?