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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 |
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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.
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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! |
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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. |
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Lots of great information. Thanks for sharing.
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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?
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