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A8 disc upgrades etc. Is there any point?

Discussion in 'A4/S4 forum(B5 Chassis)' started by B5QUAT, Jun 9, 2011.

  1. B5QUAT
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    B5QUAT Member

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    Hi,

    Thinking about beefing up the brakes on the 1.8TQS. Been scouting round the forums a bit and apart from the mega money Porsche upgrades there seems to be a couple of other options such as A8 312mm discs or the ECS 332mm conversion, both of which utilise the standard calliper and pad apparently, just giving you a bigger disc and are reasonable money.

    However, if the pad and calliper are the same I can't see it giving you much of an improvement as the frictional area (pad to disc) remains the same. Sure the bigger disc will be better for heat dissipation but you wouldn't really notice the difference, I don't think, unless you were on track. I can't see the brakes being dramatically better in normal use so maybe best to save up for a Boxster/ Cayenne jobby.

    I've done an AP 6 Pot conversion before on a Subaru and the difference was phenomenal, but that was going from a small 4 pot calliper and pad to huge 6 pot callipers and bigger pads and moving from 295 to 330mm discs. I'm after the same kind of anchorage really.

    Anyone done any of the above conversions that can offer any tips please?
    Last edited: Jun 9, 2011
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  2. Jason.s
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    Jason.s Active Member

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    288mm to 312mm is a nice upgrade and is worthwhile for not much money. Standard brakes are plain **** at the end of the day.

    Its not so much the pad surface area that causes the upgrade (obviously as it stays the same) but the bigger disc helps with braking strength and not just from heat factors. Best way to put it is you try and undo a bolt thats quite tight with a stubby rachet and its a damn sight harder than if you used a nice long rachet which makes things a lot easier.

    They arent going to give you a wow factor after fitting them but you`ll definitley feel a good difference and feel more confident in your braking.

    Pretty sure the boxster set up wont really work well on the A4 due to piston sizes not matching up. Aragorn knows whats what better so he`ll explain that side of things.
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    As jason says, the clamping force doesnt change, but the distance from the hub centre increases, so the torque goes up. Jasons analogy with the ratchet is a good one. By going from 288 to 312 you get a small increase in torque (~8%) for the same clamping force (ie leg input), plus a larger thermal mass so you can brake harder for longer before the system overheats.

    Pad size actually does very little, bar perhaps allowing better longevity. When calculating brake torque the only bit thats important is the average radius of the pad contact zone on the disk.

    I would take a look at using either the 320mm S4 disk and a b6/7/a6/allroad single piston ATE caliper, or the 345mm disk and caliper from a B6 S4 if you want a BIG improvement.

    64 pistons and Brembo/AP badges wont stop the car any faster than a properly specified single piston caliper, and can often screw up the brake bias and make stopping worse because they've got the wrong size pistons in them.

    Any braking upgrade also needs to be a all round thing. You cant just nail 345mm disks on the front and call it done, because if you do you'll have increased the cars stopping distance, as you'll have moved the bias forward too much.
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  4. Jason.s
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    Jason.s Active Member

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    And the arse end will become nice and lively under hard braking lol.
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  5. B5QUAT
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    B5QUAT Member

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    Great detailed replies, thanks.

    Never thought of the ratchet principle, good analogy! Obvious when you think about it.

    So if I wanted to go B6 S4 discs and callipers, would they fit straight on my TQS hubs ok or would I need S4 hubs and driveshafts?
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Hmm forgot about that bit, no they wont fit your hubs.

    You'll need to either fit B5 S4 uprights, or any B6/7 uprights.

    Driveshafts will be fine.
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