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S4 Brakes

Discussion in 'A4/S4 forum(B5 Chassis)' started by S4twiggy, Jul 15, 2009.

  1. S4twiggy
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    S4twiggy Fully Certified Detailer!!

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    [Jul 15, 2009]
    i changed my brakes on my S4 on feb this year with original disks and pads(not OEM but not sports brakes) and to be honest im very dissapointed with them as when your doing over a certain speed:whistle2: and start braking hard they fade real quick and i dont trust them at all

    im going to get some sports brakes on there soon but not to sure which ones to go for, a couple of people have said not to go for EBC so i was thinking black diamond or summin but id like some advice from you guys who have had either manufacturers on or other make of disks and pads and which do you recommend?

    and also, wot are the OEM S4 brakes like?
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  3. Fraser
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    Fraser Member

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    [Jul 15, 2009]
    oem s4 brakes are fine for normal driving, on the track you need to be a little careful with them as they will fade

    way not look at a secondhand B5 RS4 set up ? you should be able to get a full set of fronts for £225ish

    you can also look at the rears - B6 S4 rears are a nice upgrade, just not too common to come up, main thing is to get the calipers and carriers as the discs and pads are cheap as. you need to use a small spacer with this set up iirc it is 9mm for the carriers
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  4. stapo69
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    stapo69 All hail the mighty quattro!

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    [Jul 15, 2009]
    I have EBC discs and redstuff pads on the front, thought they were ok, but a few laps of the nurburgring has pretty much killed them! They still stop me ok, but don't have massive trust in them now, so on the look for something better now, without spending a small fortune! General consesus seems to be standard S4 brakes aren't really up to the spec of the car, especially after a bit of tuning, surprising considering the size of the calipers!
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  5. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 15, 2009]
    I suspect the pads you have are ****.

    Disks are disks, regardless of where they came from. I'd swap the pads out for something decent (Ferodo DS2500/Mintex M1144/etc) and see how you get on.

    If you start fitting big brakes you need to ensure the system stays balanced, or you will increase your stopping distance. Ie fitting RS4 fronts with stock rears means that in an emergency your car will take longer to stop.
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  6. au_sjo
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    au_sjo Member

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    [Jul 16, 2009]
    Avoid EBC like the plague. Good size discs and pads like DS2500's above should be all you need for a road car.
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  7. Fraser
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    Fraser Member

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    [Jul 16, 2009]
    if you fit larger brakes you also need to adjust the abs coding for them as well as ensure the % bias is right as per aragorns post
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  8. au_sjo
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    au_sjo Member

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    [Jul 16, 2009]
    That's incorrect about the bias. The rears do very little under hard braking.
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  9. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Jul 16, 2009]
    The brake bias thing has been proven again and again. The rear brakes do very little (30%) however its more to do with piston sie and displacement and bite. than you realise.

    Over on audizine ( i will find and link in a min) it has been shown and proved it does matter, in scientific ways and in real world situations
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  10. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 16, 2009]
    heres a brief explanation of why it matters.

    Take a stock S4 with stock brakes. The LIMIT of braking is infact the tyres adhesion to the tarmac, and the stock setup will be designed so that all the tyres reach their maximum adhesion at the same time (its actually slightly front biased for safety but we'll ignore that for this)

    This means if you brake hard enough that the wheels are JUST before locking, all four wheels will be applying their maximum braking torque to the road. Yes the rears will be delivering less in absolute terms, but in terms of what the tyre CAN deliver its doing 100% of that.

    Now you fit some HOOFING great front brakes, and leave the stock rears.

    Do the same test and what happens? The front brakes even though they are huge, can still only supply the same torque to the road, as its still limited by the tyre. The problem now is, the fronts are capable of providing a lot more force, so at the point which the front wheels are about to lock, the rear is now only doing say 50% of its maximum effort, because you require less system pressure to apply enough force to lock the fronts.

    This means that with the giant front brakes, the front tyres can still provide 100% of their maximum braking effort, but the rears cant, they can only provide say 50%, so the overall braking effort applied to the road drops, and your stopping distance increases.

    The larger brakes will operate longer before overheating, so for a track the larger brakes could help, but without upgrading the rears by a similar % or adjusting the pressure bias, you WILL reduce your maximum braking effort.
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  11. au_sjo
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    au_sjo Member

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    [Jul 16, 2009]
    aragorn- I've read your explanation before and you are missing some very vital information regarding weight distribution. When you brake, weight distribution becomes very forward-biased which mean the rears don't NEED to do much because they don't have a lot of weight to stop. Increasing brake force at the front of car causes less effective weight over the rear axle which means increasing the rear braking force would potentially cause lock-up which is unsafe.
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  12. Fraser
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    Fraser Member

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  13. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 16, 2009]
    au: yes i'm fully aware of the weight transfer, and if you read what i said, you'll see i stated that the rear wheels will have less absolute braking force. Probably 3 or 4 times less, but reducing that force even further, by installing larger front brakes, WILL increase your stopping distance.

    If we bring in some completely made up numbers as an example:

    Lets assume the front tyres can apply 1000N (newtons) of force to the road surface each while under heavy braking, and the rears can only apply 300N due to the forward weight transfer that occurs. Press the brakes hard and you have 2600N of braking force transferred from the car to the tarmac.

    If you install your giant brakes, you can still only apply 1000N of force on the fronts, because the tyres haven't changed, but now at the point your massive rotors are applying 1000N to the fronts, you've only got 150N on the rears becuase your not having to brake as hard to generate 1000N on the front, total braking force now? 2300N.

    IE, Its dropped, and if you apply less force you will take longer to stop.
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  14. au_sjo
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    au_sjo Member

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    [Jul 16, 2009]
    Great theory, but in practice it makes no noticeable difference.
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  15. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 16, 2009]
    If that was true, the RS4 wouldnt have been fitted with bespoke 312mm rear disks, and every model in the audi range would have the same 240mm disks on the rear. Companies like car manufacturers WILL save every penny they can when building a car, if they didnt require larger rear disks, they wouldnt have fitted them.

    Early S4's came with 240mm rears, and audi upgraded them to 256mm ones, You think they did that because they felt like wasting some cash?

    I'm all for modifying cars, but any modifications that relate to the safety systems of the car need to be done with some sense and consideration of how they react, and responsibility for your actions.

    In practice it DOES make a difference. The "awesomeness" of the larger front brakes will simply mask this until you need it the most, in the same way that lowering your car 60mm on the stiffest springs known to man will feel awesome, right up until the point it dumps you in a hedge because the wheel cant stay in contact with the road surface.
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  16. au_sjo
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    au_sjo Member

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    [Jul 16, 2009]
    Actually, quite often in OEM's, the marketing departments have the final say on the spec, beyond what the engineers recommend.. Quite often things are done to help sell the vehicle.. Like putting four turbos on a Bugatti, when two would be better.. it's often about the bling!!

    Anyway.. no point in arguing.. next time i'm walking past the brake test rig in the plant i'll be sure to tell the guys they're wrong ;)
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  17. Crombie
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    Crombie Member

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    [Jul 16, 2009]
    If someone's after a front brake setup off a 2001 B5 RS4, a friend of mines got one for sale.

    Had a fer bit of track time on Nordschleife, etc... Always found if you do alot of late braking at speed its better to upgrade the front brakes sometimes having more pistons decent pads can improve situation and within reason bigger disks better calipers cover bases better, less likely to warp the disks. Alot of folk also forget if you stick heavier wheels on the hubs riciprical force is increased when you come off the power requiring more braking.
    Last edited: Jul 16, 2009
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  18. jcb
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    jcb Active Member VCDS Map User

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    [Jul 16, 2009]
    not so, EBC discs are made from old chocolate bars in Poland.
    they are utter *****, wharp easily especially when tracked, don't last as long either.

    I run OEM discs with yellow stuff pads. can be sketchy on first push after a cold morning.
    once they are run in they are very confidence inspiring
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  19. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 16, 2009]
    I've always just used disks from the local motorfactors. They usually stock brakeworld or QH, and i've never warped one so far.

    Brakeworld Pads are useless however!
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  20. S4twiggy
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    S4twiggy Fully Certified Detailer!!

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    [Jul 17, 2009]
    cheers lads, some usefull info your giving me, im not in the look out for big brake setup rite now as i dont need them running stock power, eventually when i get the car tuned i shall be looking at summin better but for now i jus need to get some better disks and pads i think!!

    oh and i jus found 2 nails in two seperate tyres which means i need 3 new tyres this weekend due to the spare being as bald as my mrs cat:) there goes my coilovers for another week then:(
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