Which brake upgrade 322 mm or 340 mm?

[DavidR]

very informative response David. so, are you suggesting a front setup upgrade which isn't as powerful so that the rears are also used more?

Well, stoptech would certainly suggest that the OEM brake setup is front biased, so a slight rear bias would optimise stopping distances.

Back to choice again for a moment, I think that any modification to the brakes is somewhat of a gamble, but I am happier following the advise of a manufacturer who (at least superficially) backs up their claims with data, rather than another (to remain unnamed) manufacturer who told send me two conflicting emails and also reccommended a kit that wouldn't fit behind my stock wheels (something I specified in my enquiries)

Sadly, there is no such thing as an objective user review. All to often people spend much money on a mod and convince themselves that it feels better, pulls stonger, has less lag etc. People by nature don't like spending a load of cash on a mod then admitting it is rubbish - so as for all the rave reviews of stoptech, movit, brembo etc - who knows?

Confused? No wonder.

[DavidR]

Thought our cars had a gadgy called EBD (Electronic Brake-force Distribution), Im no techie but the name suggests that some sort of cpu controls the amount of braking force designated to each wheel before having to use the ABS system?

Anyone care to comment?

Apparently this system is quite crude and doesn't fundamentally alter the natural, mechanical bias of the car. I beleive it works partially as an effect of ABS.

[TarmacTerrorist]

Taken from Audi homepage

Electronic brake-force distribution (EBD) and the anti-lock braking system (ABS), constitute one unit inasmuch as they share a number of the same parts. EBD ensures maximum braking performance at the front and rear wheels and under normal conditions it prevents the rear-end from braking away because of over-braking. The system counteracts “fading” as a result of overheating

[TarmacTerrorist]

Which may explain why I left Donington last year with my rear alloys dirtier than the fronts.

[DavidR]

Audi claimed that EDL was some kind of traction control on the A3 1.8T

Audi make some of the most incredible claims....

Jeff, I know you have had alot to do with the Hispec systems etc, what are your views on the optimal setup for the S4?

[Nordschleife]

Stoptech has a very good reputation in the US. They are relatively unknown in the EU.

Many of their statements about braking systems, technologies and behaviour have been driven by their inability to deliver a suitable rear brake upgrade product for several years.

I have driven Audis with stock brakes, with front only upgrades and with upgrades all round. Really good brakes on all four wheels have proved to be the best in practice, just upgrading the front brakes is acceptable for many people.

Yes, I think it is a good idea to use the very best brake fluid, and yes, I like steel brake lines. Don't just upgrade the front brake lines, upgrade the rear lines as well.

My preferred braking system supplier, Mov'it, is a European company which has submitted its brake upgrades to the testing authorities of several countries, if you wish to remain legal in Europe, make sure you are dealing with a company which supplies legal upgrades, otherwise life could be difficult in the event of an accident.

R+C

[Dippy]

.
...if you wish to remain legal in Europe, make sure you are dealing with a company which supplies legal upgrades, otherwise life could be difficult in the event of an accident.

R+C

...and also make sure your insurance company knows about the upgrade too...

[ChrisG]

Also on Audiworld was a tech article about upgrading the rear S4 to A8 discs, 256mms to 269mms a small increase in diameter but still the same calipers. Nopt sure if that is really what is needed, biger discs for a bit more torque or better calipers for greater grip of the disc.

I'm sure a lot of the difficulties relate to the, relatively, cheap materials manufacturers use. They need to be fit for purpose - ish not fit for our track days !



http://www.audiworld.com/tech/wheel1.shtml

[kozmos]

In the Feb issue of European Car Magazine, there is an interesting cover story on S4s which compares 10 S4s each with different modifications and one of the test was stopping distance. You will notice that all the cars with the upgrade brakes had significantly shorter braking distances with the exception of 1 car (this car had some problems).

I've just upgraded my fronts to STOPTECH 332mm and will be collecting my car from the workshop later today. Report to follow shortly.

[Bushy]

Well this seems all very interesting.

I can only speak from personal experience on this and can make the following comments

I originally upgraded my brake system to Quattro GMBH but this was such a waste of time and money it doesnt need talking about here. Basically the first real upgrade I did was to fit Movit 4 pots callipers on 380mm front discs with Quattro GMBH cross drilled rears. My initial thoughts were WOW, no more brake fade and tremendous stopping power, it felt like twice as good.

However on the track the issues I had were twitchy rear end on heavy braking into corners and after a cool down lap pedal feel wasnt that good ats the brake fluid got too hot

I also had an issue with the Movit discs as they seemed to vibrate from day 1, anyway QST sorted out the Movit issue by offering a deal where I would upgrade the fronts to mamoth 6 pots and get teh movit rear set up

Well, AWESOME, the pedal feel and power of braking was probably twice as good as the original upgrade. Very strong powerful stable braking. Really pleased

So my theory is that the EBD is a valve set up that when you apply braking pressure to the pedal it basically shared this force front and rear, similar to the torsen diff so any brake upgrade must be proportional in braking size. For example my original set up increased the front braking by say 50% but it managed to un balance the cars braking. When I then upgraded the rears as well it kept a similar proportion so that the EBD worked OK

Now I am not at all sure if this is true or whether I am making it up, but he braking system on my car has cost me a small fortune and I now have an awesome set up IMHO, the only trouble is I cannot put 18" rims on her due to the caliper size. Kim at QST tells me it is the only RS4 in the UK with 6 pot fronts but I am sure BArry had them on too?

Hope this helps

Bushy

[Nordschleife]

Bushy
I can fit 18 inch Winter rims over the Mov'it 6 pots with spacers, no problemo - on an RS4 you may possibly need to roll the flare a little, but hey, its that much more focussed looking that way!

R+C

[BlackShadow]

Excellent comments guys, and very in-depth analysis. I haven't responded up to now as I've been moving house. Anyway, in the end, I've decided to go for the 340 mm discs, as QST got hold of them for just a little more than the 322 mm. I shall just fit the front brakes at first as this appears to be adequate for road use.

However, I shall probably go for 2nd hand RS4 brakes with steel hoses for the rear if I use the car for track days in the future. QST recommended this as the most cost-efficient set up for track days as the fronts alone would be insufficient. Brake fluid could end up cooking because of the weedy rear brakes.

I shall report back on the difference between standard brakes and the 340mm front upgrade next week, when I've had the conversion done.

Also, going for engine chip and middle & rear exhuast (320 bhp). I chose this particularly as the increase in bhp is less than 25%, and my present insurer (Admiral) won't do cars with an increase in power more than 25%. I'll change my insurance company later if I decide to increase power further. Additionally, H&R coilovers and a short-shifter will be fitted. Can't wait.

[Bushy]

Sounds good Black Shadow, glad we were of some help

At the end of the day we have all had different experiences so sharing them means other people can gain form our errors is brilliant

Look forward to the report

Cheers

Bushy

[BlackShadow]

Right, I've had the mods done. The brakes fitted were actually Mov'it 342mm Monoblocks. Unfortunately, I have to brake like an old grannie for the first few hundred miles in order to bed the pads in. Failure to do this will potentially result in warp disks and a complete waste of money on my part.

So it goes much quicker forward now and round corners, but the road just has to be very clear for me to do it. Anyway, I shall write a full report when I've bedded the pads/brakes in.