What were you running on the front ?
Very impressed with mine in combination with stainless steel hoses and decent fluid. Majority of the braking is done at the front so rears is largely aesthetic.
Errrrrrrrrr...
True-ish, but this is largely misunderstood part of braking dynamics. How to explain though....
The limit of absolute maximum braking power on an individual wheel is actually the limit of grip between that wheels tyre and the road surface. So when you brake the wheel up to that limit, you have achieved 100% braking power. Since your car has four of these wheels, to realise 100% of the cars total braking power, you need to brake all of the wheels up to 100% of their individual limits
at the same time. This is key, since any wheels not pulling their weight (no pun intended) increase braking distances. The brakes at the front tend to do more work because of dynamic weight transfer, when you brake the car is effectively
leaning on its front wheels. A tyres ultimate grip on the world is very much related to how much weight is pushing down on it, so even though the car has four identical tyres on it, because the front tyres carry more wieght under conditions of dynamic weight transfer they have more grip and they can brake harder than the rear tyres, but we shouldn't underestimate how much of the work can be done and is done by the rear brakes.
Let's take a hypothetical 2000lb car with perfect 50:50 weight distribution (don't worry, it's not a BMW), so that at a standstill it carries 1000lbs on the front axle, and 1000lbs on the rear axle. For the sake of easy maths it's got a 100 inch wheelbase like an old Land Rover, and a centre of gravity height of 25 inches above the axle. If the car brakes at 1.0g then dynamic wieght transfer will put 1500lbs over the front axle, and 500lbs over the rear. The front brakes then can brake 3 times harder than the rears can*. But here's the thing, since the rears are still carrying a quarter of the 2000lb cars weight,
the rears can still contribute significantly.
On old cars the manufacturer sized the front and rear brakes to build this balance in, and adjusted it on the fly by fitting a load sending bias valve thst would let the rear brakes work a bit harder when there was loads of wieght in the car. The main thing for them to avoid though, was the rear brakes locking before the front ones did. This is really bad for your panelwork, so manufacturers tended to dial the rear brakes down a bit... Newer cars adjust rear brake balance using the ABS systems inbuilt pressure controls instead of an old fashioned load sensing valve, but the methodology is still much the same.
Interesting things start happening when you play with ride heights too, which might be of interest to big brake kit buyers. It's a part of chassis dynamics that gives me a headache, but I'll try to explain;
Take the same hypothetical 2000lb car as above, and (as I believe the youth of today would say) slam it.
Drop it, lighten it, mod it, and throw out your bitchin 'choonz and megawatt subwoofers so the centre of gravity height is now only 10" over the axle. Now when we brake at 1.0g, the dynamic wieght transfer is reduced so we have much less dive and a lovely flat attitude braking into the corners, in fact, we only have 1200lbs over the front axle which might be bit of a disappointment if you've spent all your dough on massive front brakes, as they're now doing a lot less work to generate the same 1.0g of deceleration. The slack is instead picked up by the rear brakes, which have been saddled with an extra 300lbs (60%) of extra weight, offering the rear tyres access to much more grip that they can use to haul the car to a stop.
Except of course we're not making use of that extra grip at all, because either we haven't modified the brake balance to suit the car's new dynamics, or even worse we've added vast amounts of brake to the front axle, and really thrown the brake balance forward. We'll still be braking the front axle to its absolute limit of grip, but that limit that is now reduced because we've altered the dynamic weight transfer and aren't putting the same load on the front axle anymore, but the rear brakes will still be braking like they've only 500lbs on them.
In short, we're braking the front wheels to 100% of their individual limits of grip, but those limits are lower than they were before we lowered the suspension. The rear brakes aren't taking advantage of their additional capacity, and are only utilising 60% of the available grip. If we've added big brakes at the front, then the pedal pressure will be lower, the balance altered, and whilst the front tyres are at the very limits of adhesion, the rears are hardly even breaking a sweat.
Result? Our lowered and upgraded hypothetical car doesn't stop nearly as well as it used to...
Doing the same thing to an S3 won't have quite such a dramatic effect as lowering my make believe one-tonne Landy by 15 inches, but if you're modifying for reasons of increased performance, it's definitely worth thinking about.
*assuming tyres with very linear responses for the sake of simplicity and ease of understanding...
- only have 3k miles on them. I had yellow stuff with mine and wasnt overly impressed with the added stopping ability. If you're going to upgrade them i think you've got to look at a big brake upgrade to do it justice. Clearly the aesthetic of a drilled and slotted is a vast improvement on the stock. I suppose if you have already upgraded the fronts and you want to continue the look then this is the most cost effective way of achieving this.
