skiracer

If the front/rear brake bias can be maintained relatively well using the stock rear brakes with upgraded pads, this system looks really good. The stage 4 systems use 352mm X 32mm rotors, which is 20mm bigger diameter than the BIRA system. Good- more braking surface area, bad- likely won't fit under 17" wheels (but maybe, depending on the caliper overhang). Anyone in Ohio area willing tocheck these guys out and let them get measurements off of your D2 A8? PLEASE!?!

PaulW

First, this calipers are absolutely huge! I don't think they are needed for a D2 A8. My system gives me awesome performance, plus it fits under a 17" wheel. This system won't. Wonder if it will fit under an 18" wheel.

Some BIRA guys looked at this almost a year ago....but I don't know what ever came of it. They mount in a similiar way to the stock caliper, in a longitituial versus radial direction.

All that for $1500? Looks like a great price, is it too good to be true? I wonder.

<a href="http://www.urs4.com/logbook/A6/Cayenne/cayenne.htm" target="_blank">Here's some pictures.</a>

KjellA

..which is not a good thing. And as long as the BIRA Sys 6 will give you all the braking perfomance you will ever need, why opt for something less?

Actually, choosing a even smaller (and lighter) system might be better for total performance. There will always be a compromise between great brakes and good cornering performance, as long as you can't afford the really exotic stuff of course.

ryoung

Thanks to the aluminum hats, my 355x32 mm Alcon weighs 10 lb less than the S8's original 345x30 mm rotor. In the rear, the 298x20 mm rotor weighs 4 lb less than the original 280x22 mm. Total savings with a major upgrade in rotor size -- 28 lb of unsprung weight.

In general, though, I do agree with you. Once you have enough brake to eliminate fade in the most severe service, anything beyond that becomes counter productive. I calculated that 10 lb/corner of unsprung weight is worth ~1 sec/lap on a typical 2 miles road course in acceleration, and on anything other than a billiard table smooth track, probably just as much in improved handling and cornering speeds.

TSHong

You are correct aboout the rotors, but the difference is very marginal. The D2 rotors are so small, 312mm x 25 amd weigh onlt 17.5 lb but these 352mm x 32 weigh 19.5 lb. I wonder what the Bira 6 rotor and hat weigh.

I also might be ignorant but since the calipers don't rotate, it would not be considered unsprung weight. Also, the aluminum calipers cant weight, if at all, more that the OE calipers.

TSHong

I have 19" and I guess I'm just a poser :=)

ryoung

along with the wheel bearing, upright, half of the a-arms and axle, etc. Basically, any weight that's controlled by the springs/shocks is considered unsprung weight and is bad for handling. Think of the momentum that gets transferred thru the suspension into the body whenever you hit a bump. Lighter is better because it's easier to keep the tires uniformly in contact with the road.

Rotating unsprung weight (wheels, tires, rotors) is even worse. Besides the handling issue, HP is wasted spinning this stuff up to speed, and additional braking force is needed to slow it down.

TSHong

What system or parts did you use to modify your rear brakes?

ryoung

<img src="http://pictureposter.audiworld.com/17157/rotors_rear.jpg">

<img src="http://pictureposter.audiworld.com/17157/acid1b.jpg">

These are the rotors from the "Track Sport Rear" Kit on the <A HREF="http://www.stasisengineering.com/braking.shtml">Stasis Brake Products</a> page -- but without the pads, ss lines, or brake fluid, which I already had. The necessary brackets are not shown in the photo, but Stasis uses a custom bracket and an S4 carrier to reposition the existing caliper for the larger diameter rotor. These are 298x20 rotors versus the original 280x22. Upgrading the rear caliper is more difficult because of the complications with the parking brake. Also, I had Stasis black anodize the aluminum hats black; normally they're not finished.