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The same reason the Porsche 993 Twin Turbo (the model from which these brake kits are derived) has a higher power to weight ratio than the BMW. It's a supercar with incredible acceleration and big brakes to match the power. With that much power, it's easy to get into trouble quickly.

Do you have stopping distances to show what kind of gains to expect from the upgrade?

I don't have tables that I can produce, but I can relate my experience on both track and street with the bigger brakes. I have them at all four corners of my 1996 Impala SS (4,300 pounds) and on my wife's 540i 6-speed. The biggest difference in daily use is not the reduction in distance for a single panic stop but rather it's the feel of the pedal, the perfect linearity and extremely short pedal travel before the brakes engage. There is no longer this long stroke of brake pedal travel during which the single piston caliper centers itself about the rotor and the soft rubber brake lines swell like a party balloon. Instead, there is a tiny amount of takeup as the 4 pistons of the fixed-mount caliper close the tiny gap between pads and rotors and then there is nearly perfect linear response of braking force to a given increase in force applied to the brake pedal. It is possible to be approaching a light that turns red suddenly and apply a constant pressure to the brake pedal without making constant corrections to compensate for the non-linear application of force by the stock system.

Heel and toe downshifting becomes trivial because you don't have to force your foot into all sorts of contorted positions, since the brake pedal travel is greatly reduced.

Are there any side effects due to porsches and bmw's perhaps being tuned for different front:rear weight ratio's?

Not really. On either car, most of the braking is done by the front brakes since there is a weight shift forward under braking. On a dry track with sticky tires, there is a huge weight transfer forward and more than 90 percent of the braking is done by the front. On a wet track (or street) there is very little weight transfer forward and the braking is much more evenly split. Even though the calipers are identical to those used on a rear engined Porsche, the BMW master cylinder is retained and the bias front to rear is influenced by the relative size of the master cylinder bores and the behavior of the stock proportioning valve.

The bottom line is that the mov'it kit is very balanced on the street. I've tested it quite aggressivly and have not found a propensity for either the front or the rear brakes to lock up early. In short, the answer to your question is "no"! :-)

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