INTERNALLY VENTED BRAKES

Total 911 explains how Porsches past and present channel air to keep their brake discs cool

Porsche 911s owe much in terms of development to the racetrack. Racing may appear to be about speed, but you don’t win a race with a throttle. It might seem counter-intuitive, but racing is all about the slow, not the go. Brake as late and hard as possible and you can go faster for longer, carrying as much speed as possible so you can get back on the accelerator again. And it’s precisely the lateand-hard race doctrine where our tech subject this month originates.

Braking works by applying the friction of the pad material against a moving, kinetic surface (the brake drum or a brake disc). That friction creates heat, and for years that heat buildup had to be managed during racing. Brake drums gave way to become more open, solid discs 60 years ago on the Porsche 356 B in a bid to improve brake performance. Even then, drivers needed to carefully preserve materials in the brake system. Careless, aggressive use during racing built up too much heat and either the brake materials or the brake system could fail.

Enter Gerhard Mitter, a mountain racing legend of the 1960s. In 1965 he used a Porsche 906-8 Bergspyder, a legend of Porsche race cars. Weighing a scant 570kg, the Bergspyder was powered by a 256bhp (260PS) 2.0-litre, eight-cylinder engine. The really interesting component, however, sat modestly in the front axle, where the brakes use double-walled discs with a secret drilling between the walls of the disc.

The drillings channelled cooling air through the hot, spinning discs. This reduced the brake component temperatures and prevented fall-off in brake performance. Mitter was now free from the need to nurse the brakes. This meant he could brake much more aggressively at later points on the track, resulting in a clear competitive advantage.

Ever-keen to use any lessons from the racetrack, let alone one with such a performance advantage, Porsche transferred the 906-8’s internally vented brake disc technology to a production 911 as quick as it could. Just one year later, in fact, on the 911S of 1966. The technology later became standard on all 911s, right up to the present day.

Steve Mcqueen said, “Racing is life,” but Porsche freely admits to modifying that sentiment: “Yes, racing is life. The rest is automotive development.”