DTM

Braking systems with Opel

From 200 to zero in three and a half seconds - braking systems of DTM touring cars on par with Formula 1 The pinnacle of the season and extreme demands on race car technology - the Norisring is a synonym for both. The brakes in particular have...

From 200 to zero in three and a half seconds - braking systems of DTM touring cars on par with Formula 1

The pinnacle of the season and extreme demands on race car technology - the Norisring is a synonym for both. The brakes in particular have to handle heavy-duty workloads during the fifth DTM (German Touring Car Masters) race to be staged in Nuremberg at the last weekend in June. Nowhere else than on this urban circuit that measures a mere 2.3 kilometres are the DTM touring cars subjected to such extremes of acceleration and braking. Ultra-late braking points mean enormous deceleration rates, performed by a braking system that is on a par with Formula 1 standards.

"During the past decade, brake development has seen immense progress," says Opel works driver Joachim Winkelhock, a three-time winner at the Norisring. Obviously so, because, since its comeback two years ago, the DTM series has been specifying carbon fibre disc brakes instead of steel discs. "These carbon brakes have incredible punch, which never ceases to impress me," adds Manuel Reuter, Winkelhock's teammate in Opel Team Phoenix. Those who have had the pleasure of doing a lap in the 'racing taxi', a retrofitted Astra V8 Coupé with a front passenger seat, will certainly agree: The passenger's head is thrust forward with vehement force as soon as the driver hits the pedal to unleash the brake's phenomenal force.

Norisring has drivers braking for more than twelve seconds

The Norisring has a peculiar characteristic: A driver will only use the brakes three times during each of the 44 laps of a race on this circuit. Before entering the 'Grundig-Kehre', his foot will be on the centre pedal for five seconds, decelerating from 260 to under 50 kph, before the 'Dutzendteich-Kurve', the braking event will last about four seconds to slow the car down from 225 to just under 60 kph, and before the 'Schoeller-S', a speed of just below 200 will be reduced to around 90 kph in three seconds. With a lap time of just over 50 seconds, this adds up to a total of twelve seconds during which drivers will have their foot on the brake. The remainder is nothing but sheer acceleration, except for a bit of throttling down in the chicane.

Brakes transform more than a megawatt of energy

Ventilated 380-millimetre carbon discs and six-piston aluminium calipers at the front, ventilated 340-millimetre carbon discs and four-piston aluminium calipers at the rear - this is the standard braking system for DTM race cars, supplied by UK specialist AP Racing.

Anti-lock braking systems (ABS) are prohibited.

Whilst production vehicles achieve a maximum deceleration of 0.8 to 1.1g, DTM cars nearly reach 2.0 g. And whilst the production vehicle needs about 40 metres to brake down from a speed of 100 kph to zero, the V8 Coupé needs only 25. This high level of braking power is the result of the ratio between vehicle weight, the road holding capability of the standard Dunlop tyres and the energy transformed by the brakes.

To illustrate this point: Accelerating the Opel Astra V8 Coupé with a mass of 1,150 kilogramms - including driver and fuel - to a speed of 200 kph requires a distance of 200 metres and 6.4 seconds of time, thanks to about 350 kw (466 hp) of engine power. Decelerating the same vehicle, however, only requires a distance of 63 metres, which equates to the braking system absorbing about 1,100 kw of energy in the process. This in turn means that 1.1 megawatts of energy are transformed into heat within a mere 3.6 seconds.

Brake cooling is an absolute must

It comes as no surprise then that brakes tend to overheat. The critical point is when the heat passes from the discs, which develop temperatures of up to 550 degrees Centigrade (!), via the brake pads to the calipers, because the brake fluid reaches its boiling point at about 230 degrees Centigrade. This results in vapour locks which may lead to a 'soft pedal'. "Pit stops are particularly critical, because you keep your foot on the brake during the tyre change, with heat being continually transmitted, and this results in a higher risk of developing vapour locks," says Michael Bartels (Opel Team Holzer).

To prevent this, the brake calipers are cooled down by water. When approaching the pit lane, the driver will push a button on the steering wheel that activates a device which sprays water on the calipers, reducing the temperature to below 150 degrees. DTM regulations allow a five-litre supply of water for brake cooling. Bartels' teammate Timo Scheider comments: "Water-cooling, which is now permitted, is a major step forward that immensely increases safety, especially here at the Norisring, giving drivers a much better feeling."

Timo Scheider and Manuel Reuter use left foot for braking

One way to define the differences in driving styles is the way drivers use the brakes, with some slamming the pedal harder and others using a more gentle 'touch'. Whilst one driver may prefer more braking power at the front, another may prefer stronger braking force to be applied to the rear wheels. This distribution of braking force is adjusted via a so-called brake balance bar which absorbs the pedal force, causing pressure to be built up within the two master brake cylinders via two coupling rods. Also, there are drivers who choose to use their left instead of their right foot for braking, like Timo Scheider and Manuel Reuter.

"I've been braking with my left foot for a year and a half," says Scheider, "Because that keeps me from having to switch from the gas to the brake pedal as well as enabling me to stabilise the car with the brakes, whilst continuing to accelerate. It wasn't really that difficult to change my ways, after all, I used to brake with my left foot in karting as well."

High pedal pressure may cause muscle cramps and aches

The Norisring takes the brakes to the ultimate test, but the drivers as well. "The brake pressure you need is hard and long, at other tracks you normally spend considerably less time with your foot on the brake," says Alain Menu (Opel Euroteam) who won his first podium position at the Sachsenring. And Timo Scheider adds: "This puts excruciating stress on any driver. I once suffered a cramp because of this." The centre pedal is being slammed with ultimate force particularly at the Norisring. "It may well be that you find yourself with aching muscles on the Monday after the race," says Winkelhock. "That's why sitting properly is important for optimally applying this force." Nevertheless, aching muscles are a price that Winkelhock and the other Opel drivers will likely pay cheerfully for a successful finish at the Norisring.

-opel-

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About this article
Series DTM
Drivers Joachim Winkelhock , Manuel Reuter , Timo Scheider , Michael Bartels , Alain Menu