Friday, May 30, 2008

The braking news

Much of the staggering braking performance of a Formula One car is a result of the enormous download from its wings and other aerodynamic features pressing the car into the ground. This download makes the tyres able to withstand such big braking forces. But the brakes themselves need to be able to fully exploit this force. The key to this exploitation in recent years has been the advent of carbon fibre brake discs and pads.
Carbon fibre discs operate at a temperature range of between 500–800 degrees centigrade. Below that range, the discs are fairly ineffective; above it, they begin to oxidise, that is, they begin shedding their mass in a process very similar to the rusting of metal, albeit faster. Keeping the brakes within this temperature range is a key part to a car’s performance, especially because of the regulation that limits the thickness of a disc to 28mm. (This regulation was introduced to keep a check on braking performance so that overtaking didn’t become impossible.)
The braking forces are the most impressive facet of a Formula One car’s performance. Whilst the best road cars might generate up to 1.5g (g is the force of gravity, so 1.5 times the force of gravity) under extreme braking, a Formula One car can pull over 4.5g. This level of force actually affects the blood flow to the driver’s eyes, and some drivers have noted a momentary effect on their vision. Others have commented on how tears in their eyes get thrown onto the inside of their visors. Such is the downforce and engine compression of the cars that just lifting off the accelerator pedal generates 1g – about the same as a full ABS emergency stop in an average road car. That’s before you have even touched the brake pedal!

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