Cross drilled brake discs.

Ok Chris, so now explain how a change of friction material (same discs, claipers, fluid and control tyres) gave the Ginetta challenge cars typically 0.3g higher stopping loads!

Hi Ken

Well it could be two different scenarios. Scenario 1 is that the existing setup suffered fade and was losing its ability to produce the required friction. The cars would start to lose braking efficiency and be incapable of locking all four wheels. A compound that permitted the friction to be maintaned to a higher temperature could give the result you found.

Scenario 2 is more complex. The brake pads have a coefficient of friction that changes with pedal pressure, disk / pad temperature and disk speed. If the less effective setup had been poorly chosen (say they were from a heavier car), it could be that the brake pads got to a certain temerature at which point the coefficient of friction became less linear and more steeply increasing with pedal pressure. This could result in being able to lock the wheels, but not being able to hold a braking force just short of locking the wheels. The property is akin to grabbiness. Changing to a pad with a more linear pressure vs temp vs disc speed behaviour in the region where the car is working would make it much easier to modulate the braking force and allow a higher stopping force to be generated. Also bear in mind that brake balance would potentially change from compound to compound if the front / rear temperature / load / pedal pressure conditions are significantly different. Throw in ABS though and the system will be sorting out modualtion on all four wheels at once, so pad choice would become less critical.

Chris