pistons in the callipers press the disc pads towards each other and against the surface of the brake disc, effectively clamping the disc between them. The friction between the brake pad and the braking surface of the disc causes heat, which is then lost to the air by dissipation through the various component parts of the brakes, so displacing energy. The more we push on the brake pedal the harder the pads are pressed against the discs, or in the case of drum brakes, the shoes against the drums, the more resistance is offered against the rotation of the brake disc or drum.
If we keep pressing hard enough on the pedal, we will cause that resistance against the rotation of the disc to build to a point where that force becomes greater than the force that is trying to keep the disc rotating and when this happens the rate of rotation will be retarded. As the disc is directly attached to the road-wheel that road wheel has no choice other than to maintain the same rotational speed as the disc. If that sequence of events causes the rate of rotation in the road-wheel to be reduced to the point where it stops, then the brakes have completed their job. Bigger and more powerful brakes WILL actually do this better than the standard equipment.
However, that is a description of how the braking effect upon the disc/drum/wheel is applied and that is the easy part. To cause a braking effect on the vehicle itself, yes you need to slow the rotation of the road wheels, but what you have to rely upon more so is adhesion being maintained between the vehicle tyres and the road surface they ase in contact with. Upgraded brakes WILL NOT improve tyre grip. We know this because if we could make a car stop more quickly by spending more money on brake parts, we would save local authorities a fortune on winter road gritting, because our ability to stop would not then be dependant upon the quality or state of the road surface beneath our tyres.
It is true that we use brakes to reduce speed without stopping, but the stop is the ultimate end in braking effect and one that requires more work from the vehicle components, but to achieve the most desirable braking effect
one has to cause the rotation of the wheels to be halted in a manner that is in harmony with the grip of the tyres - so by the time the wheels are halted, the car has come to rest also.
The automotive industry spends millions of pounds on research and development to make sure that the car you buy is fitted with components that are appropriate for that vehicle and so the vehicle will perform within an accepted standard. That performance also includes brakes, and under road driving conditions the standard equipment, providing it is well maintained, will not produce any less braking efficiency than the after-market add-ons you can buy in the name of improving vehicle performance. What the after market products do achieve is to make it easier to operate the brakes, which means having the capability to create the maximum degree of braking power at the wheels with less leg power being required from the driver at the pedal. However, the ability to reduce speed by braking is still limited by the maximum available grip of the tyres whilst in contact with the road. This is even the case with ABS, because ABS activates when the tyre is about to lock-up into a linear skid. All modern cars, and almost all obsolete ones as well, have brakes that are powerful enough to either lock wheels into a skid, or to activate the ABS from any speed throughout the vehicle's available speed range. The amount of time and distance it takes your car to stop from any given speed, providing your brakes are well maintained and are working to the required MOT standard, is all down to the friction properties (coefficient of friction) that are present within the road surface upon which you are driving and the ability of your tyres to grip on it.
So, to go back to the start of this piece, if we take our friend with his four-pot callipers, drilled discs and racing pads, unfortunately for him the claim made of improved stopping power, unless there was a fault with his original equipment, is a false sense of well-being and what was worrying when he spoke of this supposed additional stopping power, was that he also said in the same sentence that he could now drive faster because of his increased ability to stop more quickly!
In reality, what he had done was fitted components that were easier to operate, which created the illusion that they work more effectively, and would withstand much more abuse.
If you do decide you must and need to fit what you believe to be better equipment, just ask yourself what exactly it is that you are compensating for?
