If you want to upgrade your brakes, start with your tires.
If you want your car to stop faster, an intuitive start may be to upgrade your brakes. While it may sound logical, for everyday driving it will probably have no effect on your actual stopping distance. Brakes are the system responsible for turning the kinetic energy of your moving car into heat (science talk for slowing it down), however the car’s tires are ultimately responsible for how quickly this occurs.
All modern passenger cars are equipped with anti-lock braking systems (ABS). What this system does is prevent your wheels from locking up under hard braking, which allows you to maintain control of the vehicle in emergency situations. Otherwise, if the front wheels locked up, you’d lose your ability to steer. If you mash the brake pedal in any new vehicle, you’ll hear the ABS pump working, and you’ll feel the brake pedal vibrate as the ABS sorts out the right pressure to apply to each wheel. When ABS is activated, this tells the onboard systems that your wheel has stopped rotating, meaning that you’ve exceeded the maximum stopping force of the tire. In other words, your stopping distance is limited by the tire. Your brake was likely perfectly capable of applying more pressure, however the tire lost grip, so more pressure serves no purpose. If you drive a car that can lock up the brakes (nearly all can), then stopping distance improvements will be extremely minimal with larger, more powerful brake kits, assuming your ABS functions adequately.
To understand the theory behind this, tire grip is governed by a very simple equation. This is represented by F = μ*N , where “F” is the maximum force a tire can apply to the ground, μ is the coefficient of friction of the tire, and N is the Normal force on the tire, essentially how much weight is resting on the tire. The math works out nicely where the braking power of a vehicle is dictated by μ. A frictional coefficient of 1.0 means the vehicle can stop at 1 g. A frictional coefficient of 0.7 means the vehicle can stop at 0.7 g (note: this ignores external forces on N, such as downforce). With a bit of math, we can determine that a car with tires with frictional coefficients of 1.0 can stop from 60 mph in 120 ft. With μ equal to 0.7, the car would stop in nearly 172 feet. No matter how expensive or advanced the brakes are, if a car’s tires have a frictional coefficient of 0.7, there’s no way for it to stop in less than 172 feet using the disc brakes alone.
If you’re thinking everything you have learned about brakes is a lie, don’t worry.
At this point, if you’re thinking everything you have learned about brakes is a lie, don’t worry, as there are logical reasons why brakes come in prices for every social class. Admittedly glamour and brand names can play a role, but there are real benefits to expensive brakes, whether that means multiple caliper pistons, or big brake kits. Multi-piston brake calipers have numerous benefits. With more surface area pressing down onto the brake pad, you have increased clamping force, meaning less effort is required by the driver, and you’ll be able to apply larger forces in scenarios where it’s needed. Additionally, with more pistons you’ll have more even pressure on the brake pads, ensuring more even pad wear. More caliper pistons allow for larger sized brake pads, and they also ensure that the entire pad maintains contact with the rotor. As brake pads get hot, they emit fumes and debris, which travels along the pad as the rotor spins. The additional pistons while minimize the symptoms from this.
Big brake kits, on the other hand, allow for more consistent braking over long durations. Brake rotors and pads can only handle so much heat before they start to be less effective. This is known as brake fade. It’s a result of the brake pads overheating, thus reducing the amount of friction between the pad and the rotor, and reducing your braking power. Larger brake discs have the capacity for more heat, and greater heat dissipation, keeping the whole system cooler. Brake pads also are designed to be effective within certain temperature windows. A pad designed for track use will be able to withstand much higher temperatures than a street pad. A street pad, on the other hand, will be much more effective at colder temperatures, which is more common for public driving roads. If you want your car to be able to handle non-stop track abuse without worrying about brake failure, invest in quality pads and rotors. If you want to definitively improve stopping distances, whether at the track or on public roads, buy nice tires.
How much of a difference will nice tires make? Check out the video below to see my Honda S2000 go from braking worse than a Cadillac Escalade, to better than an Alfa Romeo 4C with just an alignment and a tire swap.
Writer: Jason Fenske
Published: Jul 17, 2017
Source: popular mechanics
Photo Credit: Dollar photo club