Although SMW Wheels specializes in high-quality forged wheels, we are also experts in car brakes and braking systems. Both wheels and brakes are part of a vehicle’s unsprung mass and are responsible for acceleration and deceleration time, and for vehicle handling. A well-matched set of brakes, wheels and tires can help win races on the track and save lives in city driving. While many people are more interested in acceleration time than in stopping distance, the latter is a lot more important for safe driving. Whenever emergency stopping is required a few centimetres or a few seconds can make a huge difference.
Understanding a vehicle’s stopping distance
A vehicle’s stopping distance consists of both driver reaction time and braking distance. The time required to react to a particular driving challenge or situation, and when to apply the brakes, is a skill that comes with experience. But with a longer driver reaction time comes the need for a quality, dependable braking system. It is especially important for younger drivers with little driving experience, as well as for senior drivers, to be aware of reaction time and to assess the situation on the road.
While reaction time can be improved through training, braking distance is improved only through upgrading brake components.
Key Car Brake Parts
Brake rotors are round discs that are attached to each wheel and rotate along with it. The brake rotor transforms kinetic energy into heat. In cases where excessive braking is required, the heat dissipation ability of both a rotor and a wheel become extremely important. If brakes heat up to a point that exceeds their recommended operational temperature, the vehicle’s braking distance increases; i.e., it takes longer and farther to stop. Rotors are the largest of a car’s brake parts; therefore their weight is a second highly important characteristic. We will talk about the effect of brake and wheel weight on braking distance later in this article.
The brake calipers “squeeze” the brake pads toward the brake discs. When a driver presses the pedal, brake fluid moves towards the calipers, adding pressure on the piston which forces the brake pads against the rotor, making it stop.
Brake pads physically stop the rotor. When brakes are applied the pads come in contact with a rotating brake disc to create friction and stop or slow down the car. Brake pads are a wearable car brake part. The material they are made of plays an important role in their durability and the speed with which they can slow down the rotor. Almost all brake pads are either semi-metallic, non-asbestos organic (glass, rubber, etc.), or ceramic. Most modern brake pads are ceramic, because that material has good friction and heat dissipation characteristics and produces less dust during friction, thus prolonging the lifecycle of brake rotors.
Brake lines transmit hydraulic pressure from the master cylinder to the calipers, which move the brake pads towards the rotors to stop the car. When a driver presses the pedal, brake fluid moves to the calipers via the brake lines.
Key factors affecting stopping distance
Old worn out brakes can significantly increase braking distance. Modern cars typically have larger rotors which can stop faster, but it is also important to change brake pads regularly.
Tires provide the vehicle’s grip on the road–low profile tires on a larger rim tend to provide the best results. Just like brake pads, tires are a wearable component and the condition of the tire tread also plays an important role in braking.
A dry asphalt road is the perfect surface for faster braking, because it provides the best friction. But braking distance increases on a wet road or a road covered with oily liquids. A snowy or, especially an icy road, increase braking distance significantly. To partially offset this effect, many drivers switch to specially designed winter tires which provide a better road grip.
The larger the total combined mass of the vehicle, passengers and cargo, the more kinetic energy there will be at a given speed (see gcse.com). Heavier cars require either more power or more time to stop than lightweight cars moving at the same speed.
Vehicles with good aerodynamics accelerate faster, but decelerate more slowly. Cars with worse aerodynamics perform best during braking, because the airflow helps stop the vehicle faster.
Ways to shorten braking distance
1. Vehicle weight reduction
Reducing a car’s sprung weight improves braking distance, but the same effect can also be achieved with small improvements to the unsprung mass of a vehicle. According to studies, removing one kilogram of unsprung mass equals removing five kilograms of sprung mass. Installing lighter wheels and/or brakes helps significantly shorten both acceleration time and stopping distance.
2. Increase in brake rotors size
Larger rotors have better capacity to absorb energy and transform it into heat. However, larger, heavier rotors partially offset this advantage.
3. Heat dissipation improvement
Vented rotors help the brakes cool faster, thus providing more effective performance. Most cars today are produced with vented front rotors. Further improvement can be achieved by adding rear vented rotors and/or opting for magnesium alloy wheels with better heat dissipation capacity.
4. Replacing brake pads
The quality of brake pads plays an important role in stopping a car. Brake pads for city driving are usually made of materials that provide the best friction at cold-to-medium temperatures, but they may lose grip when they warm up. Racing brake pads have to deliver results at higher temperatures.
5. Installing brake air ducts
Originally created for racing cars, brake air ducts are making their way into the mass market. Air ducts work like a vent–streaming cool air onto the wheel rotors to prevent overheating.
6. Replacing tires
Like brake pads, good quality tires help improve a vehicle’s performance during braking. For the best road grip, it is important to have tires appropriate to the driving conditions. That’s why Formula one pilots have different sets for dry and wet roads. For everyday city driving the choice is usually between winter, summer or all-season tires.
Basically, all the methods and improvements suggested above fall into three categories: weight reduction, heat dissipation improvement, and friction improvement. Lightweight modern rotors and brake pads provide all three benefits, as do forged magnesium wheels accompanied by matching low-profile tires.