If you drive a car and are the least bit observant, you might have noticed that your car dips forward when you apply brakes. The nose of the car takes a downward dive and your body in the car moves forward as well. The moment you let the brake pedal go, the car takes the weight of the front shocks and levels up. This behavior of the car is there by design. Automakers design the car with most of the braking force going to the front wheels than the rear wheels. And this is what is called the brake bias.
Brake bias and motorcycle riding
Brake bias is as important as maybe brakes themselves for the car to stop on its toes. The car will not stop quickly if the brake bias is skewed in any way. All the motorcycle riders reading this blog are well aware of the importance of brake bias. Whether it’s a sports bike, a cruiser, or a street bike like your average 70cc bike, you need to manually balance how much brake you want to apply to effectively stop the bike. A bike rider knows how much foot work, as well as hands, are involved in order to stop your bike. Just applying rear brakes on a motorcycle is not going to slow it down quickly and there is a very high chance you are going to skid. Also, just relying on your front brakes is equally dangerous.
Experienced bike riders learn with the passage of time how much brake should be applied both at the front and the rear, and that too simultaneously, for the bike to stop as soon as possible. Newer fancy heavy bikes now come with several rider safety features including the anti-lock brake system.
However, in cars, you do not have separate front and rear brakes. This is where automakers have to be extra cautious and extra clever with the setup of their vehicles. Some of you might still remember how skid-dish the post -2001 Toyota Corolla (9th generation) was. It cannot be said for certain that the 9th gen Corolla had specifically a brake bias issue. There were definitely more variables playing their part in making the car skid and slide everywhere. A vehicle must be manufactured/tuned to stay balanced under heavy braking.
Brake master cylinder
Almost all modern super cars let you change the brake bias to some extent through their multi-info system. But we are talking about normal econo-boxes here. Your regular family sedan/hatchback doesn’t have anything remotely that sophisticated. Your regular cars have just one master cylinder, unlike racing cars that have two master cylinders (separate unit for front and rear brakes). And in a non-automobile scenario, a master cylinder like apparatus will apply an equal amount of pressure (force) unless there is something in between to adjust how much force should be applied.
Brake bias valve
So to adjust how much brake will be applied at the front compared to the rear, a brake bias valve is used. It is also known as a proportioning valve. The valve adjusts the brake fluid pressure in order to keep the car balanced under heavy braking. The valve directs the brake fluid according to the preset pressure values. It reduces the amount of brake fluid pressure traveling to the rear brakes in order for most of the brake force going in the front. The brake is distributed between front and rear by the ratio of 3 to 1 (3/4th of the force is applied t0 the front, and 1/4th is applied to the rear).
The brakes have come a long way from what they used to be. Once all we had were drum brakes for both front and the rear wheels. And a drum brake locking up in the case of overuse/overheat can be extremely dangerous. Also, if all the brake force is being applied to the front, even if you have disk brakes, you will end up locking the tires. The goal is to stop the car as quickly as possible without any tire lockup. But there is another important thing to keep in mind here. These brake valves do nothing under normal conditions. They have no restriction in normal conditions and brake fluid will pass without any curtailment. Its when more and more pressure is applied that the valve starts to restrict the brake fluid flow, hence reducing the brake force as a result.
Electronic brake-force distribution
However, all this brake bias ‘chicanery’ isn’t an issue when it comes to cars equipped with EBD (electronic brake-force distribution). Cars that come with ABS+EBD adjust how much brake bias is required when it detects the cars is slipping. The electronics in the car detect variables like speed, brake force, tire skidding, and even steering angle in some cases, to apply automatic braking in order to keep the car straight even in under heavy braking. And since EBD takes all the information in runtime and from the wheels (ABS sensors on all 4 wheels), there is more accuracy compared to something mechanical like a normal proportioning valve.
Brake bias is an important aspect of driver and road safety. Automakers do a lot of research before launching a vehicle. So it is not advised to play around with such a critical part of the puzzle. If you have an issue with your vehicle’s braking, have it checked by an authorized workshop or a trained technician.
Pakwheels collection for: Race Bikes