Brake Bias - What Is It, And What Does It Do To Your Vehicle

Brakeometer, a brake bias adjustment tool 7 photos
Photo: Brakeometer
Brake testing stand that is used to measure the effectiveness of a braking systemBMW 3-Series E46 before a brake test on rolling roadTilton Brake Balance Bar Remote AdjusterRace car driver changing brake bias while running at Road AtlantaTelemetry view of braking force before adjustmentTelemetry view of braking force after adjustment
The braking system is one of the things that some car enthusiasts take for granted, and some of them do not even think about upgrading them to match other aspects of their vehicles.
If car enthusiasts are not acutely aware of how important a braking system is to their vehicle, what about the average Joe, who just wants to drive his car and enjoy the experience?

It sounds like it does not matter, until Joe’s brakes fail and his vehicle plows into a ditch with the brake pedal firmly pressed to the floor. Average Joe then laments that the company that made his car should pay him, because they make unsafe vehicles.

A real car enthusiast will always monitor the state of his or her brakes, and the upgrades to the powertrain will be matched with immediate improvements to stopping power. However, adding a big brake kit you found on eBay is not the way to improve a vehicle’s stopping power.

This article is focused on brake bias, which refers to the ratio between the percentage of braking force received by the front and rear axle. Contrary to what some might think, 50:50 is wrong for most cars, but it is crucial to note that there is no golden ratio here.

Instead, the optimal brake bias comes if the value matches the front-to-rear weight balance, but it only applies if the balance is optimized for a precise deceleration level.

The latter means that you can tune a car to have a perfect brake bias for maximum deceleration, but this will turn it into something that is unusable on the street, but it will work for something designed to race.

The statement is true because racing car drivers will want to go hard on the brakes and benefit from the maximum capability of the system, but street cars also need to lower their speed by a smaller margin, and the previously described configuration will not operate as expected in that setting.

What can influence brake bias?

Tilton Brake Balance Bar Remote Adjuster
Photo: Tilton
The brake bias of a car can be affected by aerodynamic elements, modifying the center of gravity, different piston caliper diameters, brake pad friction coefficient, brake rotor diameter, and many other factors. The grip level of tires also affects the brake bias of a car, as does the weight placed on one of the axles.

In other words, almost every change made to a vehicle will influence its brake bias. Fitting tires that have a higher deceleration limit, also described as “sticky tires,” will increase the rear bias of a car, while fitting the opposite will bring an increase of front brake bias.

Cars with a lower center of gravity will get more brake bias on the front, while the opposite will happen to those that have had a raise of their center of gravity.

In other words, fitting a different suspension system or high-performance tires will change your vehicle’s actual brake bias, even without making any modifications to the braking system. Installing bigger rotors on the front axle, or fitting brake pads with a higher coefficient of friction on the same axle will lead to an increase in brake bias to the front.

On the other hand, if more weight is placed on the front axle, or less weight is put on the rear wheels, the rear bias of an automobile’s wheels will increase.

Motorcyclists know this best because the way their bikes brake changes when they ride with a passenger. The rear brake becomes more efficient than it used to be, but this only happens in some conditions.

What happens with too much brake bias on one axle?

Telemetry view of braking force before adjustment
Photo: Screenshot from YouTube
When a vehicle’s braking force is continuously increased, one of its axles will eventually break traction. If the front wheels lock up first, the car is front biased, while the opposite goes for the rears. 

Evidently, nobody wants his or her brakes to lock up because of an incorrect braking bias, which could even lead to an accident if the change is dramatic or it surprises the driver.

We would also note that an automotive with too much bias on one axle will have increased brake pad wear, increased tire wear on the same axle, and unpredictable handling. If a vehicle were to be heavily front biased, it would be slower than a balanced car with the same characteristics, but it will be easier to operate.

Meanwhile, if a car is rear-biased, it means that it will lock up the rear wheels before the front axle gets to experience its maximum braking force. Even professional race car drivers will have troubles driving one of these cars, especially if the rear bias had been exaggerated.

Think of this situation like driving with someone pulling the hand brake lever in the middle of a turn — you will get excessive braking power on the rear, the car will skid, and it will be slower and more dangerous than a balanced vehicle with comparable specifications.

How can you balance the brake bias for optimal distribution?

Telemetry view of braking force after adjustment
Photo: Screenshot from YouTube
Modern cars come with a technology called EBD, which only comes to those models that have ABS. This system will automatically adjust the level of the braking force sent to each axle to prevent the wheels locking up. It is not perfect, but it has been improved over the existence of ABS, which is a technology that we trust and appreciate in our daily lives.

In race cars, the driver can change the brake bias. A switch is used, and it leads to different settings within the braking system. Evidently, we do not recommend installing this in a regular vehicle, as it will not bring any benefit in day to day use, because racing drivers use these to balance out their cars as the tires begin to wear down during a race.

In Formula 1, for example, they will make small changes from one corner to another depending on how they need the car to react to their inputs.

The correct solution to the problem at hand is that the best way is to visit a specialized shop that has experience in tuning cars. Your vehicle must be weighed to see its distribution, and then you must consider the factors that might change those results — think luggage and whatever you carry in the trunk.

Tests must be made to evaluate braking ability, before and after any modification, and the suspension and its behavior must be assessed to calculate how much weight will transfer from the rear to the front while braking.

Repeated testing will bring a satisfactory result, but only if the front and rear brake components have been changed following weight distribution and the necessities of the vehicle.


Brake testing stand that is used to measure the effectiveness of a braking system
Photo: Wikipedia user ProjectManhattan
The first thing that will improve your vehicle’s braking capabilities will be a set of performance tires. They will have to be in the dimension recommended by the manufacturer of the vehicle to achieve maximum performance.

Otherwise, the increased grip brought by them could be outweighed by an imbalance of brake bias, which can happen in dramatic changes to tire capabilities.

Changes to the braking system should be made one step at a time, and investing more money in a high-performance application is recommended especially in the cases where a reputable manufacturer has taken the time of developing a dedicated system for your model.

If there is no such thing on the market, contacting a reputable shop is mandatory, because doing modifications like these through guesswork will get you a vehicle that becomes unstable under braking.

Most road cars are designed with anything between five to ten percent supplementary bias on the front than the optimal setup for their configurations. This is done to bring a reasonable tradeoff between maximum deceleration and braking stability.

The latter is something you appreciate without knowing when you go hard on the brakes while driving at high speed. Once braking stability is lost, the vehicle will become unstable under braking, which is one of the worst things that can happen to it from a dynamic perspective.

In short, do not rush to get performance braking pads or a big brake kit on a standard car without thinking of calibrating the resulting system. Never attempt to calibrate your brakes on the open road, you could kill or seriously injure yourself and others.

An example of a brake bias switch being used in motorsport applications 

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 Download: Formulas for Vehicle Braking Dynamics (PDF)

About the author: Sebastian Toma
Sebastian Toma profile photo

Sebastian's love for cars began at a young age. Little did he know that a career would emerge from this passion (and that it would not, sadly, involve being a professional racecar driver). In over fourteen years, he got behind the wheel of several hundred vehicles and in the offices of the most important car publications in his homeland.
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