Brake Pedal Force Calculator - Calculator Academy

Reviewed By: Patrick Myers (BSME)

Enter the required master cylinder pushrod force (the force output by the pedal lever into the master cylinder) and the brake pedal ratio into the calculator to determine the brake pedal force at the pedal pad.

Brake Pedal Force Formula

The following equation is used to calculate the Brake Pedal Force from the pedal ratio and the force at the master cylinder pushrod (pedal output force).

F_{pedal} = F_{pushrod} / BPR

Where F_pedal is the brake pedal force (lb-f, N, or kg-f)
F_pushrod is the force transmitted from the pedal into the master cylinder pushrod (lb-f, N, or kg-f)
BPR is the brake pedal ratio (unitless, X:1)

To calculate the brake pedal force, divide the master cylinder pushrod force by the brake pedal ratio.

Note: Brake pedal ratio relates pedal force to master cylinder pushrod force. Converting pedal force to caliper clamping force, brake torque, or tire/road braking force requires additional information (master cylinder area, caliper piston area, brake geometry, friction, effective radius, etc.).

What is a Brake Pedal Force?

Definition:

The brake pedal force is the input force a driver applies to the brake pedal. It is a force (commonly expressed in pound-force (lb-f), newtons (N), or kilogram-force (kg-f)), not a pressure.

For example, if a vehicle requires about 50 lb-f at the brake pedal for a given braking demand, the driver would need to apply about 50 lb-f of force at the pedal. The actual stopping distance still depends on vehicle speed, road conditions, tire grip, and brake system design.

How to Calculate Brake Pedal Force?

Example Problem:

The following example outlines the steps and information needed to calculate the Brake Pedal Force.

First, determine the required master cylinder pushrod force. In this example, the master cylinder pushrod needs to see a force of 600 lb-f.

Next, determine the brake pedal ratio. In this case, the brake pedal ratio is measured to be 8:1.

Finally, calculate the brake pedal force using the formula above:

F_pedal = F_pushrod / BPR

F_pedal = 600 / 8

F_pedal = 75 lb-f

Follow-Up Calculations

If your brake pedal force works out to about 80 lb, that’s the input your leg is sending into the rest of the brake system while the pads fight whatever torque reaches the tires. A torque at the wheels estimate shows the number those brakes must overcome—for example, 3.5:1 first gear and a 4.10 axle can turn 250 lb-ft at the engine into more than 3,500 lb-ft at the wheels.

A dyno figure of 350 lb-ft at the flywheel can become a lot more torque at the tires once the gearbox and differential multiply it, so the brake pedal force you need to hold the car still depends on the drivetrain, not just the engine. Use the raw engine torque number as the starting point, then remember that low gears can make the brakes work against several times that value at the contact patch.

A 3,600-lb car with 360 lb-ft of torque has a 0.10 torque-to-weight ratio, which is the kind of setup that usually calls for a firm brake pedal if you’re trying to control repeated hard stops or hold the vehicle on a grade. Checking the torque versus vehicle weight relationship helps you gauge how much stopping effort the brake system should comfortably handle.