Pedal Ratio is one of the most overlooked parts of a brake system. One of the main reasons and causes of a hard brake pedal is simply due to incorrect pedal ratio. When a brake pedal gets modified to “fit” in a vehicle or a booster/master cylinder gets installed where it “fits” in the car, the pedal ratio is rarely taken into consideration. Proper pedal ratio is a must when installing and operating a brake system. Below is a diagram to show how to properly figure pedal ratio:
Pedal Ratio = X divided by Y
In a manual brake system, the pedal ratio will be between 5:1 and 6:1 and a power system will be between 4:1 and 5:1. In the above illustration of the hanging pedal on the left, let’s assume the overall length of “X” is 12” and the “Y” measures 3”. That puts the pedal ratio at 4:1 which is perfect for a power system. To make this function as a manual system, the “Y” measurement would need to change to 2” giving a 6:1 ratio.
An excellent example is our Mustang kits for the 1967-1970 years. We include a brake pedal to adjust the ratio from the manual ratio to the desired power ratio. The new pedal raises the upper mounting pivot point about 2 ½”. If the correct pedal ratio is not achieved, the pedal will be extremely sensitive due to too much pressure being applied too quickly.
As you can see, if you don’t take pedal ratio into account, you are not getting the most from your brakes. If you have additional questions about correctly calculating your pedal ratio, feel free to give us a call or drop us a line--we'll be glad to help!