BRAKING NEWS How to Create the Perfect Brake Pedal Length
When it comes to making your custom brake foot box, the pedal ratio becomes important. How do you create the perfect brake pedal length? How do you know where to place your lever? What if your master cylinder is facing towards your knee instead of the firewall? Those questions all comes down to pedal ratio.
Pedal Ratio, simply put, is the length of the pedal to the pivot over the length of the master cylinder pushrod to the brake pedal pivot.
Wilwood explains it a bit better: “Mechanical leverage is simply a means of increasing the brake force without increasing your leg effort. As “A” gets longer and “B” gets shorter, the mechanical leverage increases brake force without pushing harder on the pedal. The disadvantage is that the pedal stroke also increases, requiring you to push the pedal further.”
Now, if you’re switching from a power brake system to a manual brake system, your ratios will have to change. The typical power brake ratio is between 4:1 and 5:1 while your manual brake will be 5:1 to 6:1. A 6:1 ratio is the recommended starting point by Wilwood. So let’s look at a quick example.
So, our brake pedal is 10-inches long from pivot to pedal and our master cylinder distance from the pivot is 2-inches. That gives us a ratio of 5:1. Now, let’s say you move the brake pedal 1-inch and you put a force of 100-lbs on the pedal.
The brake master cylinder will actually be moved 5-inches and see a force of 500-lbs. Let’s say you don’t like the length of the stroke? Well, we have to change the ratio. Let’s shorten that pivot point from 2-inches to 1.25-inches. That is 8:1 which now means every 1-inch of pedal travel is 8-inches of travel for the master cylinder pushrod and that 100-lbs at the pedal is now 800-lbs.
Now, lets’ say you change the shape of your pedal arm; does that change the ratio? If the direct length is the same between the pedal and the pivot, then it does not change.
If making a new shape increases the direct distance from the pedal to the pivot, then it does. In other words, if you shape your pedal arm like a pretzel but the length from the pedal to the pivot is still 5-inches, then the pedal ratio will remain the same.
Put on the brakes in the forum.>>
Top photo courtesy of forum member Cubawashere.