Off Road Braking Basics
Understanding Pedal Ratios, Bore Sizes, and Line Pressures
Brakes are rather simple when you think about it; you stop if you have them and crash if you don’t. Somewhere between these two extremes lay the majority of our own brakes and, for the most part, they usually function pretty darn well.
But for those of you who swap brake parts to build custom creations or are saddled with a project that wasn’t done right, this story will give you the basics on the three little-understood aspects of a hydraulic braking system that have the greatest impact on how well it works: pedal ratio, master cylinder bore size, and hydraulic line pressure.
One of the biggest braking problems occurs when a stock vehicle, after it’s had 1,000 pounds of accessories added and bigger tires slapped on, just won’t stop like it used to.
If you’ve ever noticed the drum and rotor differences between a 1/2-ton and 3/4-ton truck, it’s obvious that size does make a difference. The heavier-rated truck is capable of carrying a heavier load, and the larger brakes are properly designed to safely stop that theoretical maximum weight.
Does that mean your overweight Suzuki needs 1-ton-rated brakes for the ultimate in stoppage? No, because the extra weight of the components themselves would outweigh the advantages. While the ideal situation is to figure out what you need as far as stopping power, most people are unaware of how to do it. The standard answer is to replace drum brakes with discs, but disc brakes do not necessarily stop better than drums, due to the larger frictional area of drum brakes and their self-energizing feature. However, disc systems definitely work better in the ‘wheeling world, because they offer consistent operation in high-heat and wet situations and are much easier to maintain and adjust. Whether you go with discs or drums, safe, effective braking is the ultimate goal. Achieving that requires either the hit-or-miss approach of parts swapping, or a real understanding of the relationship between your foot pressing on the pedal and the tires grabbing the ground.
Probably the three most misunderstood factors that affect braking performance are pedal ratio, master cylinder pressure, and master cylinder volume. If these three items are correct, other issues such as the type of lining material and brake-biasing procedures can easily be handled. For example, if the custom brake system on a truck doesn’t stop it sufficiently many owners will just throw on better brake pads, when in reality the pedal ratio or the pressure or volume to the calipers may be wrong.
In addition to explaining these braking mysteries, we have also included a few tricks and tips, along with some associated formulas for figuring out how to stop your rig in the real world, that we’ve learned through our own hit-or-miss upgrades.
But remember, the braking system on your vehicle is one of the most important aspects regarding the safety of yourself and others. If you cant modify the braking system correctly, dont do it at all. Its far better to leave this type of work to the experts than to end up in a ditch, or worse.