Building a race car out of a normal street car isn't easy. There are a whole lot of things that need updating, replacing, or modifying before a car is ready for competition. Perhaps the most important system that needs attention is the brakes.
Most road car braking systems aren't designed for the high-stress, high-slip environment of a race track or rally stage. A street-tuned anti-lock braking system can actually hinder the driver's ability to go fast simply because it can't keep up with threshold braking and intentional wheel locking.
Other things, like the vacuum-assisted master cylinder, are just fine for street use, but as Wyatt Knox from the explains in his latest video, once you try to left-foot brake with your other foot on the gas, all that vacuum goes away, and you're left with a rock-hard, inconsistent pedal.
The solution? Well, most of the time, it's easiest to either bypass these systems, or delete them entirely. Knox also takes the time to show us the difference between a modified street car setup and a full-on rally braking system, complete with a hydraulic handbrake. Watch for yourself.