Go Kart Scrub Brakes
Simple in design and cheap to manufacture, a scrub brake system uses metal paddles that press against a kart's rear tires when the brake is applied.
Scrub brakes were fitted to many vintage go karts, such as my old Bird Engineering kart.
Pressing down on the left foot-pedal activates a long rod, which activates the rear cross-rod, which has two pucks of U-shaped metal pivoting on a bolt in front of the rear tires.
The efficiency of scrub brakes is dependent on the type of tires they are being used with.
Sawtooth tread tires, like the ones on the Bird kart, work pretty well with scrub brakes. But, it's powered by a 3-1/2 horsepower Tecumseh, so the kart's not going very fast to begin with.
With slicks they may work better, at least in theory, because there would be more rubber for the metal pucks to press against.
Scrub Brake Disadvantages
Aside from extra pedal pressure, continual use of scrub brakes will wear tires out faster. The more you brake, the more you decrease the life of your tires.
Another downside of scrub brakes is that, if it's wet out, the tire surface used for braking is also wet. So, in the rain, they're ineffective.
For comparisons sake, think about driving a classic car with manual drum brakes. They'll stop you, but with considerable foot pressure.
If you consider what scrub brakes were originally installed on, which were yard karts with 5hp or less engines, they served their intended purpose.
You Can't Beat Fun!