What type of brake system do semis typically use?

Semis, or heavy-duty trucks, typically utilize pneumatic brake systems. This is due to the need for a reliable and powerful braking system capable of handling the substantial weight and size of semi-trailer combinations. Pneumatic brakes use compressed air to operate, allowing for quick response times and effective braking even under heavy loads. This system provides more consistent braking performance and is capable of managing the heat generated by frequent braking in large vehicles.

While hydraulic brake systems are more common in lighter vehicles, they do not offer the necessary force required for the heavier loads of semis. Mechanical brake systems are not ideal for heavy-duty applications either, as they rely on physical linkages, which can be less efficient and require more maintenance in such demanding environments. ABS, or Anti-lock Braking System, is an advanced feature that can be integrated into pneumatic brake systems to prevent wheel lock-up during heavy braking, but it is not the primary system used. Therefore, the pneumatic brake system is the correct choice for semis.