how many gears does an 18 wheeler have


How Many Gears Does an 18 Wheeler Have?

Tractor-trailers and other large trucks, commonly known as 18 wheelers, are incredibly powerful and efficient machines. But how many gears do they have and why?


Most 18 wheelers are fitted with an automated, or semi-automatic, transmission. This type of transmission allows the driver to switch between gears in the same way one would shift gears in a car. However, unlike a car, a truck transmission has significantly more gears for optimum performance.

Number of Gears

The typical 18 wheeler has either twelve or eighteen gears. This is why they are known as 12-speed or 18-speed vehicles, although the actual number may vary slightly. The extra gears are useful for adjusting the speed and power of the engine as it moves heavier or lighter cargo loads.

Reasons for Gear Ratios

A truck’s gear ratios are designed to provide extra power and speed when needed. For example, an 18-speed transmission has a steep ratio for low-end torque and low-rpm performance while the higher gears have a shallow ratio for high-speed cruising. This allows the truck to accelerate more quickly, while at the same time producing the high-end speed necessary for highway driving.

Bottom Line

While most trucks have either 12 or 18 gears, the exact number may be different depending on the make and model. However, the underlying purpose is the same; to provide the truck with enough power and speed for different types of roads and conditions. With the right gear ratios, an 18 wheeler is capable of remarkable feats of speed and power.