Anyone who has ever driven a standard car will have a basic understanding of how gears work. Press the clutch down and shift to a higher gear as speed increases, or downshift to slow down.

The same basic principle applies to an 18-wheeler, except it is much more complicated.

How many gears does an 18-wheeler have: An 18-wheeler has a powerful engine and a transmission with between 10 and 18 gears. Usually, two of these gears are for reversing. A clutch needs to be pressed to move between the gears and there is a narrow band for each gear, so truck drivers have to shift constantly.

While manual transmissions were standard for semi-trucks, there has been a growing trend towards automatic transmissions. Still, veteran truck drivers can sometimes be sentimental about manually shifting gears in their big rig.

Why does a semi-truck have so many gears?

A semi-truck can have between 10 and 18 gears, depending on the size and how the engine is constructed.

When learning how to drive a semi-truck, trainees will be educated on basic shifting practices.

Then, if they drive a semi-truck that has more gears than they are used to, drivers may undergo additional training so they are as comfortable and safe on the road as possible.

The reason why 18-wheelers have so many gears

A semi-truck engine is built differently than a basic car. For starters, the engine is much larger, and with more size comes a need for more gears.

There are different types of transmission systems: automatic and manual. Manual transmissions will have more gears so a driver needs to learn how to shift and when to shift.

There are also at least two gears that are for reversing, unlike the standard one reverse gear for cars.

Again, this has to do with engine size and speed.

Are semi-trucks manual or automatic?

It used to be the norm that all semi-trucks were manual. Seasoned truck drivers will often still prefer a manual transmission to an automatic transmission.

The transition to automatic semi-trucks had its issues. They weren’t always reliable, which made truck drivers not want to adapt to the new system.

However, nowadays, many semi-trucks have automatic transmissions. The technology is much more reliant and it is easier to drive an automatic.

How do gears work in an 18-wheeler?

How do gears work in an 18-wheeler

Understanding how gears work for an 18-wheeler is important but any truck driver will tell you that you need to go beyond just theory to really understand. Each truck will have its own personality with its engine and transmission, with some clutches being harder to work than others.

Furthermore, while you should know the basic speeds at which each gear can achieve, once you’re on the road, listening to the feel and sounds of your truck becomes intuitive.

Still, the basic premise of semi-truck gears is the same as with a car. Start in the lowest gear to get the truck started and slowly work your way through the gears as you get to higher speeds.

Likewise, shift into a lower gear as you want to slow down your truck. Finally, use the reverse gears to back up your truck.

Even though semi-trucks come with a first gear, the power of their engine means you can actually start in second gear. With the first gear comes a higher level of fuel distribution, which means your speed can increase a lot faster.

Starting in second gear for a semi-truck means you have more control over how fast you accelerate, which creates a much safer environment.

How do you shift gears in a semi?

The gears of a semi-truck are configured in an H-form. The first gears, up to the fifth gear, are similar to that of a car.

Then, when the driver wants to go faster, they need to split the process to reach the higher gears.

The biggest takeaway with semi-trucks and their gears is that the power bands are very narrow. In fact, the difference is only about 750 RPM per band, so a lot of shifting takes place before a cruising speed is attained.

As you can imagine, driving a semi-truck on an open highway is much easier than having to constantly shift in city streets with multiple traffic lights and a high volume of traffic.

How do you brake in a semi?

You can simply press the brakes, but especially with a fully loaded trailer going 60 mph, braking is not a simple act with a semi-truck. It’s much better to work your way down through the gears before you brake, which takes a bit of practice to accomplish.

There is a lot of torque in the engines of semi-trucks, so having a range of lower gears will help cool your engine and allow you to stop smoothly.

Advantages of automatic transmission

As we mentioned, most newer semi-trucks now use automatic transmissions. They are well-built and reliable.

An automatic transmission in a semi-truck relies on computer-like technology to adjust the gears as you apply more gas to the engine. It has pre-programmed RPMs so it knows when to shift automatically.

The benefit is that your gears are shifted seamlessly and there is no accidental grinding. As a result, the transmission should last longer.

Another benefit is if you are a new truck driver and your routes involve congested areas. Even though truck drivers get used to the system fairly soon, it’s pretty nerve-wracking to be stuck in traffic and worried you won’t be able to shift in time or worse, stall when you are trying to get your truck moving in the middle of a busy intersection.

The clutches on semi-trucks are also very heavy and prone to getting stuck. You may have an older, temperamental clutch that takes getting used to. An automatic transmission won’t have a clutch pedal accessible to the driver, so this is one less thing to worry about.


An 18-wheeler can have between 10 and 18 gears. The RPM band is quite small for each gear so a lot of shifting needs to occur. However, many new trucks now have automatic transmissions, so there’s less need to worry about gears.