Why Do Heavy Trucks Have So Many Gears?
If you’re wondering how many gears does a semi-truck have, the answer is up to 18. Discover why that’s the case.
Those who are unfamiliar with trucks may find themselves confused about the number of gears on heavy trucks.
This is particularly true for car drivers who are used to dealing with far fewer gears. It’s even more challenging for those who drive automatics.
Be that as it may, this article is here to tell you more about truck gears and why trucks require so many of them.
What Do Gears Do?
Simply put, gears are used to transfer power from the powertrain.
To understand how it works, picture a bicycle. The gears on a bicycle transfer pedalling power to the back wheel via a chain. Similarly, truck gears move crankshaft power down to the driveshaft and eventually the wheels.
The number of gears required is determined by the truck’s size and intended use. This means that a truck could be equipped with gears of various sizes and shapes depending on their function.
Every time you switch from one gear to another, you’re doing one of the following.
- Boost force – In a gear pair, the second wheel could be bigger – as in having a higher number of teeth. While it turns slower than the other, it also carries much higher power than the other.
- Boost speed – The smaller wheel in a gear pair has fewer teeth so it will turn faster. It requires less force than the bigger wheel but could move at twice the speed.
- Switch direction – Gears that mesh together turn in opposite directions. If one goes clockwise, the other would be counterclockwise. For instance, there are cone-shaped gears in a differential that switch driveshaft power by 90° before transferring it to the back wheels.
How Many Gears Does a Truck Have?
The answer really depends on the truck.
As a rule, a truck’s size and the engine dictate the number of gears. This means that if a truck has a more powerful engine, it would require more gears.
Also, trucks equipped with a colossal engine would create enormous torque and acceleration. More gears are required so that you can have better control over that power, particularly when slowing down, stopping, or going up a steep incline.
So, how many gears does a dump truck have? 10 on average. But again, some trucks may have more for easier driving in quarries, for example.
Why Do Trucks Have A Lot of Gears?
If you are wondering why there is a need for trucks to have more gears than the average road car, here are the two main reasons.
Reason #1 – The Need to Pull Heavy Loads
A fully loaded road train may weigh over 120 tons. So, a considerable amount of energy is required to move that amount of weight, with all the power coming from the engine.
However, the torque that transfers to the wheels is at its peak at low revolutions, which is usually between 500 and 800 RPM. This means that the speed in lower gears is insignificant but you get a massive torque to move the truck from a standstill.
Furthermore, more gears on the lower end also allow truckers to increase or decrease momentum to the desired speed more effectively.
Reason #2 – The Size and Power of the Engine
Heavy truck engines are massive, and so is the torque and acceleration produced. Due to this, they must be equipped with more gears to help the driver maintain control.
For example, truckers rarely start their vehicles in the first gear, which has a very high fuel distribution and may speed up the truck too quickly. This could then cause the vehicle to spin.
To avoid that, truckers usually start in second gear, which offers a lower shoot-up effect. The vehicle takes off slower but it’s also more controllable.
In essence, extra gears are there to evenly distribute the engine’s power and make the truck easier to drive.
Do Truckers Use All the Gears?
The quick answer is no, they do not.
Instead, they often skip gears, also known as block-shifting, to avoid straining the gearbox and maintain momentum.
Now, are you wondering how to shift truck gears when there are too many?
As mentioned, you do not want to start a big rig in first gear. That applies particularly to 12-gear trucks unless you’re about to go up a steep hill under a heavy load. Also, the first gear may be helpful when you’re looking to pull off a delicate manoeuvre.
In general, it’s best to start a 12-speed truck in the third or fourth gear when it’s empty. Then, use the second or third gear when you turn on the engine according to the load you’re hauling.
The point of having so many gears is to allow a trucker to utilise the engine’s sweet spot and match RPMs to speed. It’s because the engine could sustain damage if the revolutions are too high or too low for the truck’s speed.
Truck Gears Explained
In summary, more gears on a truck allow for better handling and manoeuvring, in addition to ensuring a smoother ride.
The low truck gears are there to help a trucker overcome the challenges of the terrain while effectively pulling the load. On the other hand, the high gears make it easier to maintain momentum without introducing excess torque in the drivetrain.
Indeed, it’s going to take time to master shifting gears when driving a heavy truck, especially for those most familiar with much smaller vehicles. But, do not get discouraged, as this is where the saying practice makes perfect comes to the forefront.
And if you want to find your next 10, 12, or 18-gear truck, visit Truck Dealers Australia.
We have plenty of great choices, so you’re certain to find a gearbox that fits all of your needs.