You may have seen more than one wheel standing next to each other in tow trucks carried by a truck or lorry. Two wheels are in contact with the ground, usually side by side, while one wheel is suspended in the air behind or in front of them. So for most trucks, we see a total of 6 wheels, two of which are in the air. So why do we see them in the air when there is another pair of wheels that can take the load of the others?
Today we will talk about the function of the wheels on trucks and trailers, which we usually see in the air. Many people think that this wheel acts as a spare wheel, but actually installing an axle system for the spare wheel is an extremely expensive method. These wheels have a more important task. Let’s explain why the rear wheels of trucks and trailers usually stay in the air.
The wheels hanging in the air behind the trucks are actually used when the vehicle needs to carry more load.
We can compare the carrying capacity of trucks and trailers used for heavy load transportation with the number of axles. The more the axle, which is the name we give to the part to which the opposing wheels are attached, the more load the truck can carry. In its simplest form, let’s assume that each double wheel and axle system carries a load of 10 tons. The 2-axle system carries a load of 20 tons and the 3-axle system carries a load of 30 tons. (These weights are given as an example.)
The higher the number of wheels touching the ground, the higher the fuel consumption.
When the truck or truck driver is not carrying a heavy load, he lifts the wheel up with the help of hydraulics with a button that he can control from the cabin. The reason for this is actually related to fuel consumption. If this axle system is used even when there is no need, more wheels will touch the road, it will create more friction and thus fuel consumption will increase more. At the same time, wear is reduced as fewer mechanical parts of the vehicle will rotate.
Wheels floating in the air prevent serious accidents in wheel punctures.
Of course, the presence of two wheels connected to a single axle system at the rear also gives confidence to the drivers. These wheels, which remain solid all the time, take the weight from the other wheels instead of falling directly to the rim when a wheel explodes and prevent very serious consequences.
In some tractors with 2 axles behind, the rear axle can be lifted into the air.
This axle system can be used not only in trailers, but also in tractors carrying these trailers. Fuel savings can be achieved by raising the wheels at the end of these tractors, which carry more loads without going uphill or downhill. At the same time, this method can be used for the truck to make sharper maneuvers.
Why do these wheels keep spinning even though they are in the air?
The wheels, which are kind of idle while in the air, continue to turn, albeit slowly. This is because the vehicle creates momentum as it moves. It can also be seen that while the differential they are actually connected to turns the other wheels, the remaining energy turns these idle wheels as well.
Of course, there are also trailers where this number of wheels is much higher.
Sometimes it may be necessary to carry some structures that are really heavy. Special tractors and trailers are produced for such situations. In this way, even structures weighing perhaps thousands of tons can be transported without any problems, as the weight is distributed on the axles.
Today we explained to you what the wheels in the air on the back of trucks and trailers actually do. If you want more content like this, you can write to us in the comments section.
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