We see a lot of buses and trucks, especially during intercity trips. These gigantic vehicles, each of which carries cargo or passengers, are also modified from time to time, and we cannot take our eyes off their sparkling looks, whether we like it or not. Now we’re going to tell you about a difference in buses and trucks (or TIR) that we’ve all seen before but never thought about why.
Did you ever pay attention? The rims on the front wheels of trucks and buses are curved outwards, and the rims on the rear wheels are inclined inwards. OK, why? Let’s all illuminate this interesting difference that many of us have not thought about until now.
First of all, let’s remember what buses and trucks look like.
Above, you see a truck without a trailer behind it. If you look carefully; You will see that the front wheels are convex and the rear wheels are concave. Now let’s see what a bus looks like:
In the photo above, you see the bus. Although the brand and production purpose have changed, the front and rear wheel structure is the same. Let’s take a look at freight trucks.
As you see; Although the vehicle type changes, the design does not change at all. So why?
Why are the wheels of trucks and buses not like cars?
Passenger cars that we prefer as individual consumers have rims on all four wheels in the same way. You can see a clear example of this in the photo above. However, the situation is different for cargo-oriented vehicles such as buses, trucks and trucks.
As a matter of fact, the front wheel of a car, truck, lorry or bus has the same structure. The rims hold the tire inward. The wheels connected to the axle give direction to the vehicle with the rotation of the steering wheel. All engineering calculations made to date have revealed that the ideal rim-axle connection point for vehicles should be convex. So what happens at the back that we see concave rims on load-bearing vehicles?
The answer is hidden in the double wheel design at the rear…
As you can see in the photo above; Almost all vehicles such as trucks, vans, lorries and buses have double rear wheels. This is due to the load carrying capacity. Remember: The more axles and more wheels a tractor has, the higher the load carrying capacity of that tractor. This is exactly why trucks carrying very large and heavy loads are equipped with many wheels.
As a matter of fact, the answer to the question we are looking for lies exactly here. So much so that it is necessary to keep the double wheels used in TIR, truck or busses together. This is exactly the reason for the design difference. Double wheels used in large vehicles are connected to a single body. Therefore, concave rim design that clings to each other is preferred.
The technical drawing above actually answers the whole question. As you see; In order for the rear double wheels to be attached to the body, concave rims connected to each other must be used. Thanks to the dual rim system, a single rim is attached to the body of the vehicle, but thanks to the design, the pressure that comes with the load is shared equally between the two wheels.
So let’s summarize;
The front wheels of vehicles such as trucks, buses and trucks have the same mechanism as passenger cars that we encounter frequently. However, the rear wheel has specially designed rims so that it can be fitted with double tires instead of one and increase the load capacity. Therefore, we can say that the main difference between the front wheels and the rear wheels stems from the different design requirement necessitated by the number of tires.
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