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Why most of trucks and busses are rear-wheel-drive?

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Posted February 25, 2018

Which one is better – front-wheel-drive or rear-wheel-drive? People are always arguing about which cars are safer, more fun to drive, better in winter and so on. However, we still have both kinds of cars on the road and they seem to be doing fine. So why there are no big FWD buses or trucks? Why literally all of them are rear-wheel- drive?

Semi-trucks carry most of the weight on the rear axles and that means front wheels have slightly less grip. Image credit: J Brew via Wikimedia(CC BY-SA 2.0)

The choice between FWD and RWD in cars typically comes down to driver’s preference. Both systems have their advantages and disadvantages.  For example, front-driven car is more stable in winter, it is less prone to oversteer, it can have a bigger luggage compartment. Meanwhile RWD car is much more fun to drive (all best sportscars have a driven axle in the rear), can have lower centre of gravity, tighter turning circle. If neither of these systems is the best, why there are no big FWD buses or trucks? Well, because they are not cars.

Drivers of the heavy means of transportation probably would laugh when hearing this question. First of all, both trucks and buses have more weight on the rear axles. Cargo in the trucks is typically closer to the rear end. Even the front end of a semi-trailer rests on the rear wheels of the semi-truck. Meanwhile passengers in the bus are also always behind the driver. Furthermore, most modern buses have engines installed in the back too. More weight means more traction – front wheels simply are pushed to the road surface less and would not have enough grip. Sure, it is possible for a bus or a delivery truck to have an even weight distribution, but there are other reasons why RWD is just a better choice.

Second reason is that aforementioned turning circle. Trucks and buses are long and, naturally, difficult to manoeuvre. This is very important for these large machines, because they work in small spaces too – bus stations, warehouses, loading docks and so on cannot occupy too much space. When front wheels are not attached to the powertrain, they can turn more.

Buses need a bigger turning angle of the front wheels to manoeuvre in tighter bus stations. Image credit: LosHawlos via Wikimedia(CC BY-SA 3.0)

Third reason is actually related to the second one. If the front wheels were driven, they would have to have mechanical joints that would accommodate the steering motion as well as turning from the engine. FWD cars have constant-velocity joints, but they simply would not survive torque of the engines of trucks and buses. Even if they did, front tires would be wearing down really quick and the mechanism would not be reliable. Trucks and buses simply must be reliable, because they have to be profitable and work for long periods between services. In this case simplicity is the answer.

Some smaller buses are actually front-wheel-drive, but only very light ones. And then there are many all-wheel-drive trucks, but they typically work in forests and other off-road conditions, such as in places with particularly harsh winters.

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