Even by appearance American tractor trucks are quite different from those used in the Old World. Here is a long hood, and huge cabin, often supplemented with a huge living room module. Also the big gap between the tractor cab and the place of attachment of the semitrailer must have caught the eye of many customers. Why is it so on U.S. trucks?
The big gap between the cab and the semi-trailer on American tractor trucks becomes especially noticeable when the truck is not equipped with a housing module. But even with it the frame of some models looks very long. There is a lot of speculation on the net why such a huge gap is necessary. Allegedly it is made either for safety, or for convenience of driving, or for possibility of installation of the living module. The last one is closer to reality, but still does not correspond to it.
The long frame of the U.S. tractor trucks is made exactly like this, but not for the living quarters, but for the flatbed body. In other words, it is all about unification. It is much more profitable for the manufacturer to make such trucks, which can work both as usual trucks, and as truck tractors. In the USA, a truck with a long frame can be turned from a long road train into an ordinary city delivery truck within 3-4 hours. Many trucks have ready-made sockets for hoses and electronics specifically for this purpose from the factory.
As an example, take a heavy-duty truck Peterbilt 379, which was produced from 1987 to 2007. At one time, it was an incredibly popular model of the “classic” U.S. tractor-trailer. More often than not, the 379 appears in photos as a tractor-trailer. However, there is also a 379 dump truck based on the same frame. The long frame allows installing not only flatbed body, but also additional axles. Thus, if a truck tractor Peterbilt 379 has only three axles, the dump trucks Peterbilt 379 are often equipped with an additional 4th axle, and sometimes even 5th.
As for the living quarters on tractors, it is just a “nice addition” in opened window of possibilities when using a long frame. The original intention of the manufacturer of the long frame was to unify the trucks.