Well, obviously not for fun …
Most likely, you’ve only seen such machines in magazines or on the Internet. On ordinary streets, cars with an additional fifth wheel at the back are almost never found. And that is true, usually four wheels are enough for a passenger car, and even three for some. Why, then, could the fifth be needed? And even some strange, as if unscrewed from a bicycle or motorcycle …
Of course, this is not someone’s prank to attract attention, and not a new device that improves dynamics or improves fuel efficiency. The additional fifth wheel is just part of the measuring system for testing vehicles. It is used for accurate measurements of speed, acceleration dynamics, and deceleration rates. A regular standard speedometer provides only approximate data, and the fifth wheel, connected to the data collection and processing system, allows you to get absolutely reliable information, up to tenths of a second.
In short, the fifth wheel is necessary for the car for accuracy. By the way, modern professional measuring systems, which are used for testing machines, sometimes do without the fifth wheel. It was replaced by high–precision optical sensors, which are just as flawless in measurements, but more compact and do not cause instinctive head turning in onlookers.