not sure, but probably due to spare wheel(fifth wheel) used to be kept in pickup bed, which is where fifth wheel hitch goes.
Not quite.
In the days of horse-drawn wagons, the fifth wheel was a...
So the trailer can flex in relation to the tow vehicle as road conditions may warrant, not only left to right, but tip forward and back as well. Now having said that, if your asking why this...
Meaning: An unneeded, extra person
Origin: This is a proverb that was first used in France in the 16th century. A unicycle has one wheel; a bicycle has two wheels; a tricycle has 3 wheels. The fifth...