"Shawn" shawn_75ATcomcastDOTnet wrote in message
...

"Pete C." wrote in message
...

That four wheel setup is a "full trailer", where the trailer wheels /
axles support the entire weight of the trailer and the draw bar only has
a pulling load.

The normal OTR rigs you see are as you note "semi trailers" where part
of the trailer weight is supported by the tow vehicle. The converter
dollies used for tandem setups convert a "semi" trailer to a "full"
trailer.

Permanent full trailers are typically low speed setups seen in farming,
mining and circus uses.

Pete C.

Thanks for that! I have often been curious where the term "semi" came
from.

Shawn



Actually, I believe that the word, "trailer," refers to a unit with one axel
or with several that are close enough together to act like one. When you
have wheels at the corners, the front set of which steer, the rig is
generally called a "wagon."

The word, "semi," is a contraction of semi-articulated. A fully articulated
vehicle bends in the middle but steers at both ends (think some fire engines
and large city busses...). A semi-articulated vehicle bends in the middle
but only steers at one end.

But, such terminology is always a bit dicey, since local usage may vary...

Jerry