18 Wheeler is pretty self explanatory, Tractor Trailer makes perfect sense. Where does the the term Semi come from? Is it an anagram? Self Equipped Mobile... something? It's not like it's kind of a truck, but not quite.
The way it was explained to me.... The term is derived from the trailer not the tractor. A standard trailer is designed to support most of it's weight on it's own axles and place a small amount of weight on the towing vehicle. (Think about a bumper hitch trailer on your pickup.) A "Semi Trailer" is designed with rearward mounted axles and places approx. half the weight of the trailer and load on the towing vehicle. 18 wheelers are properly refered to in this setup as Semi Trailer Trucks or Semi for short.
I would have stated it differently. A "full" trailer has axles at front and rear. A "semi" trailer has axles only at the rear, and the front must be supported either by the tractor or the support legs. A semi trailer can be converted to a full trailer with an "articulator", "converter dolly", or whatever you name that set of axles with fifth wheel. A tractor is made for towing a trailer. Various styles of "doubles combinations" have a tractor towing a semi-trailer followed by a semi-trailer converted with a dolly. A truck has a cargo body or flatbed. A truck may tow a converted or full trailer, but virtually no weight is transfered from the trailer to the truck. A tractor with dromedary box or flatbed has cargo capacity and also a fifth wheel for towing a semi-trailer.
That was a great reply made by heyns57. My last job before I retired we drove Truck and Trailers. Alot of back east drivers do not know what that is. Just like you explained a truck with a cargo tank mounted on the frame or a tank mounted to the power unit and pulling a full trailer. There's no fifth wheel because instead of the converter gear the trailer is mounted to a turn-table and is never disconnected. The full trailer is hook to the truck by a pintle hook. The truck pivots in two places and is easy to get into small areas. That's why you'll see alot of west coast gasoline companies use this set up. The stations are old and built for small pup trucks and nowadays we use the bigger trucks but have to get in the same area. Then if you go into NV,OR,WA, and some other west coast states you'll see the jumbo tankers that are 85' long. But I can guarantee you that 85' truck&trailer can get into closer areas than a 55'semi. Thanks for the great explanation.
I had never even thought about asking those questions. I guess you learn something new every day.. Thanks to all of you.
A tandem dump pulling a four-axle full trailer dump was a common combination in Michigan in the 1960s. I never thought of it as a truck and trailer. An acquaintance said that he would use only the lead on short hauls, and the combination on hauls of more than 50 miles. Before twin 28s were authorized in Wisconsin, my employer Chippewa Motor Freight operated truck and trailer freight boxes from Chicago to St. Paul. The same 28' doubles that I pulled in Illinois could be used through Wisconsin when pulled one at a time by a straight truck using a converter dolly with a very long tongue.
