Why do people incorrectly call an 18 wheeler a "semi"?

OneHoof

I was a truck driver for seven years in the United States. My understanding was that the term semi comes from the most basic definition meaning partial or incomplete. When driving a road tractor without the trailer, the truck would actually NOT stop as fast, because the laws of physics push the vast majority of the truck's weight onto the steer tires when braking... So, ironically a tractor which is incomplete (or semi complete) takes longer to stop then a tractor which is complete with its trailer. This is true because when you have a trailer with a load, you have the weight of the load keeping pressure on 18 wheels which with the tractor, trailer combination together has 5 axles, which have 10 drum brakes stopping capacity. If you ever watch a truck driving without its trailer you will notice its rear drive tires bob up and down... especially when not on a smooth road. Hence truck driver's call the tractor... which is incomplete and NOT as safe without its trailer, a "bob tail"... because while going down the road, it's back end or tail is bobbing up and down. So, on the CB... other truckers either call a truck without its trailer a bob tail a bob tail or a semi... meaning the truck was incomplete. In my 7 years of truck driving I have never heard the trailer called a semi... I have heard a road tractor called: a tractor, big truck, a ten wheeler, rig, but most often a "bob tail" or just a "semi truck". My understanding has always been the tractor is called a "semi" because it was incomplete, and NOT as safe to drive without the trailer. I came on this web site because my brother in law told me he looked up "semi" in the dictionary and that I was wrong. He claimed the dictionary referred to the trailer as the "semi". So, I want to correct myself if I am wrong. Hence, I came here to do research... and tell what I know as an experienced drive Jan 02 11, 7:14 AM

OneHoof

I was a truck driver for seven years in the United States. My understanding was that the term semi comes from the most basic definition meaning partial or incomplete. I came on this web site because my brother in law told me he looked up "semi" in the dictionary and that I was wrong. He claimed the dictionary referred to the trailer as the "semi". So, I want to correct myself if I am wrong. Hence, I came here to do research... and tell what I know as an experienced driver of 18 wheelers. Which still makes sense... the trailer is also incomplete without a tractor. I guess actually even more so because it can't even move without the tractor's tires to complete it. Of course, for several years it has driven me nuts when a news reporter says a "semi" has overturned on the interstate... and in the same breath say, it will take hours to clean up as crews are unloading the trailer by hand because either way, it is incorrect to call a tractor with its trailer a semi because "semi" means incomplete... and when they are both together they are complete and hence no longer "semi". Granted, the misnomer "semi" the reporter uses, is so over misused that the average radio listener accepts the incorrect term as normal vernacular. I guess the reporter uses "semi truck"... so people know it is an 18 wheeler or road tractor. Again, this gets on my nerves because either way, neither the tractor, nor the trailer are "semi" (incomplete) when they are attached to each other. So, the bottom line is: If the tractor is attached to a trailer you can no longer "correctly" call the combination a semi. It has now become a tractor (meaning to pull) and a trailer (which means to be pulled behind). So, from my perspective, I have always called my road tractor a "semi" truck, because I know it is semi complete without its trailer and I have to use extra caution and di Jan 02 11, 7:17 AM

OneHoof

So, from my perspective, I have always called my road tractor a "semi" truck, because I know it is semi complete without its trailer and I have to use extra caution and diligence when needing to stop, to keep from skidding. My brother in law caused me to realize... the trailer is also "semi" complete without its tractor to pull it where it needs to go. I will look into this deeper and let you know what I find. Thanks for reading. One Hoof Jan 02 11, 7:19 AM

OneHoof

The vehicles commonly referred to as "semi trucks" are often the biggest vehicles on any stretch of road. Considering that "semi" means "half," it's natural to wonder, semi-what? The answer is: semi-trailer. Trucks The typical truck you see on the highway consists of two parts: the tractor and the trailer. Tractor The tractor is the part that does the pulling. It includes the driver's cab and the engine, and it can get around on its own. Trailer The trailer is filled with cargo, and it is dead weight. It's not going anywhere without a tractor to pull it. Semitrailers If a trailer has wheels on both ends and is pulled behind the tractor, it's a full-scale trailer. If it has wheels on only the back end, and the front rests on the tractor itself, it's a semi-trailer. In common parlance, then, a "semi" is a tractor pulling a semi-trailer. 18-Wheelers The most common tractor-trailer configuration in North America is the 18-wheeler semi. The tractor has a front axle with two wheels, and two rear axles with four wheels each, for a total of 10. The trailer has two rear axles with four wheels each, for a total of eight. Source: Turek Trucking: Tractor/Trailer Terms Read more: Why is it called a semi truck? | Answerbag http://www.answerbag.com/q_view/1941761#ixzz19t7qsrxd Jan 02 11, 7:32 AM

OneHoof

Okay... it looks like my brother in law's research is correct. The trailer is called a semi because it does not have wheels in the front. Hence, the tractor is called a semi because of the trailer and not vice versa. However, I still maintain, from my 7 years trucking experience, that the tractor does NOT stop as well without a trailer. Therefore, the tractor is ALSO semi complete without its trailer. Regardless, by definition of semi meaning incomplete. It in my opinion, would still be incorrect to call a tractor trailer combination a "semi" because when together they are complete and no longer semi. Jan 02 11, 7:36 AM

OneHoof

It is incorrect to call a tractor trailer a "semi" because by definition, semi means incomplete. However, like most misnomers... It is so commonly used that the average person knows what the speaker means and that's the depth of the conversation ends there. I guess because we often don't think about the meaning of a lot of the words we use. As a truck driver... I took it to heart that my tractor was "semi" complete without the trailer, because without the weight of the trailer pushing down on the fifth wheel the tractor's back end "bobbed" up and down for a rough ride and it did not brake as well. Also, the four extra drum brakes on the trailer helped a little too. Jan 02 11, 7:48 AM

OneHoof

As a "semi" truck driver... I took it to heart that my tractor was "semi" complete without the trailer. Whenever I drove without the weight of the trailer pushing down on the fifth wheel the tractor's back end "bobbed" up and down for a rough ride and it did not brake as well. The trailers weight mainly helps because it puts weight on the eight drive tires, which stops the bobbing (bouncing) and makes the drive tires brakes much more effective. Also, the four extra drum brakes on the trailer help some, but not as much, because during braking the inertia throws the weight towards the front of the tractor trailer. So, not as much of the weight is on the 8 trailer tires. Jan 02 11, 7:53 AM

OneHoof

Originaly, I was more focused on the tractor being "semi" complete without the trailer. Of course, I never thought of the "lonely" trailer sitting in the yard all by itself being "semi" complete too. At least the tractor could drive itself around, even if its tail bounced and bobs up and down... and it doesn't stop as well without (its other half) the trailer. Which faithfully, as a bumper sticker on the back of a trailer said: "I go where I'm towed." LOL Jan 02 11, 8:17 AM

OneHoof

The bottom line though is this. The tractor trailer is a team effort... just like a team of horses pulling a wagon. The tractor is not complete (semi) without the trailer and the trailer is incomplete (semi) without the tractor. But hey, (Wonder Twin powers activate) when the tractor and trailer get hooked up (literally) they ultimately complete each other and are no longer incomplete (semi). Therefore, once the tractor backs up under a trailer, the king pin slides into the slot of the fifth wheel and locks and the landing gear on the trailer comes up. That tractor and that trailer are now "complete" (no longer "semi"). So, as long as a tractor is attached to a trailer... it is from that point a misnomer (incorrect) to refer to this "team" as being "semi". It is now, officially a "tractor trailer combination"! Jan 02 11, 8:29 AM

Datsmeharse

See Question #41314. Jan 02 11, 9:55 AM

OneHoof

Actually I did read question Question #41314, but at first it was so old it wouldn't let me respond. So, I refreshed with a slight varation. I'm still researching the finer details... But it appears that while it is correct to call it a "semi trailer", in reality a "semi trailer" can never drive down the road without a tractor pulling it. (If you ever somehow see one doing this RUN something is VERY wrong!!!) LOL. So it just naturally seems to make more sense to me as a truck driver to call the combination... a tractor trailer or an 18 wheeler. *wink* Jan 02 11, 10:37 AM