Interesting Facts About Semi Trucks And Eighteen-Wheelers

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1. Recently I just started a job into the truck driving industry. The company I work for has automatic transmissions and we also have the ability to gear them down when necessary. Was told to use the manual part as well as the jake on deep down grades. But here is where I have a very serious question. When it comes to where a sudden stop is mandatory. To prevent injuries to another motorist, to ourselves, and to the semi. Can I manually gear the truck down, still using the jake to get the semi to stop and this will not cause transmission problems? We all know to look ahead for brake lights but things happens when they appear out of advance warnings. I had used this method before, switching to manual and hitting the lower gears, also having the jake on. I was told this is not a time to use this manually gearing down…My thought are, if it’s good for one way of holding back, why should it not be used this route? Can someone please tell me why I cannot do this? Does this wear on the truck? I need a reason why answers not just because you just shouldnt do so answers or otherwise I am not going to understand how it can hurt….Thank you

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   • A sudden stop or an emergency would require very fast responses, brake hard and steady and use the anti-lock to steer around your problem, or stab break and stop in a straight line. The engine brake and downshifting require too much time. these methods are designed for controlled breaking down hill, or a planned slow down like an exit ramp.

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2. Hi Dan I really find all your information of great interest because I am planning to start training to get my CDL license so I will just go over these until I can get more information, thank you.

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3. if i add 4000lb to an 18 wheel trailer 3/4 of the way to the rear of the trailer. what will be the increase to the truck axles( both front and rear axles)

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   • it depends on what pin hole your trailer tandems are in and where your fifth wheel is. you have too many variables, better to just scale every time.

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   • If there are only 2 pallets of beef in the trailer (4000#) it doesn’t matter where the pallets are placed in the trailer. However if the pallets of beef were in the middle of the trailer , the truck would ride smooth !

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4. Hi I’m up to get my CDL license can sum one give me a web site to go on for a lil more studying

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   • If you’re looking for CDL practice tests, we have several here that are highly recommended: https://www.thetruckersreport.com/cdl-practice-tests/

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5. Samuel – You made an error in your drawing on what “wheelbase” is, and the distance is wrong also. Wheelbase is not the width of a truck, from outside of tire to outside of tire, that is the “track”. Wheelbase is “always” measured from a front axle/wheel to a rear axle/wheel, not from side-to-side. Wheelbase of a tractor/truck (measured between rotational centers of wheels or axles) is measured from the front axle/wheel of the tractor/truck to the rear axle of the tractor/truck. The overall wheelbase of a tractor-trailer will be measured from the front axle/wheel of the tractor to the rear axle/wheel of the trailer.

   Above you show a wheelbase at 245″ – 265″, that is 20′- 5″ to 22′-1″, only the enormous CAT and EUCLID off-road trucks are that wide.

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   • Actually, wheel base is measured from center of front axle to center of rear axle group. if you have tandems at the rear, you would measure to the center of the tandems, if you have three axles at the rear of the tractor, wheel base would be measured to the center axle. if you have only one axle at the rear, wheel base would be measured to the center of that rear axle. if you have a lift axle and two drive axles, the wheel base would change as you raise and lower the lift axle.

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   • Wheelbase= inches from center of steer axle to center of rear most axle.

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6. Double check your weight info – it’s up to 20k/axel and 34000 per tandem axel group. In my case I can run up to 19,000 steer 17,000 per axel in drive group and 19,000 per axel in my split axel trailer group (more than 10′ between axels)

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   • Your right on federal highways. States have their own steer tire weight limits

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7. I just wanted to add some information about the legal weight of a semi truck:

   In the US:

   There are one set of rules that are set by the US Federal government and they say that for highways that are federally funded (interstates and some other bigger roads) the minimum weight that states HAVE TO allow is 80,000 lbs.

   States cannot set the limit on interstates lower than 80,000 lbs, but they can set lower limits on state highways. However, there is a catch.. if a state had a higher weight limit in place before this federal law was passed (Surface Transportation Assistance Act of 1982 (STAA)) the state can still allow trucks heavier than the 80,000 lbs limit. The state with the highest weight limits by far is Michigan. The highest grossing truck without a permit in Michigan can top out at 151,400 lbs! With 8 axles on the trailer! Without a permit! Usually these trucks carry loads of raw steel between steel mills and factories.

   In Canada, most of the country allows much higher weights than in the US (but not as high as Michigan). Each province sets their own weight limits independently. A typical combination in Canada is a tandem drive tractor with a tri-axle trailer. This is like the typical 18 wheeler with an extra axle on the trailer (22 tires). Weights vary across the country but they are usually around 110,000 lbs. The second usual combination that is used across Canada is the B-Train. It is a tandem drive tractor pulling a trailer with three axles, and attached to this trailer is a second trailer with two axles. Across Canada, the B-Train weight limit is 139,700 lbs (63,500 kgs).

   Paul at http://www.bigtruckguide.com

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   • B-trains actually have 2 axles (tandem in the center. The combination you are referring to is actually a Super-B train.

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8. Do trucks have a legal right to travel on a federally funded highway even if a city or other municipality posts signs prohibiting trucks

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9. I see lots of seni trailers with skirting under the trailer, what does the skirting do?

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   • They cut down on wind resistance, improving the aerodynamics and fuel efficiency of the eighteen wheeler. Trailer skirts can increase MPG by a few percentage points, which saves thousands of dollar per year in fuel costs.

     Early versions were rigid and prone to breaking when hit by debris on the highway at 65mph. I’ve heard that some newer versions have flexibility built in and are able to withstand the daily abuse.

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10. Can I get the overall length of a typical U.S. Wal-Mart semi tractor trailer? There’s would no indication of any sleeper accommodation to the tractor, so I am guessing this would be closer to 70 than 80 feet.

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    • Linda,,, The overall length of a Wal-Mart trailer, from back door to the nose, is 53ft. and the length of the truck at the point of trailer nose to the front of truck is about 11 to 12 feet and this is a sleeper truck. So the overall length of your average Wal-Mart truck is 64-65 feet long and also the legal width of any truck is 8 to 8.5 feet, anything over that wide requires an oversize permit.

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11. What is the net weight of a tractor trailer truck? How much does a unloaded tractor trailer weigh

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    • My guess is most combinations are 2-4,000 lbs lighter. My tractor is heavier than most, not all. If I remember right my tractor, alone, is around 22,500 with full tanks of fuel.

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    • “most” trailers can have a load weight put in the that weighs “about” 43000 lbs, so take 43000 – 80000 gross weight and that give you a truck/trailer combo weights empty “about” 37000 lbs

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      • Trucks weigh 31,000 lbs. +/- with empty 53′ trailer. they max out at 80,000 Lbs., But can carry more with more axles and permits.

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12. Recently, as I was driving for 3 hours on Interstate 5 in Northern California, I logged the manufacturer of every semi truck I passed. Here is the breakdown: FreightLiner – 40 Volvo – 18 Peterbilt – 17 Kenworth – 13 International – 3 Mack – 2

    Is this an approximately fair representation of market share? Would it be noticeably different, say, on the east coast? People sometimes say “built like a Mack truck!” – what happened to that brand?

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    • There are way more Internationals Macks where I live and there are lots of Western Stars and Sterlings too

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    • Mack is known for dump trucks, not semis. There is a reason you only saw 2. Buy a Freightliner. There is a reason you saw 40.

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    • I drove for UPS, I drove a Mack for years, and loved it!

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    • The company I work for has 700 drivers and over 550 trucks, of which 80% are Macks. It all depends where you are,

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13. how many gallons of diesel fuel does an 18 wheeler hold on both sides thanks

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    • generally 45-50 gallons, varies by year and manufacterer

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      • per side*

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    • Our Volvo holds a total amount of 247 gallons of fuel, 123 gallons with some change per tank but hubby and I run a 2016 Volvo 730 ( has sleeper berth ) not a smaller day cab. Were OTR long haul Drivers.

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14. I think Mack and Volvo merged.

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15. One thing not covered was truck brakes….you often hear people say the truck should be able to stop like a car because it has 18 brakes…lol show me 18 brakes on my truck and trailer….. The last time i checked my truck n trailer has 5 axles and that equals 10 brakes at 1 set of brakes per wheel location…that’s 5 on each side of the vehicle 1 or wheel location of which there are 10

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16. I guess my truck is a little heavy then. Fully fueled, with a 53′ dry van, I weigh 36000. The wheelbase is 300″. I hold 270 gallons of fuel and get between 4 to 5.5 mpg depending on what part of the country I’m strolling.

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17. I’m a car Hauler and I have heard that car haulers are allowed to be over 13,6 height. Is this correct? And if so what is the heighth?

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18. What is the average hight of main freeway’s and highway’s bridges, overpasses, and tunnels? Is it different in Canada?

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19. How much does a semi rig tire and wheel weigh? The wheel diameter is 22.”

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20. Most truckers I have met over the years are intelligent, polite and helpful, where does this community stand on violations of small town bylaws regarding the garaging, parking and operations of their semi’s in a residential neighborhood where they also reside? One neighbor is a trucker and does give a hoot about fumes, idals his truck for over the law’s amount of time. Pulls out with high beam head lights on waking neighbors at 4 or 5 AM. I respect your profession an feel people like him are not suitable to be a professional truck driver.

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21. May want to look at article on legal Canadian axle weights. Legal tandem weight in Canada is 17000kgs.

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22. What is the maximum legal weightload of 18 Wheeler truck with 2 axle & 3 axle in US and Canada?

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23. How much does a semi-truck tire weigh?

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24. Can you tell me how long it takes for a 70-80 semi to go from a complete stop to moving (like @ a stop light).

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    • That totally depends on the weight of the unit, the power of the engine, and the driver. \generally though, much longer than a car.

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25. Canadian axle weights are wrong….5500kg steers 17000kg drives 17000kg trailer ( tandem ) 24000kg ( tri) Please fix this….

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26. Floating gears is bad for the transmission cause everytime you pull it out of gear you take a little metal off the teeth any driver or mechanic that says its ok doesnt know what he is talking about

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27. Does anyone know the percentage of solo women drivers today? When I ran all 48 and Canada back in the 1980’s, a safety director told me that only nine percent of drivers were women and, of that nine, only three percent ran solo. I was one of the three percent. Back then, 53-foot trailers were not allowed on the dirty side except on the interstates. I pulled a few in my day, mostly out west, but now they’re standard. There were no computers, no cell phones, no automatic transmissions, and company drivers did NOT have jake brakes. You either knew how to handle a truck or you didn’t. Things have really changed!

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28. It takes a special license (CDL), and special skills to operate an 18 wheeler, skills learned over time. You can’t just hop in an 18 wheeler and expect to know what you are doing. It takes a special kind of person to drive an 18 wheeler.

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29. Air brakes. I hope nothing breaks.

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30. If you have a apu installed you are allowed 800 pounds over or 80800 gross. That is the weight of the apu. One thing I have noticed this winter if you get uncomfortable while driving with the weather or actions of traffic park it. Your dispatcher and company may try to get you to continue but the choice is yours.

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32. Alot of knowledge I just read and useful as well. But one thing I didn’t find or read about was this; As a truck driver am I allowed to add a motorcycle trailer on the end of my semi trailer to take a motorcycle back home that I purchased during my 7 week of being on the road?

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