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How are truck-tractors' GVWR calculated?

Discussion in 'Trucks' started by texascadillac42, Apr 5, 2008.

  1. texascadillac42

    texascadillac42 Well-Known Member

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    I recently drove a truck-tractor from a fleet company with a 20k front axle, and 38k rears. The GVWR of the tractor was only 23,587. How does this work out? And how can the EXACT same truck with a dump body instead of a 5th wheel hitch be rated with a GVWR of 80k? Are the tractors rated at a lower weight because the trailer gets them to 80k GCWR, and insurance and plates would be cheaper? Thanks for any help.
     
  2. jimmyjack

    jimmyjack Senior Member

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    in RI a truck with those specs as a dump truck would be good for 58000, most tandem and tri axles that i've seen at home don't have those light rears like a tractor. they normally have 46 or like most macks use 58s, example the mack ten wheeler i drove had a 18 front and 58 rears on11.00x24stires so it had a 76000gvw, and the tri axle i later drove had 14 front 20 pusher and 44 rears that one had a 76650gvw. most people dont use truck that were tractors converted to dumps cause of the light rear and high gearing

    now i know most states out side of new england use the bridge law which i dont know much about but it as to do with the distance between axlesnot axle rating ,but someone else will most likely staighten me out on that:beatsme
     
  3. texascadillac42

    texascadillac42 Well-Known Member

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    Several of the tractors that Ive driven were only used for local, heavy equipment moving, so they have 58k rears as you described. I just dont understand how with the axle weight ratings as they are, the GVW is ridiculously low.
     
  4. jimmyjack

    jimmyjack Senior Member

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    that 23000 sounds more like the tare weight of the tractor not the gross
     
  5. texascadillac42

    texascadillac42 Well-Known Member

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    By tare, I assume you mean unloaded weight. I think these fleet trucks, which are day cabs are around 15 or 16. Pretty light really.
     
  6. BIGDAN315

    BIGDAN315 Well-Known Member

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    I believe the formula they use here in NY is as fallows, rear tandom axles ragardless of how much they are rated for can only cary 34000 lbs. So you add 1000 lbs for every foot of wheel base your truck has and thats your max GVW without a permit. So short tractors are limited.
     
  7. ben46a

    ben46a Senior Member

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    I tried several thing but cant figure out how that number was arrived at. Almost sounded like its in Kilograms instead of pounds. Up here were allowed up to 38,000 lbs on a tandem cluster and up to 17,000 lbs on the steer, depending on factory weight ratings of course, which are not to be exceeded.

    Actually, i bet that number is KGs, which would be 52000 lbs, allowing your 38K on rear and 14K on the steer, which is how most places run weights on tractors.
     
  8. LowBoy

    LowBoy Senior Member

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    That actually sounds a little heavy for a tare weight on a tractor with 38's.

    Wonder what the tractor was intended for originally? 38's with a 20K front is also kind of a morphadite.
     
  9. D3B Dave

    D3B Dave Active Member

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    This thread brings up a question I have had for some time. When an OEM builds a truck it is given GVWR, on a door sticker by Federal Law. Keep in mind I am talking about the OEM rating of the truck, not what the truck can weight based on wheel base, or number of axles, by any State Law.
    We have all seen dump trucks that have had one, two, three, or more "drop axles" or "strong arm axles" installed so the truck can legally carry more weight based on State Law. In doing so it did not change the GVWR assigned to the truck from the OEM.
    Is this safe?
    Is this smart?
    My 9300 Int. came from the Factory as a tri-axle dump truck with a GVWR of 62,350. The wheel base would allow for a 4th axle, thou I will never install it.
    It sure seems like a way to "Feed" a Lawyer, if anything ever happened, something I hate doing.
     
  10. 95zIV

    95zIV Senior Member

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    The bridge formula

    Here's a explanation of the bridge formula, it also has a chart to show the weights. When it comes to weights and what you're actually allowed with what I've seen for info and such. Generally you are allowed 600lbs per inch of width on a tire. If anyone is looking for a pretty decent reference that you can keep in your truck, the truckers road atlases that I've seen have the charts and info on all the states just inside the front cover.


    http://www.mapbooks4u.com/page/163663/
    Rand McNally: Road/Street, Motor Carriers/Truckers Atlases & Driver' s Guides Discounted! (866) 896-MAPS


    http://en.wikipedia.org/wiki/Federal_Bridge_Gross_Weight_Formula
    Federal Bridge Gross Weight Formula - Wikipedia, the free encyclopedia
     
  11. GaryKelley

    GaryKelley Well-Known Member

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    There seems to be some confustion here. Often times, the rating of the REAR axles ie; 44k, 56k, 38k etc. has NOTHING to do with the GVWR of the vehicle. These numbers are assigned by the manufacturer of the rear ends, NOT the vehicle manufacturer. The higher the number, the sronger the component. Whether or not you could have a vehicle with a GVWR higher than the weight rating of the rear end is not easy to identify. I have seen semi-tractors of GCVWR of 80K and have light weight SQHD rears rated at 36K. The additional weight is achieved with the towed vehicles (trailers), interstate rules allow 34K for tandem axles and 20K for singles axles 12.5K for steering axles.
    The way the rules are appled is very subjective, one state using one set of standards, and another state using a different. However all most all states use the guidelines of TIRE ratings and axle ratings to establish base line weights.
    Confused yet? Nike and Addidas dont have weight ratings..