Advantages of a spread axle trailer?

Discussion in 'Questions To Truckers From The General Public' started by Bobg, Feb 12, 2009.

  1. Winchester Magnum

    Winchester Magnum Road Train Member

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    Les, you kinda lost me there. I use my dumps at every turn I make, so to minimize tire scrub --- in addition to backing into those holes made for 6 wheelers.

    What do ya mean by you've seen "what dumps do to others"??
     
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  3. The_possum

    The_possum Bobtail Member

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    The other nice thing about spreads, is that in some instances, with overweight permits you are allowed WAY more weight on them.. For instance, in WI, with a recycling overweight permit, I was allowed 42K on tandems, and 50K on a spread, but only 55K on tridems.. So depending on which trailer I pulled I was either legal to 102K or 109K.

    As far as the handling and ride, I'll take a spread any day of the week.. even for backing them up too.. Now if you get into an older walking beam spread, they can be a bit interesting backing over uneven ground at times, especially when all the bushings are shot..

    I think most people would pee their pants if they seen what our 11 axle log trucks, gravel trains, or B train setups look like.. legal to 164K pounds.. and 18K on the steers..
     
  4. ironpony

    ironpony Road Train Member

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    No, I see what your getting at. Same deal as working a tandem all the way back to get in, then sliding it forward to tighten the radius.

    Actually no. The company I pull for provides the trailers - so it's their call. Can't say I appreciate seeing "tire scrub" when trying to turn those things tight. The other real disadvantage I see is not being able to adjust the axle position to maximize your fuel economy. But that's me! As long as ya'll are happy with the things!
     
  5. Bobg

    Bobg Bobtail Member

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    Thanks guys, that's what I wanted to know. I don't see many of them in our area, but we get mostly farm semi's with grain trailers.

    Bob
     
  6. lv gn

    lv gn Heavy Load Member

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    can you explain that just a little? i pull tankers and cant slide tadems. where do you put the axles for the best mpg? thanks.
     
  7. ironpony

    ironpony Road Train Member

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    If you think about it, what the engine is doing is overcoming the resistance to the tires rolling caused by friction. Simple physics... that force is just the weight times the rolling friction coefficient. So without knowing what the friction coefficient is, it's roughly a fraction of the weight on the wheels.

    What you want is the least force of resistance to overcome, so the engine uses the least amount of fuel to get the load down the road. So roughly, if you have about equal weight on the drives and tandems you should be there - a lot more weight on one set or the other will dominate the relationship. My fuel log shows that an equal weight on each set is about where I get the best mileage... in practice it seems like it works a little better if there's a little more weight on the drives.

    So you weigh-out the trailer at the CAT scale or use the rite-weigh meters - hopefully calibrated properly - with the tandems set to a good guestimate of where things should be. Then, using your measured weight you figure where that equal point is and you slide the tandems to get about an equal weight distribution, with a little more on the drives. If the weight is equal somewhere between say the 9th and 10th hole... choose the 10th - puts a little more on the drives. Our newer Wabash trailers adjust the weight at a little more than 300 lbs per hole on the slider as long as you're close to start with. Seems like its not quite a linear relationship, the further you get away from the "equal point." Oh yeah... hole no. 1 is at the front end of the slider rail.

    I use... no. of holes to move = 0.5 x ((tandem wt - drive wt)/320)

    That yields a number like -2.4561 or 4.2967 - the whole number (-2 or 4) is the number of holes to adjust the slider from where the tandem was set when you weighed it. Negative means move it towards the cab, positive means move it away from the cab. Let's say you're in the 12th hole when you weigh, and you get -2.4561... 12 + (-2.4561) = 9.5439. Put it in the 10th hole.

    All things being equal, it depends on how the trailer is loaded too. The load I'm pulling now is heavier at nose so in the 4th hole I'm about 31k on the drives and 29k on the tandems... best I can get. The worst fuel mileage comes with the tandems set so you have a lot more weight on the back. Just because it's legal, doesn't mean it's efficient... it can be worth up to a mile per gallon in efficiency - that's why I'm happy with tandems on a slider. It's $$$'s into my pocket.

    This is another reason why CA sucks. The bridge law out there means I have to be in the 6th hole (with our trailers... your holeage may vary!) to make Ahnold and Company happy. Most of the time that means the back end of my trailer is way heavy, and I'm burning a lot more fuel to get it down the road.
     
    Last edited: Feb 14, 2009
  8. lv gn

    lv gn Heavy Load Member

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    LOL! about spit my coffee out on that one! thanks for taking the time to write that out!
     
  9. kd5drx

    kd5drx <strong>Master of Electronic Communications</stron

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    Oh my i have never heard that one explained before now i do know when running M/T i used to suck my front axle up on my spread to save tires and also got a little better fuel millage because of 4 less tire on the ground but equal weight causing better fuel millage please. Tire pressure has more influence than weight distro on fuel millage.
     
  10. heyns57

    heyns57 Road Train Member

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    "I think most people would pee their pants if they seen what our 11 axle log trucks, gravel trains, or B train setups look like.. legal to 164K pounds.. and 18K on the steers.."

    Several states permit more than the standard 5-axle, 80,000 lb rig. Michigan was "grandfathered in" with higher weights on the Interstate when the limit increased from 73,280 lbs. The older Michigan limit was 173,000 lbs on 13 axles.

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    Last edited: Feb 14, 2009
  11. Lilbit

    Lilbit Road Train Member

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    That's a lot of tires there!
     
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