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noteven's avatar
noteven
Explorer III
Mar 09, 2015

Pickup truck tow vehicle stability tests

Always lots of anecdotal statements on rv.net around dual wheel vs single rear wheel "stability".

Anyone have any links that point to actual testing results under controlled conditions?
Tow Vehicles

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  • BenK's avatar
    BenK
    Explorer
    Mar 10, 2015
    Why my Suburban has -1.5" offset alloys....stock is +1.5", so the net for both
    sides is an increase in track of 6"...plus that my rims are 10" with stock at 6.5"

    Means another 3.5" wider track

    Plus my tires are 10mm wider, so 10mm wider track

    All adds up to about 10.5" wider than stock track, front and rear

    A dually has an even wider track






    It is not any one aspect, but all of them in concert that matters...AKA in context


    If this guys car had a narrower track...think he could do this with the
    exact same car?...or would he roll over?

    This is part of what a dually does better than a single with a narrower
    track...managing that 'push' and 'sway' from the trailer

    leanbar sidewall aspectratio track
  • transamz9's avatar
    transamz9
    Explorer
    Mar 10, 2015
    Bedlam wrote:
    transamz9 wrote:
    So what everyone is saying is that a 1999 DRW 3500 is going to be way more stable than a 2015 SRW 3500? DREAM ON! Two extra tires don't make the difference people. I drive them both daily. I have pull the same loads with both and there ain't as much difference if they are both with-in their capacities. When you go from a SRW truck to a 5 year newer DRW truck then yes it's going to seem night and day difference.

    Although the the wider stance helps slightly in stability, the fact that the axle is sprung to the frame at the same width between SRW and DRW creating a pivot point tells me this is not the answer. I feel it has to do with the spring rates of the leaf pack and the torsion strength of the stabilizer bars that gives the DRW a more steady feel over the SRW. Unless side winds were so great that lateral traction was compromised with a SRW, I cannot see how a wider footprint will help.

    Matching the track of the tow vehicle to the trailer is important on worn highways where the wheels will hunt for the depressions, but now we're talking about matching vehicle width to road conditions rather than stability differences between vehicles.

    I will wag that if you took identical trucks with nothing different between the two other than a SRW and DRW rear axle, you would be hard pressed to differentiate between the two. If you have a DRW, an easy test to prove this is to remove the the outside wheels and run with only the inners.


    :W

    You can't just remove the outer wheel and tire though, You have to put a normal SRW offset wheel on with a matching SRW size tire.
  • Bedlam's avatar
    Bedlam
    Moderator
    Mar 10, 2015
    I have to agree that once off pavement, you would notice the difference between SRW and DRW. There's many reasons you see most heavy off-trucks with super singles instead of doubled up wheels.

    I haven't seen anyone argue about using different wheel offsets yet other than those that haul close to their limit and worry about the additional leverage of greater outside offsets...
  • IdaD's avatar
    IdaD
    Explorer
    Mar 10, 2015
    Bedlam wrote:

    I will wag that if you took identical trucks with nothing different between the two other than a SRW and DRW rear axle, you would be hard pressed to differentiate between the two.


    Put both trucks on a narrow and rocky forest service road in the mountains and they'd be pretty easy to differentiate.

    A DRW truck is a unitasker. Great for highway or interstate towing. Worse than SRW for literally everything else.
  • Bedlam's avatar
    Bedlam
    Moderator
    Mar 10, 2015
    transamz9 wrote:
    So what everyone is saying is that a 1999 DRW 3500 is going to be way more stable than a 2015 SRW 3500? DREAM ON! Two extra tires don't make the difference people. I drive them both daily. I have pull the same loads with both and there ain't as much difference if they are both with-in their capacities. When you go from a SRW truck to a 5 year newer DRW truck then yes it's going to seem night and day difference.

    Although the the wider stance helps slightly in stability, the fact that the axle is sprung to the frame at the same width between SRW and DRW creating a pivot point tells me this is not the answer. I feel it has to do with the spring rates of the leaf pack and the torsion strength of the stabilizer bars that gives the DRW a more steady feel over the SRW. Unless side winds were so great that lateral traction was compromised with a SRW, I cannot see how a wider footprint will help.

    Matching the track of the tow vehicle to the trailer is important on worn highways where the wheels will hunt for the depressions, but now we're talking about matching vehicle width to road conditions rather than stability differences between vehicles.

    I will wag that if you took identical trucks with nothing different between the two other than a SRW and DRW rear axle, you would be hard pressed to differentiate between the two. If you have a DRW, an easy test to prove this is to remove the the outside wheels and run with only the inners.
  • noteven's avatar
    noteven
    Explorer III
    Mar 10, 2015
    bmet2000 wrote:
    On the BMET scale, a dually is 72.7% more stable...


    Now we are getting somewhere :)

    How did you arrive at your results :):)
  • noteven's avatar
    noteven
    Explorer III
    Mar 10, 2015
    In the absence of controlled test results then these examples are acceptable?

    Double stable?:





    single wheel, defaults to unstable?:




    Stable:



    Wheel and tire change (19.5's on the left):



    Track width is the same, but now defaults to not stable?:



    Also single rear tires - therefore unstable?

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