Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automotive What is the advantage of having a dually truck vs. nondually?

  1. Mar 1, 2014 #1
    What is the advantage of having a daully truck vs a truck that just has one tire on each side of an axle? I mean, how is having four tires per axle better than having two tires per axle? There must be some advantage or there would be no reason for daully's.
     
  2. jcsd
  3. Mar 1, 2014 #2

    etudiant

    User Avatar
    Gold Member

    Road surfaces have a limited strength, so a bigger tire contact surface is needed to keep the stress within legal limits. It's very expensive to make a wide tire, so the cheap solution is to put two side by side.
    Just as an aside, road damage compounds as the 4rth power of the weight/surface, so that essentially all the road damage is done by heavy trucks. If fuel taxes were allocated on the basis of damage created, gasoline powered cars would be tax exempt, because the average American car, at 2000pounds/axle, is imperceptible in terms of road damage.
     
  4. Mar 2, 2014 #3

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    Redundancy is a very good reason. Some trucks are on the road now with one large tire in place of a set of duals. I am not a fan. A set of tandem axles on a semi-tractor/trailer have a max weight of about 34000 pounds. This weight is divided up 8 ways with duals. If one of these tires blow out there is a much better chance of keeping the truck under control compared to if a tire blows with only 3 left. A large wide tire that replaces a set of duals can be a lot of weight flopping around if it blows compared to a single tire from a set of duals.
     
  5. Mar 3, 2014 #4

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

    Having driven a race car hauler for over 40 years I have driven them all. Gas pick up truck, van, and diesel Single Rear Wheel drive Ford and Dodge Cummins dually diesel. By far the best set up for me is the Dual Rear Wheel drive (DRW) Dodge Cummins diesel dually with a 6 speed manual transmission. Personally I prefer the Cummins inline diesel to the current V8 diesels out of pure stump pulling torque but that is another thread. Dually are the only way to go if you are pulling a 5th wheel trailer. Once you get used to driving the wide dually you won’t even know you are pulling a trailer when towing. I love mine!


    Pros of dual wheels

    - Stabler if cross wind or tractor trailer going the other way on a two lane highway
    - In the 1 ton pickup range you can tow about an extra 1,000 lbs. Perfect for the 5th wheel trailer.
    - Duallies are safer during a blowout, assuming one tire doesn't take the other out.
    - I don’t have empirical data but I like the aerodynamics of air flow blending the air stream along the truck cab sides and washing off the dually wheel wells. Has to reduce drag somewhat. My guess is adds 2 MPG towing vs. SRW drive truck.


    Cons
    - A SRW has a much better ride, the front tires are bigger and give a better ride.
    - decreased gas mileage. My estimate is 2 MPG empty.
    - DRW only available in long bed version and 1 ton and up.
    - if parking anywhere other then pavement or gravel you may need 4 wheel drive if unloaded as traction when empty is very low. Serious problem here in Ohio.
    - obviously more difficult to find convenient parking spaces.
    - Dually is more expensive but so is a diesel.
    -If you drive a lot of secondary and country roads. The extra width requires greater precision in driving.
    - If you drive off road a lot. Ability to choose what type of tires all the way around matters to me (for 4wd especially)
    - If you are on the east coast some states are adopting stricter guidelines for over 10k rated trucks. Dually wheels are a dead giveaway for a police officer to wonder if you are commercial or "non-commercial driver driving a commercial vehicle"
    - IF you are considering fifth wheel operation, forget all the above.

    Bottom line is The advantage of a DRW is the stability while towing. Disadvantages include the rear of the truck being nearly 8ft wide and the 2 extra tires to purchase every time you need new tires. They also do a little worse on fuel because of the extra tires. It a bit better towing by 2 MPG but empty you will lose about 2 mpg.
     
    Last edited: Mar 3, 2014
  6. Mar 4, 2014 #5

    Baluncore

    User Avatar
    Science Advisor

    Dual wheels on a drive axle transmit the torque to the road through twice as many flexible sidewalls. That gives more efficient power transfer and a longer tyre life.
     
  7. Mar 14, 2014 #6

    jack action

    User Avatar
    Science Advisor
    Gold Member

    A single wider tire could also carry more load and have better traction, so I think the real advantages we have to look for is by comparing two narrow tires vs one wide tire:

    • Blow-out protection – if one of your rear tires gets a flat, the others will temporarily carry the load;
    • Hydroplaning resistance - the space between the 2 tires gives an exit for the water, snow and mud, thus reducing the chance of hydroplaning.

    «Twin-tires» for cars were introduced on the market in the 80's, but they never caught on despite better performance. They supposedly run 20%-30% cooler and reduce hydroplaning by 80%. The only draw back seem to be a diminution in confort.

    Still some info the net:

    A good idea at the time: Twin tyres
    Drivers Do a Double Take as Two-Tire-Wheels Roll In : Roadability and Safety Stressed
    TWIN TIRES—- THEY'RE BACK: NEW FIRM TO MARKET SYSTEM IN U.S.

    VL_Beach.jpg
     
  8. Mar 15, 2014 #7
    In an ideal world, a 1" wide tire would work just fine. Asphalt is an imperfect surface, so you try to make up those gaps by getting more rubber out there transmitting your engine work to the road. There is a point of diminishing returns there though as far HP and tire/wheel combos.

    Pro street Mickey Thompson ET radials still do not have the spread of a dually footprint. It's much easier for a tire manufacturer to make a tire that can be used once or doubled, rather than one wide tire or one thin tire.


    Keep in mind, the tire business people grew with the automotive companies. They're there to make money.
     
  9. May 23, 2015 #8
    I wish I were better versed in the physics of dually versus single rear wheel (SRW). I am just a guy who drives dually full size pickups occasionally on and off road.
    I know many tractor trailers are switching to "super singles" (very wide tires as wide as a pair of duallies) and the reason is: better fuel efficiency.
    an off road disadvantage: getting a rock stuck in between the two tires can be mighty hard to get unstuck. and its sure hella harder to change the inner wheel when needed.
    I am unsure as to whether the super singers are more fuel efficient due to weight or traction, probably both.
     
  10. May 29, 2015 #9
    Couple of other things on both side of the fence. In most states of USA the weight is limited to 20,000 lb per axle and 18,000 lb per axle for anything within 7 feet of another axle. This must be evenly divided between the wheels. There is also often a limit of 800 lbs per rim inch width. Looking further:
    For a single tire to carry 10,000 lbs takes and incredibly strong ( 5,000 lbs per ) sidewall. These tires are really stiff to ride on and have a increased rolling resistance. (only when used on rough surfaces, when on polished hard surface it reverses). The softer sidewalls (2,500 lbs per) are much easier to roll. This must be balanced with the reduced rolling resistance of a broad Radial tire.
    Additionally of consideration is the overall width of the tire. If a tire drives straight forward with no turns it is low in resistance. As you turn the inside edge of the tire moves about a lesser distance than the outside due to the radius difference. This forces one edge to skid in relation to the other. The result is increased resistance and wear. Singles have a narrower overall width thus reduced resistance. Duals have higher wear due to increased skidding but reduced cupping as the lateral shift is split between two tires.

    So in the end Duals give more redundancy and lower resistance in straight lines. They do however have an increased operating cost. Singles offer reduced operating costs due to lower wear. but they require more robust gear to resist forces in a turn.

    This all is at the high end of big rigs at the limit of the public roads. As the vehicle gets smaller and further from the limits the differences are more subtle. For a "Dually pickup" the increased redundancy, reduced tire wear, and less robust ( read as lighter and thus more efficient) choice makes more sense.
     
  11. May 31, 2015 #10

    cjl

    User Avatar

    I was under the impression that large trucks were going to extra wide singles (to replace duals) because the singles had lower rolling resistance, while the duals had the advantage of redundancy and being less specialized.
     
  12. May 31, 2015 #11
    That would be a true statement. While each of the tires due to the width and aspect ratio has a higher Lb/in2 which offers a reduced rolling resistance this is so marginal that the increased friction when off of a straight line for duels as opposed to the large singles more than offsets the advantage. Since the only place you drive a dead straight line is on a salt flat it is more economical to run a single. Another advantage is that there are still a fair amount of the tires for duals that are bias ply. while virtually all of the singles are radial. Several of the trucking companies are still doing there own in house studies. This is why you periodically see rigs with lines painted radially on the sidewalls.

    Another conundrum that is seen is quarry rigs and dump trucks that are used on dirt roads. The larger more heavily loaded tires give a marked improvement in ride and driving over small obstacles. But the harsh environment really drives the use of duals for redundancy.
     
  13. Aug 20, 2016 #12
    Hi, which arrangement would be better for off road carrying materials around, ploughing and winching? Would dual wheels still be better?
     
  14. Aug 20, 2016 #13

    Baluncore

    User Avatar
    Science Advisor

    The answer is probably to use a single tyre of the appropriate design for the ground conditions.
    Rocks may get stuck between dual tyres.
    Sharp rocks do more damage to balloon tyres than narrower dual tyres.
    Tractor tyres have tread that sweeps the damp surface clear as they spin.
    Ploughing is most economical when there is some wheel slip. Do you need less ground pressure? or more traction?
    You can expect dual tyres on a tractor to pump soil and rocks into the gap between tyres.
     
  15. Aug 20, 2016 #14

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

    ifin you want maximum traction..get dually with 4wd..diesel preferred
     
  16. Mar 4, 2017 #15
    Ok so what I'm looking at is a dodge cummins (used) with a manual and either a flatbed or a hydro spike bed (for moving hay bales) with a manual transmission but the only ones srw are either really expensive or have 300K without any suspension or steering parts replaced and flat or spike beds are expensive not pre-installed and I need to be able to go into a back field and be able to pull a trailer with 4-5 hay bales on it but the thing is I also want to be able to go mudding and off-road because I'm a teen in a farmer community and so will getting a dually effect that please help and thanks
     
  17. Mar 4, 2017 #16
    I've only owned one and only then because it was a truck at the right time at the right price. It was noisy and threw rain everywhere. It was a 60's truck.
     
  18. Mar 4, 2017 #17

    RonL

    User Avatar
    Gold Member

    When tires were single and skinny, :cool: I have a single tire pickup and a dually F-350, could not follow this truck........



    Guess I'm just a modern day fat tire wimp :eek: :biggrin:
     
  19. Mar 4, 2017 #18

    JBA

    User Avatar

    As for off road performance, I have yet to see a dually Baja or Dakar rally, or expedition vehicle so equipped.
     
  20. Mar 6, 2017 #19

    Ranger Mike

    User Avatar
    Science Advisor
    Gold Member

    jon, do not buy a rear wheel drive dually for the field. it is too ass end light !. buy 4 wheel drive dually or 4 wheel drive period. the my dodge cummins can not pull the hat off your head if no rear end weight like my race car trailer. bur on asphalt when hooked to the trailer..NOTHING tows like a diesel
     
  21. Mar 6, 2017 #20
    Duallies get better traction when you have a lot of weight on the truck's rear axle. Tongue weight is what matters with duallies. Trailer's weight and trailer's tongue-weight that it applies to your hitch are not the same thing. It depends on where the trailer's axles are, relative to the trailer's center of gravity. Think fulcrum.

    The friction coefficient for tires in the real world decreases as vertical load on the tire increases. So adding more vertical to a tire does not linearly increase the amount of traction that the tire will provide. It does, however, increase the tractive effort needed to accelerate or stop the system. The best way to increase traction under heavy loads is to increase the contact patch of the tire. The cheapest way to do that is to add another tire.

    https://en.wikipedia.org/wiki/Tire_load_sensitivity
    https://en.wikipedia.org/wiki/Tire_load_sensitivity#/media/File:Tire_Load_Sensitivity.png https://en.wikipedia.org/wiki/Tire_load_sensitivity#/media/File:Tire_Load_Sensitivity.png

    https://en.wikipedia.org/wiki/Slip_(vehicle_dynamics)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: What is the advantage of having a dually truck vs. nondually?
  1. Mechanical Advantage (Replies: 1)

Loading...