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

[bluemoonKY]

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.

 

[etudiant]

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.

 

[Averagesupernova]

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.

 

[Ranger Mike]

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.

 

[Baluncore]

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.

 

[jack action]

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.

 

[Jupiter6]

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.

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.

 

[wyocoyote]

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.

 

[Ketch22]

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.

 

[cjl]

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.

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.

 

[Ketch22]

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.

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.

 

[Off Grid and Farming]

Hi, which arrangement would be better for off road carrying materials around, ploughing and winching? Would dual wheels still be better?

 

[Baluncore]

Hi, which arrangement would be better for off road carrying materials around, ploughing and winching? Would dual wheels still be better?

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.

 

[Ranger Mike]

ifin you want maximum traction..get dually with 4wd..diesel preferred

 

[Jon smith]

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

 

[Work Hard Play Hard]

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.

 

[RonL]

When tires were single and skinny, 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

 

[JBA]

As for off road performance, I have yet to see a dually Baja or Dakar rally, or expedition vehicle so equipped.

 

[Ranger Mike]

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

 

[RogueOne]

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)

 

[CharlesS]

Trucks with dual wheels are about a foot wider compared to single wheel counterparts. The increased width effectively lowers the center of gravity of the whole vehicle. When hauling a top heavy load such as a slide-in camper or towing a large trailer this becomes apparent as increased stability.

 

[Baluncore]

Welcome to PF.

Trucks with dual wheels are about a foot wider compared to single wheel counterparts.

The over-all width and height of a vehicle is regulated, the length of the axle is not. Trucks are built to meet the width regulations.

Where dual tyres are fitted in place of a single tyre, the two wheel rims used are offset and the tyres fitted are still limited by body clearance and over-all width. So there can be no improvement in stability for road registered vehicles, without exceeding the width regulations.

Since the suspension is attached to the axle at the same design points, the truck body will lean in the same way no matter what wheel configuration is fitted. Overturning will occur at the same point since it is the hardness of the suspension that decides the lean and the movement of the centre of mass.

 

[jack action]

Where dual tyres are fitted in place of a single tyre, the two wheel rims used are offset and the tyres fitted are still limited by body clearance and over-all width.

I think he meant comparing these designs:

Overturning will occur at the same point since it is the hardness of the suspension that decides the lean and the movement of the centre of mass.

Actually the main characteristics for overturning is the height of the center of gravity and the track width as shown in the figure below. Though, a softer suspension will generally lower the maximum lateral acceleration before overturning occurs.

 

[CharlesS]

In the US vehicles are limited to 8 feet wide in some states and 8.5 feet wide in others. Cab and chassis models of domestic trucks have the same axle width as a single wheel truck, however they use a reversed wheel on the inside dual with another reversed wheel opposite on the outside dual. A single wheel version tracks almost center of midpoint of the dual wheels on these models. Often a cab and chassis model will be fitted with a flat bed body. On a dually pick-up truck which has a factory pick up bed with dually fenders adapted to the outside quarter panels, the width of the bed between the fender wells remains at 4 feet, the same as a single wheel model of the same truck. The axle housing is wider spacing the wheels further apart, and the inside dual rides the same distance from the frame and the inside wheel well maintaining a 4 foot clearance between the wheel wells exactly like a single wheel model. The minimum 4 feet width between the inner fenders is a standard for US built pick-ups. The standard size for plywood is 4 x 8. Slide-in campers have a 4 foot width at the base where they sit in the bed. 5th wheel hitches are built to place between 4 foot width fenders. A standard shipping pallet is approx 4 feet wide. The outside duals widen the trucks width by the width of the tire and wheel, making the entire width of the truck at nearly 8 feet compared to a width of close to 7 feet on a single wheel version of the same truck. I am using the terms close to because different models vary somewhat within a range. The width of the outside duals matches the width of most cargo trailers, many trailer-able boats, and RV's. The inside dual tracks the same as the front wheels. Springs are mounted in the same location, however dual wheel trucks have a higher GVW compared to single wheel counter-parts and have HD springs which limit body roll. Add to that most dual wheel pick-ups are equipped for RV use and a torsional sway bar is included. Increased spring tension and sway bars reduce body roll. The increased width of the wheel tracking effectively lowers the center of gravity for the overall load.

 

[Baluncore]

Though, a softer suspension will generally lower the maximum lateral acceleration before overturning occurs.

Softer suspension effectively narrows the track width. The effect is most pronounced with loads that have a high centre of mass.

The term “Truck” needs to be better defined, or more carefully used.

There is no question that widening the vehicle track will increase stability. That may be possible with pick-up trucks as they are not normally 8 feet wide, but it is not possible with semi-trailers used in the trucking business as they are already 8 feet, (or 2.5 metre wide).

Widening the track while maintaining the same wheel base reduces directional stability during acceleration and braking if ABS is not fitted. That may lead to overturning if directional stability is not maintained.

 

[CharlesS]

Very true! There is not much one can do to change the width of a semi.

We currently own an F-150, F-250, and an F-350 dually. All three "trucks" have crew cabs and are the longer of the wheel bases offered for each model. Each one has ABS, are all respond well in a panic braking situation. We haul a 2800 lb slide in camper on the dually and tow either a 24 foot enclosed race car trailer or a 22 foot sport boat behind. The differences between the road manners comparing the F-250 and the F-350 dually with the same load are obvious. The F-250 is almost the same truck with the same engine and running gear. The major differences between the two trucks are spring rates and the dual wheels on the F-350. A previous "truck" that we owned was an older Chevy CK-30 crew cab dually 4x4. That "truck" did not have ABS, and could be scary in a panic stop especially with no cargo in the bed. The four dual wheels would lock up quickly and the "truck" would slide easily even on dry roads. Eventually I installed a 120V/240V generator in the bed of the truck which added roughly 1000 lbs weight to the bed. A 1000 lbs is not much weight for a "truck" with a 10K GVW, however the added weight close to the rear axle did make a difference in the traction during a panic stop situation. When we towed our 10K 5th wheel travel trailer, the 2700 lbs tongue weight on the bed mounted hitch placed four inches in front of the rear axle planted the four tires firmly on the pavement, making a panic stop a lot less scary. The F-250 single wheel truck is more capable as an off roader or on snow covered/ice covered roads compared to the dual wheeled F-350.

 

[DaveC426913]

Road surfaces have a limited strength, so a bigger tire contact surface is needed to keep the stress within legal limits.

You know, I was well into my 40s before I had the eureka moment that the extra wheels on trucks aren't there to protect the truck.

 

[CharlesS]

The event that convinced me to upgrade to a dual wheel truck happened in the 1977. We owned a 1972 Chevy C-20 Custom Camper Special with a 10 foot slide-in camper on it. Only had one kid at the time, and crew cab trucks weren't as common. We had a trip planned and the tires on the truck needed replacement. I purchased Michelin tires for extra safety because no one wants to have a blow-out with a heavy camper on a truck. The truck had split rims so tubes were required. The installer used bias tubes with the radial tires. The first tube failed as we were coming across a long bridge over a waterway. A rear tire blew out almost causing the truck to flip over the side of the bridge into the water a 100 feet below. The truck actually ended up on the sidewalk up against the guard rail with the camper hanging over the rail. No one was injured. Fast foreword to the 1980's. Hauling a much larger slide in camper on a one ton crew cab dually. Three kids in the back seat playing Pac-Man on the Nintendo. Pulled into a gas station to fill up. On visual inspection, one of the inside dual's was flat. Finished filling up the fuel tank, then pulled around to the service area where they removed the tire and found a small hole. They hole was patched, tire replaced, and we were on our way in 45 minutes. Also, the additional stability provided by dual wheels when hauling a heavy load is priceless. Again, it depends on the type of driving one does and what sort of load they carry on the truck.

 

[Andy SV]

Until you lift the inside wheel of a truck you get minimal benefit from a wide wheel base. Until then the stability of the truck is determined by the geometry of your suspension and the stiffness of your sway bar.
One big tire provides superior performance absorbing punishment before failure
A set of tires provides superior performance after a failure
It's up to you to decide

 

[RogueOne]

Until you lift the inside wheel of a truck you get minimal benefit from a wide wheel base. Until then the stability of the truck is determined by the geometry of your suspension and the stiffness of your sway bar.

Load from the trailer is distributed more evenly between tires as the wheelbase increases. This means lower slip angles on turns, up hills, or stopping. Suspension dampening as well as wheelbase are big factors in stability.

There is a lot of complexity in tire engineering, but there are 3 big things that I know of that make dual wheels the choice over singular wheels with large tires.

1- Rim Load capacity
2- Contact patch size and Vertical load's relationship with traction
3- CostThe "what if I get a flat tire" scenario is not the central topic here. If it were, then you could justify dual wheels on the front of the truck as well. You could use that premise to justify dual wheels on every car on the road today. Motorcycles would absolutely have dual wheels front and back!
If safety is the primary reason for dual wheels, why do dump trucks and semis have dual axles as well? This is about load distribution.

I've already posted this once in this thread, but apparently nobody is reading it. Here it is again
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)

 

[DCar Guy]

Off topic question i hope one of the truck guys may know. I think the answer is yes, but, do all dually's use a Full Floating Axle over a Semi-Floating Axle?

 

[Averagesupernova]

Off topic question i hope one of the truck guys may know. I think the answer is yes, but, do all dually's use a Full Floating Axle over a Semi-Floating Axle?

Based on my experience I would say yes. Haven't seen a truck with duals that wasn't floating.