The Evolution of Truck Wheels: Duals or Super Singles?
The design of semi trucks has undergone numerous changes over the years, with one of the most notable being the choice between dual wheels and single large wheels. This decision is driven by a variety of factors including weight distribution, traction, load capacity, stability, and cost considerations. Understanding these factors can provide insight into why most semi trucks opt for dual wheels.
Why Most Semi Trucks Have Dual Wheels
Dual wheels, often referred to as dualies, are a common feature on the rear axles of semi trucks for several reasons:
Weight Distribution and Traction
Weight Distribution: Dual wheels provide a larger surface area, helping to distribute the weight of the truck and its cargo more evenly across the road. This reduces the risk of damaging the road surface and minimizes the chance of tire blowouts. By spreading the load, the risk of uneven wear and premature tire failure is significantly reduced.
Increased Traction: Having two tires on each side increases the contact area with the road, improving traction, especially in adverse weather conditions or when driving on uneven surfaces. This is crucial for maintaining control and safety, particularly in challenging road conditions.
Load Capacity and Structural Integrity
Load Capacity: Dual wheels can carry more weight than a single large wheel. This is essential for semi trucks that frequently haul heavy loads. The dual configuration supports the structural integrity of the truck under heavy loads, ensuring safe and reliable operation.
Stability: Dual wheels enhance the stability of the vehicle, particularly when cornering or navigating uneven terrain. This is an especially important consideration given the size and weight of semi trucks, where stability is crucial for safety.
Cost and Maintenance
Initial Cost and Maintenance: While dual wheels may require more maintenance, such as checking tire pressure on multiple tires, they can be more cost-effective in terms of replacement and longevity compared to larger single tires, which can be more expensive and may have a higher failure rate.
Heat and Drag: A contemporary ten-wheel tractor has twenty flexing sidewalls, which can generate heat and cause drag and tire wear. Converting to duals reduces the sidewalls from twenty to twelve, reducing heat, drag, and wear. The increased number of wheels also means fewer failures and less maintenance.
The Debate: Broad Singles vs. Doubles
There is an ongoing evolution in truck tire technology, with both duals and broad singles being considered. This choice comes with its own set of pros and cons:
Pro: Reduced Heat and Drag with Duals
Dual tires are more expensive than single large tires, but they can reduce heat and drag due to their reduced sidewalls. The truck now has six wheels instead of ten, reducing the number of flexing sidewalls and thus reducing heat generation. Retreading these tires costs more, but not as much as with single large tires. Insurance companies particularly like dual tires because they reduce the risk of tire fires, which can be more severe with single large tires.
Con: More Significant Initial Investment and Modification
If a new truck is ordered with dual wide tires, its drive axles are about six to eight inches longer. This increase in length is necessary to ensure stability, as dual capacity tires are not twice as wide as two singles but must accommodate the space required between the singles. While this configuration provides superior stability, it also means that the truck can never be switched to conventional duals without changing the axles, which is a hugely expensive proposition. Some fleets see this as a non-starter, as it may discourage traditional methods of disposing of retired trucks.
Some fleets order new trucks with the wide tires but on standard-length axles, which makes the truck more saleable to traditional trucking companies. However, the company that bought the truck new forfeits the extra roll stability of the longer axles. Drivers may notice and discuss this, whether it is a real concern or not, as Mike Heaton suggests.
Conclusion
The choice between dual wheels and single large wheels on semi trucks is a complex issue influenced by weight distribution, traction, load capacity, stability, and cost considerations. While dual wheels offer distinct advantages in terms of load capacity, stability, and reduced heat generation, they come with their own set of challenges, particularly in terms of initial investment and potential modification costs.
As the trucking industry continues to evolve, the balance between these factors will need to be carefully considered to ensure that semi trucks remain safe, efficient, and cost-effective in the years to come.