Going Single in a Dual World

By now you have likely heard about the new single wide-base tires – super wides,

as we call them – being offered for line haul applications by several of the major truck tire manufacturers. Michelin, Goodyear, Bridgestone/Firestone and Continental all have their versions, and all are in various states of development or marketing.

Before jumping to any conclusions or recalling experiences with earlier generations of wide-base tires, there are some important things you should know.

The earlier wide-base tires were originally designed for high load and extra flotation applications on vehicles that operated in mixed-service – or combination on/off road ®“ environments. Heavily loaded steer axles of ready-mix concrete trucks, waste haulers, brick/block delivery trucks and mobile cranes are examples.

These vehicles generally operated at limited speeds in local delivery duties. Three sizes have been popular, 15R22.5, 16.5R22.5, and 18R22.5.

These tires date back to at least the early-1960s and were originally bias ply designs that have since been converted to radials. They were renamed to more current metric size nomenclature (385/65R22.5, 425/65R22.5, and 445/65R22.5, respectively) during the mid-1980s/early-1990s time period. They are evolutions of, and share many design features and material types with, their more conventional 75 to 90 aspect ratio counterparts typically used in dual tire pairings on drive and trailer axles.

Over the years, some innovative truckers have fitted these single tires in place of duals on drive and trail axles with varying degrees of success and difficulty. Certain bulk haulers and local fleets have been the most vocal advocates. Weight savings (lighter tare weight), and reports of improved fuel efficiency vs. duals have been the most commonly cited attributes.

On the other hand, driver acceptance, sustained high-speed durability, replacement tire availability for over-the-road in-route failures, lack of limp-in capability, and axle width/wheel offset dimensions have been common issues.

In short, these earlier generation wide singles showed significant promise in line haul service, but were limited by their heritage of vocational designs, a spotty supporting infrastructure, and axle-end hardware originally tailored for dual tire fitments.

Evolution by Design

Fast forward to the current crop of line haul tire offerings.

Tire manufacturers have continued to achieve evolutionary, yet significant, advances in truck tire tread life, casing durability, fuel efficiency, and retreading technology during the past decade.

But in the last several years, bus and truck manufacturers, primarily in Europe, have begun asking for new single tire technology that could take vehicle space utilization, ride and handling, and operating efficiency to new levels. More space means more cargo, more comfort and more income.

Some vehicle designs have been specifically modified to allow single tire fitment – wheelhouse enclosures, cargo storage areas, axle and suspension components, While that may preclude retrofitting to duals, cost advantage was the driving factor.

There is also an increasing emphasis on improving ride comfort and dynamic handling characteristics of many new global truck and bus platforms. Again, super wides are under consideration there.

Tiremakers have been working on these challenges, developing a somewhat fresh approach with super wides. But this work has not been without its own set of challenges, mostly in existing production (how do you make them?) and tire technology (how do you move past current 75- and 80-series line haul type tires?).

For example, the wider tread of the new generation single tires needs to be shaped and restrained more positively in the crown area than allowed by current belt packages. One answer applied by a manufacturer is the winding of a single strand of steel cord circumferentially and across the tire face.

Also consider that with half as many sidewalls and beads on a super wide vs. conventional duals, more of the lateral forces controlling cornering and handling will be transferred to the wheel. However, this reduced number of flexing sidewalls can also be expected to result in lower tire rolling resistance and improved fuel economy in over-the-road service.

Another consideration is that positioning the outer tire sidewall of the super wide single tire as far outboard as the current dual tire requires the use of significant wheel offset, a source of concern to several of the major axle, hub and bearing suppliers. Reducing the overall track width may raise driver issues of perceived stability problems, and complaints of not being able to see the tires in mirrors as readily when checking clearance for cornering, backing or periodic visual inspections. Some industry sources suggest the best solution may be wider axles than are currently used with the dual tire sets.

Advantages Aplenty

Despite some of the challenging issues, several industry trends and concerns could be positively impacted by a growing acceptance of super wide single tires in place of duals. First, it is now documented by studies that the majority of roadside tire debris results from underinflation. This knowledge, considered together with an emphasis on reducing maintenance requirements, costs, and tare weight, favors the use of tire systems that eliminate eight of the 18 wheel positions on the rigs of today.

Even if inflation maintenance systems were fitted to these vehicles, the complexity and costs would be reduced with fewer tire valves requiring hookups.

Labor saving may be possible if larger inflation valves, such as those used on earthmover-type tires, are adopted with the new single tires. This would reduce the time required for inflation when mounting, and may even improve tire/wheel assembly uniformity due to the more rapid bead seating.

One intriguing question that remains to be addressed is the fate of steer axle tires of current 75- to 90-series design once their initial tread life has been realized.

The Road Ahead

There appear to be some very promising advances possible with the new super wide single-tire concept and other recently announced developments. There is no doubt this growing technology could dramatically change the appearance and performance of the 18 wheelers we know today.

It would seem to be an excellent opportunity for vehicle and tire manufacturers and component suppliers to work together to develop complementary parts and engineering designs that will allow the full benefits to be derived from this technology.