TORONTO, Ont. – When a tire design promises lighter weights, better fuel economy, quicker installations and smoother rides, you would normally expect it to be a hot seller. But despite these attributes, Canada’s use of wide-base tires continues to be limited by weight-related restrictions.

The tires — sometimes known as “super singles” — were initially designed to meet weight limits imposed on U.S. interstates, which set maximum axle loads at 7,710 kg.

By allowing 8,000-kg axle loads on semi-trailers, Quebec set up an environment that makes the tires viable for southbound fleets. But the problems emerge if you want to travel east or west. Other provinces limit individual tires to loads of no more than 3,000 kg, so the resulting 6,000-kg axle limits mean wide-base tires aren’t a viable option for most operations.

Ontario, meanwhile, recently dealt a blow to hopes that it would increase allowable weights by releasing a study that insists the tire designs are up to 12 times more damaging to roads than dual wheel assemblies.

Those who make the tires, however, are countering with arguments of their own. New shoulders and sidewalls help keep the latest generation of tires from deforming as they travel down the road, ensuring a constant amount of contact with the asphalt. And a recently released Society of Automotive Engineers (SAE) study suggests the designs may even better protect road surfaces when you consider the way they hop over bumps and ruts in a real-world environment.

Current Canadian sales of the tires remain a tightly guarded secret. Since Michelin (makers of the X-One) and Bridgestone-Firestone (the Greatec) have been the only sources of the designs, neither has been anxious to reveal market shares. Goodyear, meanwhile, will only begin producing its G392-SSD and G394 SST offerings this spring.

But regardless of the restrictions, there are still benefits for selected Canadian buyers who are considering the tires.

“Theoretically, new wide-base singles can replace any dual drive and trailer position for linehaul, regional and local haul applications,” says Brian Rennie, of Bridgestone-Firestone Canada’s Sales Engineering Group. “Any weight-sensitive operation, like tankers, can take clear advantage … I can foresee city bus operators considering this technology, which will allow bus manufacturers to widen axles and, consequently, the floor area, to better accommodate passengers.”

After all, other than the weight restrictions, the tires offer many benefits, not the least of which is the promise of a four per cent increase in fuel efficiency.

“Depending on speed, about a third of the fuel is consumed to overcome tire rolling resistance,” Rennie says. “There is a friction between the tire and the road, energy lost from the deformation of the tire under load, and internal stresses within the tire itself. Most of the rolling resistance of a tire is a result of tread design and compounding. The tread typically contributes 60 per cent to 70 per cent of tire rolling resistance and the casing 30 per cent to 40 per cent.”

The improvements are possible when you consider that a dual assembly’s four sidewalls are replaced by the two sidewalls of a wide-base tire, he says, adding this reduces the internal stresses that generate rolling resistance.

And while the tires are restricted in the weights they can carry, they are able to shed pounds from existing equipment. The use of Michelin X-Ones, for example, can save about 200 lb. per axle when compared to the weight of dual tires. And the weight savings are even greater if you’re shifting from steel rims to aluminum rims in the process.

Drivers, meanwhile, experience the difference in the seat of their pants.

“A good part of that comes from the larger volume of air inside the tire, so it acts like a shock absorber,” says Michelin’s Ralph Beaveridge. “Take a look at racing tires and how they offer improved handling. They’ve shortened the sidewall and widened the tread width.”

The tires also offer the opportunity to lower maintenance costs, since a single tire can be replaced more quickly than the inside tire on a dual assembly, he adds.

“And when you have dual tires, the inside (tire) is often a lost soul. Rarely is its pressure checked,” Beaveridge says, referring to a study by Robert Transport, a Quebec-based fleet that suggests about 40 per cent of inside tires are mismatched because of low inflation pressures.

The reason is obvious, he adds. “The inside duals are difficult to reach. You’re stretching your hands through the hand holes to stick your gauge on a valve stem that may be dirty.”

But one of the remaining challenges involves a wide single’s retreadability, says Goodyear technical marketing manager Al Cohn. Most linehaul fleets expect at least two additional treads on a tire’s casing. With wide singles, the pressures need to be perfectly maintained to ensure they can be retreaded once.

“It’s the heat,” Cohn explains. “Natural rubber is an insulator, and heat is the worst enemy of a tire.”

It’s one of the reasons that Goodyear expects the use of its coming tire to be limited to niche markets, such as regional fleets that operate within a 300-mile radius.

And there’s the obvious challenge associated with breakdowns if a tire goes flat. “You don’t have any limp-home capabilities,” he says, comparing the single to the loss of one tire in a dual assembly. “If the truck goes down, it’s stuck.”

These aren’t the only challenges facing the tires. Several sources familiar with the designs say a roadblock has emerged in the Toronto area, where one inspection station has begun to issue tickets to vehicles that were once allowed to pass through to the U.S. That means Quebec fleets that once cut through the province now have to run directly south, or take their chances at Ontario scales with an argument that they’re well within allowable axle load limits, even if individual tires are overloaded.

For now, supporters of the tire designs continue to push for weight-related rules that would allow the wider use of the tires. Michelin and the Rubber Association of Canada have been lobbying federal officials to adjust the per-tire limits. And that means a battle of the studies.

“I’m not convinced that (the MTO studies) accurately reflect what is happening in the field,” Rennie adds. The province’s conclusions, for example, assume that dual tires are matched in terms of inflation pressure and diameters — offering an even amount of pavement contact.

“But in use, these tires, more often than not, are unequally matched so that one of the tires is actually supporting a significant portion of its mate’s share of the load.”

The debate shouldn’t even be limited to pavement damage, Beaveridge adds, referring to the need to consider other “socio-economic” benefits such as improved fuel efficiency and lowering levels of Greenhouse Gas emissions. “And by widening the space between the tires, we can allow the tanks (of dangerous goods) to go lower between the tires … to increase their stability.”

“We’re not asking the government to sacrifice the roads for the benefit of the industry,” he says.

Supporters of the designs simply want regulators to consider all the advantages.