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Traction In A Winter Wonderland

TORONTO, Ont. - A new law mandating the use of snow tires in Quebec has caused a national shortage of winter tires for passenger vehicles. While it's not likely the Quebec legislation will have commer...




TORONTO, Ont. –A new law mandating the use of snow tires in Quebec has caused a national shortage of winter tires for passenger vehicles. While it’s not likely the Quebec legislation will have commercial vehicle operators rushing out to equip their trucks with winterspecific tires, Brian Rennie, sales engineering with Bridgestone Firestone Canada points out “The truck tire market is evolving very similarly to what the passenger car market has done.”

So does that mean it’s time to stock up on winter tires for your heavy trucks in anticipation of a shortage? That may be an overreaction, but it’s definitely a good time to give some thought to traction as the snow begins to fly.

Winter-specific or all-season?

Canadian winters are so unpredictable, that choosing a tire that will perform well in all conditions is a challenge.

“Winter is comprised of all weather variations, including: dry; wet; slush; ice; snow; and everything in between,” points out Rennie. “Any tire will have trade-offs and compromises.”

Full-fledged snow tires are still used in some applications and regions, for instance logging in the northern reaches of Quebec. However, winter and all-season tires are more common, notes Rennie.

“The majority of the industry is going to be running all-season, mixed tread patterns,” he says.

All-season tires can be adept at providing traction in winter conditions, provided they have a tread design that’s intended to run in the various elements that winter presents.

“We have looked at pure dedicated winter tires for commercial vehicles and we found that we’d have better success with something a little more broad-based,” says Yokohama’s Greg Cressman. Yokohama has found that winterspecific tires are more vulnerable to irregular wear, due to their deep treads and sometimes unstable blocks. Advances in tire technology have helped manufacturers design all-season tires that are equally capable of handling snow while maintaining regular wear.

Ideally, fleets and owner/operators should schedule their replacement cycles so they’re putting new rubber on in the fall, advises Tim Miller, commercial tire marketing communications manager with Goodyear.

“You can run your tires pretty low in the summer months,” he says. “The time to change them out is in September, October or early November at the latest.”

If you have the storage space and the resources, you can switch back to partially-worn tires in the summer for better fuel mileage. Otherwise, you can probably get the summer and at least another winter out of winter-oriented all-season tires, says Cressman.

Goodyear’s Miller suggests maintaining a tread depth of at least 8/32nds in the winter, even though some fleets run their treads right down to 2/32nds in the summertime.

While it’s economical to use tires of varying tread depths depending on the season, John Overing, heavy trucks segment manager, Michelin North America (Canada) points out tires of difference tread depths should not be used together. So, if you’re going to replace one tire in the summer, be sure to also replace its counterpart, he suggests.

“Even a 3/32nd difference in tire height results in one tire wanting to rotate more than the other,” says Overing. “A new tire paired with a tire that’s 50% worn, will cause irregular wear and decreased tire life.”

When choosing a tire for winter, an aggressive tread design is ideal, and Miller suggests selecting a tread pattern that has many “lugs” that will cut through snow and slush.

It’s often been said that open-shoulder designs are better at carving through snow, however Rennie says that’s not always the case.

“In reality, it has more to do with the geometry of the tread, the void ratio (the ratio of rubber to air in the tread pattern), the amount of biting edges and how many lateral grooves or sipes there are to bite through the snow and grip the ice,” he explains. “It’s a misperception that you need an open shoulder; for straight-ahead traction, an open shoulder is not necessarily better.”

Some of the best self-cleaning tires do combine an open-shoulder design with a high void ratio, however Rennie suggests talking to your tire dealer and remaining open-minded about closed-shoulder designs, which have their own advantages such as being easier to chain.

Winter maintenance

Tire pressures should be checked regularly any time of year, but it’s especially important in the winter, particularly if you run long-haul. Changes in ambient temperature can have a significant impact on tire pressures, according to Rennie.

He points out that driving from an area with an ambient temperature of 20 C to a place that’s -5 C can reduce tire pressures by more than 10%.

“You’ve gone from a situation where there’s adequate pressure to support the load for optimum tire wear, mileage and fuel economy to a situation where you may not have enough pressure to support the load, let alone the other side effects such as traction and tread wear and fuel economy,” he says. “Inflation pressure is critical.”

Underinflation of as little as 10% can shorten tread life by 9-16%, according to the Technology and Maintenance Council.

Tire pressures should be monitored constantly when travelling between areas of vastly different ambient temperatures, or even locally where weather changes quickly -say in Calgary which can experience 20 C temperature swings in the event of a Chinook. Unfortunately, it’s usually best to check tire temperatures outside, rather than in a heated shop, according to Rennie.

“The room temperature in the shop may be 20 C and then you go outside where the temperature is -5 C. You immediately become underinflated once the temperature equilibriates with the ambient temperature,” Rennie says.

Checking tire pressures outdoors does create a challenge, however. Miller points out moisture may escape from the valve stem causing the tire pressure gauge to freeze and provide an inaccurate reading. He suggests checking tire pressures indoors and then compensating for the ambient temperature by adjusting pressures accordingly. Goodyear suggests counting on a 1 psi drop in air pressure for every 10 F drop in ambient temperature. In extreme weather, the drop can be even greater.

Chain with caution

In some parts of Canada, such as the B. C. Interior, truckers are legally required to carry chains unless they’re using winter-specific tires. But chaining up can cause damage to tires if done improperly.

Two of the biggest mistakes drivers make are: installing chains upside down; and securing them either too tightly or too loosely.

“Chains certainly, if not installed properly, can do some damage,” Rennie says.

If they’re installed face-down, the sharp surfaces will eat into the tread and the cross-chain hook ends may cut the tire shoulders. If chains are installed too tight, a lack of movement will cause rubbing that can damage the steel cords within the casing. If they’re too loose, the whipping action against the road surface can also lead to tire damage.

It may seem like a pain, especially in blustery conditions, but Rennie suggests inspecting the chains and re-adjusting the tension about 5 km after first installing them. That’s because they have a tendency to settle during the first few kilometres of travel and may accumulate some slack. When done properly, Goodyear’s Miller says chains will not negatively impact tire life.

“But if you don’t pay attention and chains are not tight enough, or if you run on chains after they’re needed, your tires will face the consequences and suffer an early grave to the scrap pile,” he warns.

Proper training on how to chain up should be provided to drivers. A good guide on proper chaining techniques can be found on the DriveBC Web site at: www.th.gov.bc.ca/chains/index.htm.

Even in the harsh winter conditions experienced in Canada, a winte
r-specific tire may not be necessary. However, special attention should be given to the tread design and once a selection is made, proper care should be extended to the tire year-round to ensure maximum tread life and optimum performance.


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