Tread Safely: Maximum speeds, inflation play roles in tire performance

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When it comes to vehicle safety, a lot of attention is being focused on the one truck component that actually touches the road. The Rubber Manufacturers Association proclaims the first week of June as Tire Safety Week. Days after this concludes, the Commercial Vehicle Safety Alliance begins a special focus on tires as part of the annual Roadcheck inspection blitz.

Other components will still be inspected during Roadcheck, of course. But this year there will be a little more time spent measuring tread depths, checking pressures, looking for items lodged between the duals, and searching for cuts or bulges in tire sidewalls.

It makes sense. Tire condition plays a role in everything from stopping distance to stability. But it’s also important to ensure the right tires are selected in the first place.

Buyers should consider tire sizes, load-carrying capacities, maximum speeds, and type of service, says James Kiriazes, director – market performance engineering at Bridgestone. When all those factors are considered, the recommended choices quickly come to light. “You start to whittle down the selection very quickly,” he says.

The maximum speeds might take some long-time truck drivers by surprise. Such speeds are posted on some tire sidewalls, but not all of them, says Bridgestone project engineer Roger Best. “There is no ruling or law.” The details might only found in product data books.

This is a particularly important consideration for cross-border fleets that might have tires rated at 120 kilometers per hour, but routes where posted speed limits are closer to 130 kilometers per hour.

The ultimate damage from excess speeds might not emerge right away, but there is a price to pay for exceeding design limits of any sort. Tires, for example, don’t respond well to factors like excess heat. The problems might manifest themselves in the form of irregular wear, which can limit retreading opportunities. Chunks might tear out of a tread. And, of course, there can be outright failures.

Keeping a close eye on inflation pressures will help eliminate many potential problems, but Kiriazes recognizes there are limits to how often gauges are being applied to valve stems. “It becomes more and more challenging on the road,” he says, referring to the way fleets use options like team drivers to keep vehicles on the move. “When you’re driving in a team, and a truck is slowing down [just] to stop at a rest room and get fuel, then it challenges everybody.”

The most accurate inflation pressures are recorded when tires are cold. That means letting a truck sit three to four hours before noting the readings, Best says. “Overnight is the best option.” Weekly checks will identify many emerging problems before they take hold.

Even slight variations in tire pressure can sacrifice everything from fuel economy to tire life. Tires underinflated by as little as 10% can reduce fuel economy by 1.5%, while a 20% drop in pressure can reduce tire life by 30%, according to the Technology and Maintenance Council of the American Trucking Associations. Bendix, which offers Tire Pressure Monitoring Systems, also notes that 90% of blowouts are caused by underinflated tires, which increase stress and temperatures alike.

When pressures drop 20%, a tire is actually considered flat and needs to be removed, Best says. At that point it is a matter of tracking down a root cause, whether the air was lost because of a damaged tire rim or valve core, or because the wrong tire was used.

Tires don’t always fail because of a single problem, either. Problems might be the results of combined factors such as exceeding maximum recommended weights and running close to the edge of recommended inflation pressures. Every individual challenge adds to the next. “Tires don’t repair themselves,” explains Kiriazes, referring to the damage linked to everything from excess speeds to extra deflection.

“If you run over a curb, or you do something to a tire, that stays with it. It is not like a bruise you get on your arm,” Best says. “Tires always remember.”

Tire safety tips

  1. Set and maintain proper cold inflation pressures. Cold inflation pressure is the inflation pressure of tires before they are driven.
  2. Abide by the tire’s maximum recommended speed, which may be lower than posted speed limits.
  3. Select the right tire for the job, considering the proper tire size, load-carrying capacity, speed capability and service type.
  1. Inspect tires frequently for damage such as cuts, cracks, bulges and penetrations.

–       Source: Bridgestone

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John G. Smith is Newcom Media's vice-president - editorial, and the editorial director of its trucking publications -- including Today's Trucking,, and Transport Routier. The award-winning journalist has covered the trucking industry since 1995.

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