MONTREAL, Que. - Michelin has developed a new wide-base tire - by now many of you have probably heard about the X-One - that does a lot for fuel efficiency and safety.But Michelin has a problem where ...
MONTREAL, Que. – Michelin has developed a new wide-base tire – by now many of you have probably heard about the X-One – that does a lot for fuel efficiency and safety.
But Michelin has a problem where regulations limit the weight allowed on a single tire. With restrictive tire-load limits, it doesn’t make sense to switch to wide-base tires in place of duals, because you can’t run weights anywhere close to the allowed axle limits.
Ralph Beaveridge, marketing manager for Michelin in Canada, voiced his concerns with the regulations at a meeting of provinces and industry in Montreal on Nov. 6.
Most Canadian jurisdictions limit single tire loads to 3,000kg because studies have shown that wide-base tires put more strains on pavement than comparable dual tires.
One such study was conducted in the early 1990s at the U.S. Department of Transportation’s Turner Fairbank test facility in McLean Virginia. It concluded that wide-base tires produce four times as much fatigue damage and twice as much rutting damage as dual tires.
Fatigue damage to an asphaltic concrete pavement, the most common pavement in Canada, is the cracking that occurs because of strains caused at the bottom of the asphalt layer when a heavy tire runs over the top of the asphalt. Rutting is caused by the vertical stresses that go right down through the pavement to the subgrade.
Wide-base tires of the past were particularly damaging because they had a smaller footprint, the contact patch between the tire and the pavement, than comparably loaded dual tires. Also, since wide-base tires typically required high pressures (115 to 130 psi), the problem was aggravated because the tires became more rounded as pressure increased and this further concentrated the strains on the pavement.
But Michelin has solved these problems with its new tire. The X-One series uses an 850-metre long metal cable wrapped round and round the tire with the casing to make a wider, flatter tire. The 445 mm (17.5 inch) X-One has a contact patch that is typically 375 mm (almost 15 inches) wide or about 15 to 36 per cent wider than the wide-base tires on the market prior to this. Because of the way the tire is designed, and because it operates at lower air pressure (100 psi), it also runs flatter. As a result, the contact stresses between the tire and the pavement are more uniform across the face of the tire. This helps reduce pavement damage.
That all-important cable might as well be made of red tape, however, as the provincial administrators have thus far refused to budge on their now, at least partially, obsolete restrictions on oversized-rubber.
At a limit of 3,000kg per tire, a tandem axle can only carry 12,000kg. That’s not much compared to the typical load limit of 17,000kg in Western Canada or the 18,000kg from Ontario east. Even on runs into the U.S., where tandems are held to 15,422kg (34,000lb), the new X-Ones don’t make a lot of sense on the Canadian leg of the trip.
Stateside, the new tires can run at full axle loads, as there are no tire-load limits. While many states have a limit on the load per inch of tire width, these new Michelin tires easily exceed the most limiting cases. So presently, the only carriers in Canada able to cash in on the X-One are those hauling low-density freight.
As for those benefits, they don’t come in savings in tire costs as one new wide-base tire costs about the same as two conventional dual tires. But one tire does weigh less than two and, at a saving of about 56kg per tire, a typical 18-wheeler saves 450kg. This weight savings, along with better aerodynamics in comparison to other wide-base tires and lower rolling resistance, can mean a fuel savings up of to four per cent.
That, at least, was the savings reported with the new Michelins at the Society of Automotive Engineers’ International Truck and Bus Conference in Portland, Ore. last year.
There are other benefits. Tractors and trailers with wide-base tires are more stable because the initial tendency to roll is lower than it is with dual tires. Probably of greater importance, wide-base tires allow trailer manufacturers to move support beams further apart (by about a foot). This, in association with the trailer’s suspension, makes for a more stable vehicle.
Finally, there is the possibility – and no one seems to have hard numbers on this – that wide-base tires offer slightly better braking performance. In hard braking applications, there is more drum exposed to the air which can keep brakes cooler and working at a higher level.
Now the problem for Michelin is getting the provinces to rescind the 3,000-kg limit on tire loads.
That won’t be easy according to the provincial representatives at the Montreal meeting. “How,” they ask, “will inspectors be able to tell one wide-base tire from another?”
“What’s needed,” they suggest, “is some means of certifying those wide-base tires, like Michelin’s, that are pavement friendly and then having some identifying mark so inspectors can tell which tires are which.”
Perhaps, they could simply look for the big “X-One” splashed across the sidewall in question…
In any event, most people at the meeting weren’t optimistic any regulatory change could happen in the near future, ensuring Michelin’s very useful product sits needlessly out of the reach of the majority of Canadian fleets.