FYI from MCI™

Super-wide tires raise super-weighty issues

When Michelin first started offering its X One 17-inch-wide tires — each of which is intended to replace a pair of conventional dual tires — to its coach customers, it promoted the tires' fuel efficiency as a primary benefit. MCI decided not to offer them, but not because MCI is slow to embrace new ideas, as one trade publication indicated. Rather, it's because MCI is quick to protect the interests of its customers.

Paul Murphy, director of regulatory compliance for MCI, points out that the tires put operators at risk of getting sidelined at the weigh station, or during safety inspections because of the U.S. Federal Bridge Gross Weight Formula distribution limits. He refers to the rule at Title 23CFR §658.17, administered by the United States Federal Highway Administration, Department of Transportation.

"The tires were first offered to truck customers, and they work for that application," says Murphy. "Although coaches have tandem-style axles in the back,  they don't carry weight in the same fashion as trucks, which carry the weight equally. The bridge formula mandates that there can be no more than 500 pounds of weight per inch of width on any one tire. Using that formula, the two just-over-17-inch-wide tires can legally carry only about 17,700 pounds, compared to 24,800 for an axle equipped with duals.

Murphy has approached Michelin and another coach manufacturer that is offering the tires with this concern because he believes that the passenger transportation industry, which has fought long and hard for certain weight exemptions, risks those gains and its future bargaining power by operating coaches that break the rules.

Other problems

Peter Zammuto, MCI marketing program analyst, additionally points out that the wider tires may present other challenges to coach operators. The wider tires are too big for the spare tire compartment, and the tire-and-rim combination is very heavy and hard to lift. Those operators who might feel compelled to carry two spares would have to use  the baggage compartment, sacrificing space that might otherwise be allocated to passenger luggage.

For those who don't carry spares, there could be even more trouble down the road. In the case of a flat tire, it may be difficult to find a service facility that has a super-wide tire in stock, especially in remote areas. And, says Murphy, because federal rules require that tires match in type from side to side, if an emergency service provider without a matching tire were to attempt to get the coach back on the road by replacing one big wheel with two normal wheels, it would also have to do the same thing on the other side of the axle to avoid regulatory problems. And that could add up to extra time and money.

Will MCI ever offer the super-wides as an option? While one should "never say never", MCI can't, in good conscience, offer them under current configurations and regulations.

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