Take a closer look at some of the 18-wheelers rolling down the nation's roads lately and you might notice something missing: eight wheels.

Some truckers are converting to wider tires that let them replace dual tires with single tires, turning their rigs into 10-wheelers to reap fuel and weight savings.

The new tires are wide enough to make a hot-rodder happy. And they're drawing stares on and off the highway.

People ask Jim Smith questions about the expensive, Hulk-sized tires all the time at his showroom at Exit 11 Truck Tire Service Inc. near Interstates 80 and 77 in Richfield, Ohio.

"I tell them it's the future," Smith says. "It seems to be where truck tires are heading."

Each tire alone weighs close to 200 pounds. That future isn't cheap. Mounted on an aluminum rim, the tires can run $1,250 or more, Smith said. That's twice a traditional tire's cost.

It's worth the expense, said Luc Minguet, chief operating officer of Michelin America's truck tire unit. The tires can save 4 percent to 10 percent on fuel. That's a big consideration for transportation companies weathering diesel prices that soared from a U.S. average of just under $2 a gallon a year ago to a post-Hurricane Katrina peak of $3.16 a gallon in October.

"That 10 percent fuel savings -- that's huge," Smith said.

While Michelin may push fuel savings as a sales point, that can be elusive, said Robert Braswell, technical director of Maintenance Council of the American Trucking Associations. Fuel consumption can vary as much as 35 percent depending on whether a leadfoot or lightfoot is behind the wheel, he said.

Minguet also notes the tires are lighter. A 10-wheeler saves 730 pounds and lets trucking companies haul more cargo, he says.

The weight savings, however, is a big factor, particularly for tanker-truck companies, Braswell said.

Carl Smith, owner of 3J Fuels Inc. in Champlain, N.Y., has been using Michelin's tires on his tanker trucks for about a year. His trucks don't haul fuel long distances, so he said he hasn't seen much in the way of fuel savings. But the wider tires are helping him stay within legal weight limits and "seem to ride better," he said.

The big tires are still only a small part of the more than 17 million truck tires shipped in the U.S. this year. Competitor Goodyear Tire & Rubber Co. decided not to introduce its own line after the company found a variety of problems in testing its version, said spokesman Dave Wilkins.

A key issue was the reliability of retreaded tires, said Wilkins. That's a huge consideration for trucking companies accustomed to sending worn tires off to be wrapped in new tread two or three times during their life spans.

Michelin spokeswoman Lynn Mann said that's not a worry for Michelin. The company says some of its tires can last more than 800,000 miles with its retreading process.

Contract Freighters Inc., one of the nation's 50-largest trucking outfits, has become a big believer in the tires. By next year, its fleet of 2,300 tractors will be using Michelin's wide tires and the company has ordered them for 1,000 new trailers it will buy next year, Michelin said.

The tires have downsides. For instance, a flat puts the truck on the side of the road, while trucks with dual wheels blow by on the Interstate. Before tire dealers like Exit 11's Smith stocked the tires, that could mean more downtime while a driver sought repairs or a replacement, Braswell said.

That will be less of a problem as trucking companies embrace technology that monitors tire pressure, Braswell said.