Plus-sizing tires and wheels may be the hottest trend around the industry, but this can be a problem once the snow starts flying, sources told Tire Business.
Consumers Union, which publishes Consumer Reports (CR) magazine, last year put plus-sized tires to the test for a report in its January 2004 issue. ``It's something that we've seen our readers are interested in,'' said Eugene Petersen, program leader for tire testing at CR.
The group found plus-one tire and wheel packages offered gains in overall performance, especially in cornering and emergency handling. But higher sizes carried other issues in addition to their higher price tags.
``As you increase your rim size those gains, even though they were improvements, they were not large improvements,'' Mr. Petersen said. ``On the negative side, though, as you increase beyond the plus-one scenario, we saw large decreases in hydroplaning performance, a much stiffer ride and much less snow traction.''
In fact, with a plus-one package, the three vehicles tested-a 2002 Honda Accord, a 2001 BMW 530i and a 2002 Chevy Tahoe-averaged a 5-percent loss of snow traction. With a plus-two setup, the vehicles lost about 20 percent snow traction, and plus-three packages suffered a loss of more than 30 percent snow traction.
The tires tested were all-season treads, with summer-rated tires on the BMW. But experts said plus-sized winter tires probably wouldn't make up all of the snow traction lost.
John Clancy, ultra-high performance key account manager for Pirelli Tire North America Inc., estimated a motorist with plus-sized all-season tires who switches to plus-sized winter tires probably would see 25-30 percent better snow traction. But if the same motorist put on winter tires in the original equipment size, he or she would see 65-70 percent better traction.
For this reason, Pirelli recommends going back to the base original equipment wheel size for winter tires.
``That really saves the consumer a lot of money,'' Mr. Clancy said, referring to cheaper wheels and tires in the lower sizes. ``It also takes their nice wheels and tires off during the salting and sanding season so they don't get all pitted and scratched up.''
Potholes posed just as much danger to the larger, more expensive rims, CR found. Mr. Petersen said the plus-two package on the Honda suffered damage, as did the $2,150 plus-three set on the BMW.
Bill VandeWater, consumer products manager in sales engineering for Bridgestone/Firestone (BFS), said the main snow traction problem is that as tires go up in size they also widen out, which causes flotation over the snow instead of cutting through it.
``As long as you're floating on top of snow, you're not getting the most traction,'' he explained. ``It's very slippery up there on top. Instead, if you can dig down in, you can get into the moister snow.''
BFS also recommends minus-sizing for winter tires, or coming down to the smaller diameter OE sizes. In addition to less traction from the tires, the vehicles that usually are plus-sized-high- power performance vehicles-aren't well suited for the snow in their own right, he said.
Getting that message across to consumers usually is the job for tire dealers and makers.
``It's not really well known out there,'' Mr. VandeWater said. ``People will go to the plus-sizing...for their summer tires, and then when it comes time to buy winter tires, they just won't give it a second thought. They'll get the winter tires in the same size.''
He suggested dealers get a feel for customers' needs: What area of the country do they live in? What are their driving habits? What are typical conditions for the roads and time of day they usually travel?
Then dealers could explain how narrower tires work better in snow, and while they would cut some overall performance, it's just for the winter.
This method leaves room for two opportunities for dealers: selling a set of steel or less expensive wheels and stocking the summer rims to guarantee a return trip in the spring. Mr. VandeWater said a dealer can-either for a fee or not-store the expensive rims and promise to refit them in the spring when there's another chance for an inspection and possibly further sales. Even if the dealer doesn't have storage room, an offer to switch out the winter wheels will have the same outcome.
``That person returns to your location twice a year,'' he said.
Mr. Petersen at CR said snow traction should be just one more issue tire dealers carefully consider when plus-sizing tires, in addition to calculating the load capacity and extra weight of the wheels.
Pirelli's Mr. Clancy said the trend toward bigger OE sizes also lights a fire under tire makers. For example, while Pirelli makes the 15- and 16-inch standards, it also makes winter tires in 17- through 19-inch rim diameters for passenger vehicles to meet optional fitments from auto makers. While he said tire makers are constantly designing along with this trend, they continue to make the bulk of their volume in the lower sizes with less product available at the ``exotic'' high end.
``What ends up happening is supply and demand ends up pushing (customers) into what they really should buy,'' he said.
In the end, he said, customers usually will be willing to switch down if they're given knowledgeable information from tire dealers.
``They may not completely like going from the 18-inch wheels to a 16-inch or 17-inch wheel because they lose a little bit of the looks, but I think usually they're smart enough to understand why,'' he said.
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Consumer Reports conducted plus-sizing tests on three vehicles-all shod with all-season tires. Their results:
* Plus-one-average loss of 5 percent snow traction.
* Plus-two-average loss of 20 percent snow traction.
* Plus-three-average loss of 30 percent snow traction.