While the tire industry doesn't talk much about the plus-sized tire phenomenon, it should.
Guy Edington, managing director of Kumho Tire Co.'s North American Technical Center in Akron, believes ignoring that niche means ignoring potential profits for tire makers and dealers alike.
``A niche market for near-broke adolescents in the '60s has become the principal and almost sole profit center for every major tire manufacturer,'' Mr. Edington said at the 20th annual Clemson Tire Industry Conference March 10-12 at Hilton Head. But although the plus-sized market offers great opportunities, he added, the differences between plus-sized and regular-sized tires must be taken into account.
``Drive around Los Angeles freeways for one day, and you'll see it,'' Mr. Edington said about the plus-sized market. ``Japanese cars will have 17- or 18-inch tires; SUVs will have 20-, 21-, 22-inch tires. In Akron and other places with potholes, you won't see much of this.''
According to Mr. Edington, drivers seek out plus-sized tires to personalize their vehicles, improve performance and enhance performance-oriented appearance. The 1964 Pontiac GTO gave birth to that market, he said, but the vehicular developments of the 1970s created the conditions that caused it to grow exponentially.
``In the '70s we had cars of demonstrably poor quality-some of the least desirable vehicles ever built,'' he said. ``This drove people to foreign cars and trucks, both of which are now the biggest plus-sized markets.''
The 1980s provided more growth in the market with more disposable income and ``the great leap forward'' taken by tire performance, Mr. Edington said.
``The '90s brought it to fruition with a Golden Age of Affordable Performance and with personal wealth at an all-time high,'' he added. During the '90s, diameters went from 17 to 20 inches, profiles dropped to 30 series, profits from non-performance tires dwindled and Internet sales allowed the proliferation of low-volume, plus-sized tires, he noted.
The first decade of the 21st century portends no end in sight to plus-sized market growth, particularly since new federal tire safety laws had a minimal effect on those tires, Mr. Edington said. The upper size of plus-sized sport-utility vehicle (SUV) tires has risen in a very short time to 28 inches from 20, he noted.
A potential stumbling block with plus-sized tires, however, is load capacity. If you ``plus one'' a vehicle-go up to the next available tire size-the classic load-carrying equations work well, according to Mr. Edington. But after ``plus two''-two sizes or more up the scale-the loss of rim diameter causes a significant loss of load carrying ability that the classic equations can't measure.
``You need to go to the load tables,'' he said. ``The problem is that tire engineers have the load tables, but tire dealers don't. We need to get them this information.''
Bead seating also becomes an item to watch in plus-sized tires, Mr. Edington said. Plus-sized tires have less sidewall area and more bead circumference than smaller tires, so seating pressure tends to go up. Also, with plus-sized tires there is increased air permeability at the bead.
``Aluminum wheels are notorious for wicking air out of tires,'' he said. ``Because of the low aspect of plus-sized tires, you can't see when the tire is underinflated or even flat. They don't look flat when they lose air.''
On the other hand, plus-sized tires generally have improved high-speed durability and much better handling, without increasing the tendency of some SUVs to roll over, according to Mr. Edington. But hydroplaning and bump protection can degrade, he added.
Mr. Edington predicted the ``Bigger is Better'' movement in tires will continue. He said the common size for plus-sized passenger wheels will reach 20 or 22 inches. In SUVs and light trucks, he added, some tires may go to 30 inches, though that's unlikely. ``Twenty-six inches will probably be the biggest commercially viable size,'' he said.
The Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act poses no major obstacles to the plus-sized tire market, Mr. Edington said, although the current bead unseating and bruise tests don't apply to ultra-low-profile tires.
A law such as the one in California, however, with the potential to mandate the same rolling resistance for replacement tires as for original equipment tires, could affect or even kill the plus-sized market, he added.
But despite this, Mr. Edington was optimistic. ``The desire to personalize vehicles will continue,'' he said. ``It's been an American birthright for the past 40 years.''