Just when we thought tire sizes had reached their low-profile limit, just when we thought tire widths were shrinking engine-bay requirements, we started learning how little we actually know.

SUVs and light trucks became the “spotlight” ride of the 1990s and 21st Century. In 1996, Ford introduced the Expedition, and later, the Lincoln Navigator, and other vehicle makers followed suit. A simple badge change and a little sound-deadening material added $10,000 to $15,000 to the till.

And the stampede was on.

Owners of the Cadillac Escalade, for example, are more than willing to shell out $64,000 with options. Those who buy the stripped-down model (read: $57,000 and change) get size 265/65R18 rubber. Still, we all know that many owners of 2006 Escalades are opting for plus-two 20-inch packages. They will ask you to mount 285/50R20s, and they’re out the door while you count the day’s take.

Hold everything. The 2007 Cadillac Escalade comes with a 22-inch wheel option, offering even bigger tires and wheels. That’s about a two-foot-wide tire. If you didn’t already know, this is a factory first for an SUV. To this tire/wheel package, add a new 6.2-liter V-8, which replaces a 345-hp 6.0 liter V-8. For those of us on a budget, that’s 13 mpg in the city, 19 on the highway.

‘Big’ Caveats

Anyone in the business of changing out smaller OE fitments for mild-to-wild fitments should tell the customer that he or she is going to experience better handling and a much firmer ride.

However, big tires and wheels have their limitations, and it’s in a dealer’s best interests to know them.

Some of us old timers remember changing out OE size 7.50×14 tires for 8.25×15 tires for a wider, stronger look. I did that on my 1961 bubble-top Chevy with every factory goodie available. But, today, new rules and regs apply, and we can’t ignore them. The law dictates that we take a closer look at proper tire load-carrying capacity and tire/wheel fitments.

Trouble is, big wheels and tires add weight – as much as 40 pounds or more to the tire/wheel assembly when going from a 16-inch wheel to a 22-inch wheel. That’s unsprung weight, which was not accounted for by the vehicle maker. Expect it to cause traction loss, along with accelerated wear and tear on the tires and suspension parts. Braking distance can also be negatively affected. One study cites 60-to-0-mph stopping distance being increased by 20 feet.

Changing ride height can also wreak havoc on on-board computers. Because antilock brakes and stability control systems rely on speed data to keep the vehicle from losing control, their ability to function properly can be compromised when incorrect tire fitments enter the picture. In some cases, the vehicle systems that buyers pay extra for can be rendered ineffective.

When looking at tire load capacity, especially on SUVs, consider the fact that, once you add gasoline, people and possibly a boat or trailer, the vehicle can nearly double in gross weight. Be aware of such changes and become the dealer these customers need.

Clearance, Load Capacity

We mention these things because they can and do happen. Just ask Arnie Sperlin, owner of Globe Tire and Motorsports in Los Angeles. Sperlin admits that, when tiremakers introduced the 24-inch tire, he thought that was about as large as they could go. Then, there was the 26-inch, 28-inch and larger. “The bigger they come, the more we all make, but there must be a limit somewhere for wheel makers and tiremakers alike,” he says.

Sperlin, who counts on movie, sports and rock stars for 25% of his business, regularly fits Escalades with a plus-four package of 285/45R22s or, for those with the really big money, 305/30R26s mounted on Giovanna wheels. Ballpark cost for the latter package is $10,000 to $12,000.

To get the proper clearance and load-carrying capacity, Sperlin may have to lower the springs and add bigger brakes all the way around. Brembo is his favorite choice to halt the 403-hp, 5,800-pound block of Cadillac metal. Add another $3,000 to $4,000 for the Italian brakes. Those bright-red calipers clamp down tight on 14-inch rotors to bring the beast to a halt in good order. The southern California dealer will also cut metal if it’s required.

Safety Still First

Spence Sperduto, Redwood General Tire’s high performance tire and wheel expert, takes a very measured approach. He’ll let a customer walk rather than install a tire/wheel package that won’t carry the load. His boss, Alpio Barbara, agrees. “We just won’t do it,” says the Redwood City, Calif., dealer.

A pair of Ford Lightnings with 275/60R17s as OE was refitted by Sperduto with 295/45R20s, a plus-three treatment, along with 20×9 wheels. In Sperduto’s words, “These fitments meet all tire load-carrying capacity requirements and clearance issues. It’s the only way we work with customers who want a contemporary look. Period.”

Sperduto put 225/45R18s on a Mercedes Benz CLK 320 that came with 205/55R16 as OE. He’ll plus-two a Tahoe with 285/60R18s and take off the 265/70R16s that came as OE. His primary interest is making certain that the replacement tires will carry the load, that they will not experience any clearance issues and that the overall diameter is so close to OE that there will be no issues with the speedometer or other systems.

“Nothing goes out of here until I say it goes out of here,” he says. “We are not going to take the chance of surprising the customer with dashboard warning lights indicating their indirect TPMS system is malfunctioning. That is not the way to take care of a customer; it is not the way we do business.”

The bottom line for Sperduto is that nothing leaves his care if the TPMS system fails to work. “It just isn’t going to happen,” he says.

A 1999 Escalade given to Sperduto will probably leave the dealership with 285/50R20s, a plus-four treatment that replaces the 265/70R16s that came OE. Notably, Redwood General Tire will not remove metal to make something fit. Sperduto would rather talk to the vehicle manufacturer to see what fits.

A new Chrysler 300C that comes OE with T-rated 225/60R18 may leave Redwood Tire with extra-load, W-rated 265/35R22s. The downside of such a fitment, though, is that the tire upgrade will wear faster. The upside is better grip.

When Sperduto moves into the 22-inch range, he says it’s hard to find a tire that will work properly. Recently, he pulled 235/70R16 OE tires from a 2004 Mercury Mountaineer. The customer wanted a plus-four, 20-inch package. Although Sperduto did everything in his power to make it work, the customer didn’t like the ride. “We went back to the OE package,” he says.

The California expert talked about another improper fitment. The owner of a 2002 Suburban 3/4-ton came in with 245/75R16s with a load index of 120. He wanted to upgrade to a 22-inch package. Trouble is, there isn’t a 22-inch tire made to handle the load.

The fix: Put a torsion bar lift kit in front and a two-inch block in the rear and/or a shackle kit. There is a company that makes a 325/50R22 10-ply that has the sidewall height and strength to carry the load for this vehicle. This combination works, as long as the accompanying work is properly done.

Arm Them, Protect Yourself

So, how should dealers interpret day-to-day fitments in light of the warnings offered by a host of safety groups, tiremakers and vehicle makers?

The answer is to take a lesson from other dealers, such as Sperlin, Sperduto and Barbara. Develop loyal customers and prevent comebacks – as well as possible injuries and lawsuits – by sending your replacement tire customers on their way with your full backing.

It’s a reality today: Customers with no tire knowledge or load-carrying capacity training want you to plus size their OE light truck or SUV tires and then send them on their way.

Your job is to arm them with the kind of information and tire fitments that will keep them safe. Be sure to tell them that upgrading to larger tires and wheels will mean a ride-quality sacrifice, a very possible need for larger brakes and maybe a change in drive ratio, as well.

Get out your tire sizing and load index charts and study them closely. Don’t create a tire load-carrying capacity or TPMS issue that will come back to haunt you or your customer. You are a tire professional; there can be no better time to live up to your reputation.