Increasingly, people are trying to personalize or upgrade the look of their vehicles through the addition of new (and usually larger) wheels and tires.

The affect can be striking and that perhaps explains why such equipment is often called "jewellery" or "bling."

Driven by popular culture, installing new wheels and tires has become a huge business in North America. In 2003, Americans alone spent $3.2-billion (U.S.) to buy twice as many wheels and tires as they bought in 1993.

Unlike dangly earrings or a flashy chain, however, if the new wheels and tires aren't right for the vehicle, they can harm more than the owner's reputation for being cool.

Indeed, if the wheels and tires are the wrong type or installed incorrectly or even just too big, they can affect a vehicle's dynamics, usually in a bad way.

Bad as in a harsher ride, lower fuel economy and compromised steering Really bad as in a greater likelihood of rolling over or being in a crash, potential loss of warranty and insurance coverage and maybe even increased liability in a crash.

These are serious prices to pay for a new set of wheels or "rims" or "dubs." By any name, they are the round metal frame to which the rubber tires are mounted.

This was all made clear at a media program at the huge evaluation centre west of Detroit that General Motors uses to test, among other things, the design of tires and wheels for a specific vehicle.

It must be noted that GM has recently become proactive in its efforts to sell more upscale wheels and tires for its own products. And that tends to make its concern for people buying such items from other companies seem self-serving.

To a degree, it is, but that does not make any less compelling the point that new wheels and tires always change the way a vehicle behaves.

And that a bad installation or the wrong equipment can be a serious concern.

According to Carl Sheffer, vice-president of the Specialty Equipment Manufacturers Association, the situation is of real concern to many of the auto companies and many of the major tire firms.

Frank Taverna, GM's engineering group manager for vehicle dynamics and control systems, called going to new wheels and tires a "dilemma."

"By changing one element of a vehicle suspension system, many other elements can be impacted, affecting everything from ride and handling, to safety," he said.

To make it clear why this concern involved more than a marketing stratagem, GM put on a simple but compelling demonstration of what happens when you upsize a vehicle's wheels.

GM had arranged for the media to drive three pickup trucks that were identical except for their wheels and tires.

One was the standard set created by the company through its "holistic engineering" approach, one was a set of bigger wheels and tires that GM designed, sells and installs, and the third was a bigger set GM bought and had installed at an aftermarket shop.

The three trucks were driven over the same course to test their steering and handling and their responses to some potholes. The differences were obvious and sometimes remarkable.

The stock wheels and tires delivered by far the best ride and handling, balancing comfort and agility quite nicely.

The bigger wheels and tires GM designed delivered the harsher ride that using more metal and less rubber always does, but the truck still felt quite manageable.

The non-GM aftermarket wheels and tires, however, the result was considerably more dramatic and more disturbing. There was a clear sense the truck's dynamic integrity had been compromised. It was much harder to control and a lot less comfortable to handle all situations.

According to GM and Sheffer, this experience is not unusual with wheel and tire upgrades, though the executive director of GM's accessories program, Nancy Philippart, was quick to add there are "many good products out there."

Philippart also pointed out there are "very few truly integrated tire and wheel systems."

The importance of the need to integrate the wheels and tires into a vehicle's design was made clear by James Cutting, the director of GM tire-wheel systems.

"Wheels are the glue that bonds tires to the vehicle," he said.

"They are a key component of the suspension system, and precise fit with the vehicle is critical."

For the consumer, there is virtually no way to tell what an aftermarket set of wheels and tires will do to their vehicle's ride and handling, except to say it will almost certainly compromise them.

The only question seems to be how much will they compromise them, and what greater risks (safety, insurance, warranty) are involved.

For now, at any rate, the smart consumer looking to add some bling to their vehicles should at least consider what the original car company is offering.

Many of them are in the business of selling upscale wheels and tires already, and we can expect a lot more in the future.

Chrysler adds AWD versions

At least partly in response to concerns about the handling ability of a powerful rear-wheel-drive car in Canadian winters, Chrysler will add all-wheel-drive versions to its Dodge Magnum and Chrysler 300 models.

The AWD rollout starts early this fall with the 2005 AWD Dodge Magnum SXT and AWD Dodge Magnum RT, and will continue later in the fourth quarter with the AWD Chrysler 300, AWD Chrysler 300 Touring, AWD Chrysler 300 Limited and AWD Chrysler 300C.

On top of the actual price consumers will pay for the car, the Windsor, Ont., branch of Germany's DaimlerChrysler AG wants them to pay a "destination charge" of $1,100, which should provide the folks who live near the factory that makes the cars in Brampton, Ont., with some ironic amusement.

All prices of course include the added front differential, transfer case and all-wheel-drive front suspension, performance disc brakes, and a 72-litre fuel tank in every model.

The AWD Dodge Magnum SXT will list for $34,205, and this includes a five-speed automatic transmission with Auto/Stick (which makes an automatic behave somewhat like a manual), 18-inch polished aluminum wheels and touring tires and the 3.5-litre V-6 High Output engine.

The AWD Dodge Magnum RT will list for $39,660, the AWD Chrysler 300, when it arrives later this year, will be $33,990.

The AWD Chrysler 300 Touring will be $35,420, the AWD Chrysler 300 Limited model will list for $39,420 and the AWD Chrysler 300C is the big ticket model coming this fall, with a list price of $45,250.