Getting a grip on traction systems

Are you like reader Don Roth, who’s curious why some vehicles are advertised as having all-wheel drive and some have four-wheel drive?Roth, who sent an e-mail, wonders if there’s any difference.

It’s an excellent question and a timely one since more Americans than ever are buying vehicles that promise some kind of traction for all four wheels.But many consumers don’t know what they’re getting for their money.

Today’s increasingly sophisticated electronics on cars, trucks and sport utility vehicles mean that there’s a variety of traction-enhancing systems out there, and they don’t necessarily operate the same way and don’t have the same kind of capability.

Fancy marketing names add to the confusion.Generally, both “four-wheel drive” and “all-wheel drive” are labels that indicate vehicles that provide power to both front and rear axles at the same time. But this doesn’t always mean that power goes to all four wheels all the time.

For example, the Rock-Trac system in the four-wheel-drive 2007 Jeep Wrangler Rubicon operates part-time and requires a driver to manually engage it — either in “high” or “low” four-wheel-drive mode — via a gearshifter in the center console.

Note that both high and low modes of four-wheel drive in the Wrangler Rubicon are designed for strenuous situations, not for everyday driving on dry pavement.

So when a Wrangler Rubicon driver travels on clear concrete or asphalt on a city street or highway, he or she is in a two-wheel-drive vehicle.

Basically, “four-wheel drive” — also sometimes called 4X4 — has been found over the years primarily on rugged vehicles like pickup trucks and SUVs where a transfer case can transfer power between front and rear axles.

And, these four-wheel-drive systems can include extra-low gearing for rugged off-roading, churning tires through thick mud and deep snow and for rock-climbing.

Meantime, “all-wheel drive” has been a label often found on vehicles such as sedans and wagons that didn’t necessarily need the serious four-wheel travel of a truck or SUV.All-wheel-drive vehicles still add four-wheel traction but generally don’t include low engine speed gearing for slow-speed, rigorous, off-road travel.

Additionally, all-wheel-drive vehicles can use other devices — such as a viscous coupling or multi-plate clutch — between the front and rear axles, not a durable transfer case, to transfer power front and rear.

As if all this isn’t complicated enough, consumers need to look beyond the kind of vehicle they’re buying and the name of the drive system to know what they’re really getting.

They need to dig in and find out exactly how the system works and when it operates.

The reason: Automotive advancements, particularly in electronics, are adding layers of new features to what used to be straightforward four- and all-wheel-drive systems.

For example, many vehicles now can operate as two-wheel-drivers but carry clutch pack couplings that can engage, when needed, for four-wheel power. And this engagement can be done automatically.Additionally, the power sent to the additional wheel axle may or may not be equal to that going to the initial powered axle.

An example is the Suzuki SX4, which ranks as the lowest-priced 2007 vehicle with all-wheel drive.

Starting manufacturer’s suggested retail price, including destination charge, for an SX4 is $15,594 and includes all-wheel drive standard.

The base SX4 is a five-passenger, small hatchback with 143-horsepower, four-cylinder engine and manual transmission.

The SX4 system, controlled by a switch on the console, can be set for fuel-efficient front-wheel drive only, automatic all-wheel drive that kicks in on its own whenever the need for extra traction is detected, or all-wheel-drive lock.In the latter modes, power transfer to the rear axle can range up to 50 percent of what’s going to the front.

The good news from all this complexity is the fact that the newer drive systems are being developed at lower cost so even lower-priced vehicles that wouldn’t have had all-wheel drive before now can offer it.

But know that sometimes there can be a lag before traction is transferred to the additional axle if the system is designed so that it has to detect wheelspin first.

Also, look at how much these systems add to the price of your vehicle and try to gauge how much use — and peace of mind — you will get from them.