Dear Tom and Ray:

My daughter just purchased a used 2004 Honda CR-V with four-wheel drive. My question is: How do you use the four-wheel drive effectively? When do you turn on four-wheel drive, and when do you turn it off? Thanks.

-- Claudine

TOM: There are several types of four-wheel-drive systems, Claudine. Your daughter has the best kind -- it's completely automatic. All she has to do is ignore it.

RAY: Like I try to do with my brother.

TOM: Some, mostly older, four-wheel-drive systems require the driver to turn them on and off with a button or a lever. And while some hard-core off-roading nerds and snowplow drivers may still want that system, most of us are glad it's going the way of Miley Cyrus' good-girl image.

RAY: The problem with a manually engaged four-wheel-drive system is that if you engage it at the wrong time, like on dry roads at higher speeds, you can cause the wheels to bind up, and then you can lose control of the vehicle. It can be very dangerous. And even many people who own vehicles with these systems don't know how to use them properly.

TOM: Fortunately, now most cars and even most SUVs come with what we call "all-wheel drive" (Honda calls it "real-time four-wheel drive," and some manufacturers have different brand names for it). Mechanically, they work in different ways. But they all have one thing in common: The car figures out how much power to send to each wheel on a second-by-second basis, and does it without you having to do anything.

RAY: It's not only a much safer system, but it's more effective in everyday road driving, too. Like lots of systems on your car these days, a computer can detect the need for an action, and turn stuff on and off a lot faster, and more efficiently, than you or I can.

TOM: There are some maintenance issues your daughter should be aware of, like changing the CR-V's rear differential fluid every 30,000 miles (and you might want to do that soon, since you don't know whether the previous owner did it). But other than that, she can just forget she even has all-wheel drive and just drive the car.