When deciding between 4WD and 2WD, ignore Internet

Dear Car Talk:

My 2020 Chevy Silverado has a selectable four-wheeldrive system. There are four options: “Auto,” “2WD High,” “4WD High,” and “4WD Low.”

The dealer says the 4WD High and Low are only to be used when it’s slick out. But, I see some people on Internet forums who say it should be used no matter the conditions.

Sometimes, I do put it in “4WD High” and forget to switch back. Then I discover I’ve been driving in that mode for several days. So, once and for all, is it OK to drive in that mode all the time?

— Mark

No. But it’s confusing, Mark. And, as with most things, the Internet — with its opinions from the full range of the human intelligence spectrum — tends to make it more confusing.

Here’s the answer: You can use either “2WD” or “Auto” all the time. If you don’t have any need for extra traction, using “2WD”

may save a tiny bit of money on fuel and possibly some wear and tear on the fourwheel-drive components.

“Auto” in your truck operates in two-wheel drive by default. And, when it senses a loss of traction, it automatically adds power to the other wheels. So, “Auto” is safe to use all the time, and that would be my default mode.

“4WD Low” and “4WD High” are not safe to use on dry roads. They’re only for while you’re actually driving on slippery terrain. Those two modes lock your center differential to give you maximum traction for when you’re stuck or in snow, sand or mud.

The problem is that when the center differential is locked, the wheels aren’t able to turn at different speeds.

When is that important? When you’re turning. When you take a turn, each wheel actually spins at a different speed. The inside wheels don’t travel as far as the outside wheels on a turn, so they turn slower.

If they’re forced to turn at the same speed, one of them has to drag or scrub along the pavement, leading to unsafe handling and possibly flipping over.

Of course, that doesn’t matter if you’re in sand or snow, because the wheels can slide. But, if you’re in “4WD” at highway speed on a dry road and take a curve, you could very well be in trouble.

So, if you have no need for extra traction, use twowheel drive. If you sometimes need the extra traction, or just never want to think about this topic again, use “Auto.” And save the other two modes for the next great olive oil spill.