Monday, December 15, 2003
The Physics of 4 Wheel Drive and Snow
Repeat after me: 4 wheel "go" does not equal 4 wheel stop.
A quick rant to explain something to you S.U.V. Drivers, most of whom are clueless menaces on the road. I say most, rather than all, on the statistical possibility that one of you has some intelligence and driving skills. So far, this assumption has proven excessively optimistic, but hey -- I'm a positive kinda guy.
In New York, we got hit with a surprise snowstorm Sunday (it moved up from the South unexpectedly fast). We drove back from the East End of Long Island Sunday morning as the snow was coming down pretty fast. I was driving the front wheel-drive, manual transmission car (as opposed to our real wheel cars), so traction was not a problem.
On the LIE, snow accumulation was about 4 inches. By staying in the center of the middle or right lanes where traffic was heaviest, you could make sure your tires were, for the most part, in contact with actual pavement, as opposed to the white stuff. The left lane and the HOV lanes were less travelled and had a few inches of snow covering them.
Here's where things got interesting: Many S.U.V.s and quite few Audi Quattros were hauling ass along the left lanes. I may have a heavy right foot, but I do not go 70 in the snow -- these idiots did. We got to witness a dozen or so fender benders along the way 60 mile trip home: The most memorable was seeing the results of a Nissan SUV spin out, and in an unrelated accident, watching in more or less slow motion, a Hummer (!) careening into the guard rail. (Seriously, how bad a driver must you be to slam the "vehicle that can go anywhere and do anything" into a wall?)
Here's the physics of the situation: 4 wheel drive is your method of locomotion. It's how you go. But here's the -- apparently -- unknown secret: It has absolutely nothing to do with how you stop; That's an entirely different system within your automobile.
But 4 wheel go does not equal 4 wheel stop. It has no impact on halting your momentum. Can you comprehend that? Oh, sure, if you drive a stick -- and downshift properly -- in some situations, you can use the engine to control wheel slip and improve control. But seriously, how many SUV owners drive sticks? And of those who do, how many of them know how to drive? Too few. Perhaps that's why I didn't see any of the Audis in accidents -- they sell a lot of 5 speeds manuals, and Audi owners have a rep for knowing how to drive. But I digress.
If anything, 4 wheel drive merely allows you to get yourself into more dangerous situations. We saw a Porsche 911 fishtailing all over the road. He was aware of his limitations in the snow and was going 30 mph. His torquey, rear wheel drive system had little in the way of traction in the snow -- and he knew it. He crept along in the right lane and still ran into some trouble. (On the other hand, I drove our rear wheel drive SLK home from White Plains Christmas Day 2002 in 6 inches of snow -- it took 3 and half hours versus the usual 60 minutes. I had no problem, but that's mostly because I am not an idiot.)
Now back to our 70 mph snow fools: In the event of loss of traction -- not too hard to imagine in 4 inches of snow -- you are merely a two ton hunk of steel sliding across a frictionless surface until you either regain directional control or run into some mass which stops you. Your Anti-Lock Brake System (ABS) is useless when your tires cannot make contact with the pavement. Modulating brake lock up when snowplaning on a 2 inch cushion of white stuff does you no good whatsoever. The technical term for this phenomena is called "Wheeeeeeeeeeeeeee!"
A message to you SUV (and all wheel drive) owners: Understand the limits of your vehicle. Learn to drive in inclement weather. You'll be doing your families, and the people you share the roads with, a huge favor.
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