ddhr.org - Four-wheel drive

Date: 2008 | 02 | 13

Four-wheel drive (4)

Feb 13, 2008

Two thoughts on four-wheel drive:

1. The coefficient of friction is the ratio of the weight of an object to the force required to move the object. For example, if a concrete block weighs 40 lbs and requires a 20-lb force to get it to move, the coefficient of friction between the block and the surface is 20/40 or 0.5.

The coefficient of friction between rubber and ice is somewhere around 0.06. In a vehicle with two driven wheels, the coefficient of friction between the tires and the ice is 0.12. In a vehicle with four driven wheels, it's 0.24. For comparison, the coefficient of friction between rubber and asphalt is around 0.6.

In other words, you'll still slip and slide on messy roads whether you have four-wheel drive or not.

2. I can't find a reference at the moment, but I read recently that people who drive 4WD vehicles are more likely to drive recklessly in hazardous conditions than other people because they incorrectly believe their 4WD vehicle is safer. #travel

Comments

Rus

Feb 13, 2008

In my experience, which did not involve a blackboard, straightedge, chalk and a drawn decline, (in other words not in physics class), 4WD handles differently and very well. Once the driver realizes how it handles differently and still respects that ice and snow are what they are, they will be in better control of their car. I think the more correct statement would be "4WD vehicles are more likely to drive recklessly in hazardous conditions than other people because they overestimate how much more control they have with 4WD."

I used to love driving my Rav4 in the snow, but then I would specifically take the back roads because I don't trust anyone's driving in bad weather. I figured I'd rather slide into a ditch than deal with someone going left of center.

Dave

Feb 13, 2008

Whoa whoa whoa. To be fair, a RAV-4 is a little different than a typical 4WD drive vehicle. Namely, it's smaller and lighter, and I think that has almost more to do with it than how many wheels are driven. My 2WD vehicle performed admirably in the snow yesterday, while a heavier though similarly-sized car in front of me was skidding all over the place.

But yes, I agree. Four-wheel drive causes people to overestimate control.

Rich

Feb 14, 2008

I agree with Rus. I used to drive an Explorer, and in weather like yesterdays, I really noticed a difference. I disagree with your assessment on two points. 1. You seem to dismiss that the difference between a coefficient of friction of 0.06 and 0.24 could help. It's still easy to slide, but I think it gives you just a little more leeway. 2. More importantly, with a 2WD system, generally power is distributed mainly to whichever wheel is encountering the least resistance (traction control can negate this), meaning that if only one of the two wheels that are driving the car is on ice, that wheel will spin out. With 4wd, the opposite is the case (usually) - if any one wheel still has traction, power is redirected to that wheel, and you keep going without sliding.
I especially miss my explorer since sliding off the road in my cavalier yesterday. :(

Wendy

Feb 15, 2008

I'm going to have to agree with Rus' statement: “4WD vehicles are more likely to drive recklessly in hazardous conditions than other people because they overestimate how much more control they have with 4WD.”