Originally posted by: Jeff7
Originally posted by: destrekor
:laugh: holy shit
btw
ice everywhere basically means no car will ever have control. It simply means driving on flat surfaces and being more skilled at keeping the car as close to controlled as possible, not that you're ever actually in complete control. 😛
Looks like that area is the opposite of flat, which should give people the idea that they will be sliding until they reach an incline or a fixed, stationary object, if of course they don't just bounce off - like was apparent in that video.
Yup, I've had the misfortune of being out "driving" on an iced-up highway. Traffic slowed to less than a walking pace. I started fishtailing a bit without applying any gas or brake pressure - just the sideways slope of the road was enough to do it.
Brakes or no brakes, unless you've got steel spikes on your tires, you're going to slide on ice like that. Driving skill doesn't matter.
If anyone there had a bag of salt, they might have been able to at least make a few breaks in the ice to stop cars from bouncing around any further.
I'm going to go out on a limb and somewhat, but not completely disagree with you. I disagree in reference to the driving skill. RedSquirrel is correct. You do NOT want to lose the static friction between the ice and the tires, i.e. break loose. The vast vast majority of drivers when skidding on ice will automatically push down harder on their brakes. Wrong decision.
Now, where I agree is that it's very difficult to keep the tires from slipping. Nonetheless, there is a huge difference between the coefficients of static friction rubber on ice and the coefficient of kinetic friction rubber on ice. There is, of course, some variation among different tires, but the coefficient of static friction (when you're driving and the tires aren't slipping) is somewhere around 0.15. Slam on the brakes and keep the tires locked up? How big of a difference does that make? It was a little harder to find a coefficient of kinetic friction for rubber on ice (I have seen the static coefficient many many times so I trust the .15 figure to be a reasonable representation.) But, the only kinetic coefficient I could find was
0.005
That means that a panicked driver who holds the brake down (vast majority of drivers) is going to travel THIRTY times as far before coming to rest on a flat surface covered with ice (so that all of the force stopping the vehicle comes from friction.) Downhill? They're not stopping. Even if that figure of 0.005 is off by a bit, an experienced, skilled driver on ice is going to be able to stop in a small fraction of the distance of the panicked, spike the brakes driver.
Now, watch that Seattle video again. Notice how near the end the one car is able to negotiate the turn. HOW?! Magic tires??! No, the driver was either skilled or else very very lucky. I'd wager more on skilled.
Now, I mostly agree with Jeff7, as a "safe" speed is probably limited to about 5 mph on such road conditions, maybe a little more if you're going straight and aren't going to need to turn (maybe 15ish?). Above that, you're probably screwed. That's not driving, that's carefully maneuvering. Also, the world isn't flat. It doesn't take that much of a slope for it to not matter. The component of gravitational force parallel to the road surface can easily be greater than the maximum static frictional force. (Just a *very* quick calculation, I'm getting between 8 and 9 degrees of slope.)
Turning: centripetal force. The centripetal force is almost exclusively provided by friction between the tires and the ice. Tires are skidding? Forget it. As pointed out above, if they're skidding, there's going to be practically zero frictional forces. Going a little faster as you attempt to go around a corner, say twice as fast? That's 4 times as much force needed to turn. Say hello to the curb.
So, does skill matter? Absolutely. It prevents accidents. But skilled drivers are also smart enough to avoid icy roads and know that they have very very little control over their cars on ice. (Panicked drivers with the brakes slammed on have ZERO control.) But, at low speeds, that little control is often enough to avoid accidents. It's pretty unfortunate too that 4WD drivers think they have more control. No, you have more control over the static friction used to accelerate your vehicle, but the 4WD gives you no advantages when it comes to stopping.
edit: paragraph 3. I meant "30 times as far or until he runs into something bigger than his car. Whichever comes first."
😛
