Not Too Bad. One Question. If Something’s Breaking Loose (Spinning Faster?), What Happens To The Differential Part Of the Equation Which Lets One Wheel Spin Twice As Fast As The One With Traction?
Think: Stuck, with one wheel on dry concrete, one on ice. Dry wheel = no power. Icy wheel = z z z z z z z z zing.
Think: "If only one drive wheel breaks loose, the other will maintain proper speed."
Rather: If only one drive wheel breaks loose, it will spin up to twice as fast as the other which is getting traction and losing applied power. The Slipping wheel accelerates. The gripping wheel therefore decelerates.
Allow me to clarify: Neither wheel will be stopped in the hydroplaning scenario, nor would the cruise control allow double speed of the driven wheel.
Again, I contend the “accelerating out of control” is all matter of perception. Without cruise control engaged, we let off on the gas at the first sign of hydroplaning (if we’re paying attention!), and the car slows very perceptibly. With cruise, we aren’t affecting speed in the accustomed way, so it can seem we are speeding up.
What we need is a car with cruise control, an empty airport runway, a water tanker, and a radar gun. Mythbusters, anyone?
I’ve Got Cruise Control And A Radar Gun.
We need a vacant airport and some rain, lots of rain.
Are you going to call the show?
NYBo, Have You Read CSA’s Believe It Or Not? Wheels Stop Turning At Highway Speed In The Wet. Trust me on this one. I was there.
Whenever the car loses speed with the cruise control on, the cruise control will try to recover it. It doesn’t have to be water, it can be a hill.
Cruise control can’t tell that the road is slippery. If your tires don’t have any grip at the speed the car is traveling, the worst thing you could do is try to maintain that speed. The cruise control will stupidly do what a driver would not.
When the cruise control opens the throttle and the tires are spinning freely they will go a lot faster than the cruise control can react to. The vacuum diaphragm can’t bleed off fast enough. It makes for a gentler effect on dry roads but you don’t want that effect in zero traction conditions.
It takes my aftermarket system about five seconds to let go when I just turn it off. Nice, huh?
Only if they agree to let us be on the show!
Anyway, maybe this will finally debunk this: It appears that all these explanations of how the car should suddenly accelerate are ignoring what hydroplaning is. When a vehicle hydroplanes, ALL tires have lost traction and the car is skating on a film of water. Even if the the driven wheel(s) were to spin faster than the cruise control setting (which I still contend won’t happen if all wheels have no traction), it won’t matter because by definition in this situation, it/they has/have no traction.
However, it is still a very bad idea to use cruise control in bad weather.
“When a vehicle hydroplanes, ALL tires have lost traction and the car is skating on a film of water.”
Where did you get your definition? Why can’t it be one, two, or three tires?
The sudden surge of acceleration doesn’t nessesarily happen while the tires are hydroplaning. It happens when the car transitions back to a part of the road that is standing water free and suddenly there is traction for the driving wheels that are already turning faster than the road speed.
The sudden surge of acceleration is the car trying to get back to its cruise contol setting after it gradually slowed down from hydroplaning.
Hydroplaning is not an all or nothing phenomenon. There are speeds where the tires hydroplane just enough to lose traction at full throttle but get off the gas and they grip again.
Ah, a very good point. I was assuming the contention was that the car would magically accelerate ABOVE the speed set on the cruise control. But the chain letter isn’t really specific on that point.
– regardless of all our debate, a final lesson here. —
Cruise control is not auto-pilot.
You MUST remain an active participant in your drive. Pay attention. Know, and continually assess the condintions.
The last sentence seems to say that there can be contact with the road and still have hydroplaning exist. I don’t see whee it says that losing contact with all four wheels is required for hydroplaning. Just a loss of contact, even partial, for any wheels.
It seems to me that it is progressively worse as you lose wheel contact, but one wheel spinning on top of the puddle still qualifies. Also in the last paragraph they say thet letting off the gas without using the brakes is the best way to regain control. Since cruise control won’t do this on it’s own, a driver is asking for trouble by using CC. The alernatives are to brake to turn it off (not recommended) let it run (not recommended) or turn it off with your hand controls. Since it may require removing a hand from the wheel to turn it off, I wouldn’t recommend this, either.
Maybe we just shouldn’t use CC when the roads are wet. I suspect that the odds are that you won’t have a problem, but the odds of having one are substntally higher if you use it on wet roads.
Ok - let’s all get on the same page - as someone else suggested, this is a perfect Myth Busters project! I’m forwarding this on. If anyone has connections, please use them. We could truly do a lot of good public education with this one.
By the way, I think the Tappet Brothers would be great guests for this segment!
Here’s the Mythbuster’s link: http://dsc.discovery.com/fansites/mythbusters/talk/talk.html
“I was assuming the contention was that the car would magically accelerate ABOVE the speed set on the cruise control.”
If the differential allows the drive wheels to turn independently, Why wouldn’t the wheel that just lost traction spin faster? Without friction, it should. Whether it would correct the error is a function of whether the CC monitors the wheel that’s spinning or not. If it monitors the drive shaft and one wheel is still firmly in the road, how would CC know that a wheel is spinning out of control?