A colleague passed around an item that told of a woman who had totalled
her car when she hydroplaned with cruise control on. It read in part
Now this makes no sense on the face of it. It wouild seem to me that as
soon as the wheels started spinning, the cruise control would sense the
car going too fast and try slow it down by easing off on the gas.
Besides, once you have lost contact, it cannot matter what the engine
does. No traction, no acceleration. My guess is that she lost
traction, went off a curve and crashed. Or maybe she lost traction on
one side and went off on the other. Is there any possibility the story
is true or was the cop just blowing smoke? To me it has all the earmarks of an urban myth.
Sounds like the description of a perfectly lousy driver to me. Why do they issue licences the these dolts?
“Well officer, I was driving on on a slick highway and didn’t know WTF I was doing so I put it on cruise control because I don’t want to take any responsibility for my ineptitude.”
I’m not against capital punishment, I just think it’s misapplied. This idiot should be hung in the town square.
Well there is a piece of work. We have cars that gain the ability to fly when there is water on the road. I understand the problem is caused when car loses almost all traction which of course instantly makes it accelerate extremely quickly. The problem was carefully documented by drivers who’s cars leapt into the air. They noted the speed on the speedometer didn’t match the speed that they calculated their car was moving using their knowledge of physics.
I am sure that cruise controls aren’t a great idea when there is lots of water on the road. The driver shouldn’t be driving in that style then anyway. Still, I am sure that some cruise controls will disconnect when they sense a rapid change like that and I know ones with automatic traction systems will.
The OP’s question was if the car’s drive wheels would begin spinning and cause the car to hydroplane.
Theoretically, the cruise control maintains a consistant speed to the drive wheels. If you go up a hill and start to slow down, the cruise control will make the car accelerate to try to compensate. Vice-versa on downgrades.
The cruise control relies on a speed sensor, or the actual speedometer cable on older cars to determine how fast the car is going. So if you hit a puddle, it’s not going to make the car try to accelerate.
BUT (yeah, a BIG BUT) when you’re driving in the rain and you hit a puddle and you feel the car start to hydroplane, you instinctively let off the gas, which allows you to regain traction almost immediately. If the cruise control is set, the only way for this to happen is if you tap the brake, which could be disastrous, or flip off the switch to the cruise control. More than likely, you’re not going to react fast enough for the latter to be effective.
I know from experience that driving with the cruise set in the rain can make the car feel totally out of control in some conditions. I haven’t attempted it since I was in my teens after one experience of almost losing control.
While this doesn’t address hydroplaning specifically, this cite recommends not using cruisde control for winter driving, which is also what I’ve been taught:
So basically, the cruise doesn’t sense the increase in speed. Also, in some vehicles, like my truck, the speedometer doesn’t go higher when the wheel spin, it actually drops as the actual vehicle speed does which would cause the cruise control to increase power exacerbating the wheel spin.
Snopes and the Straight Dope don’t have the same goals with this glurge. Snopes merely ignores the text of the message and says that yeah, driving with a cruise control in heavy rain is dangerous. I think we can all agree on that. They don’t address the issue of cars accelerating with no traction and then spontaneously flying into the air. Where is this cruise control speed dial that the police looked at to work out the Scooby Doo physics involved in the story?
It’s a bad idea to use cruise in bad conditions. That much is true. And should be pretty obvious.
I don’t believe that CC will continue to spin the wheels trying to get the car to go faster. It judges it’s speed based on the speed of the drive wheels, engine, transmission and/or a combination thereof.
I put an aftermarket CC on one car I owned. Since it was a manual, it based its speed on engine RPM (don’t shift with it engaged).
I’m curious, what kind of truck?
Someone will be along to clear this up pretty soon I imagine. I say that snoops is not right on the money here.
I could see how the right combination of some tires slipping and some tires having traction might make a car go airborne. For example, you are an idiot driving with the cruise control on in a downpour. You hit a puddle that does not have an edge perpendicular to your direction of travel. One side of your car slows sooner than the other and the car begins to go sideways. The shit has hit the fan and you are now sliding on all 4 tires. Your car slows down since there is no road contact to accelerate against. The car sinks through the puddle and one tire hits first. If you have ever seen NASCAR, a car sliding sideways that suddenly gets traction on one side (the leading side) and rolls over (and over and over and over at 200 MPH). With the cruise control on, the contact tire might be spinning enough to cause the car to lurch forward, but I can’t really fathom a way that the car would actually launch “like and airplane” without accelerating off a high spot or some weird suspension rebound situation. IIRC, planes don’t flip over on takeoff. Of course, I am not a physicist, so I could be completely wrong.
About the Snopes link. They had pretty much what they have now when the above was written. I sent them a link to the thread and a copy of my post. They sent me a note back saying that my explanation was too long. :dubious:
Anyway the last time I participated in a “Is Snopes a valid source” I looked up this article only to find they had changed it, from a gren true to either a white undetermined or a green/red saying that part of it was correct and the rest was false. Now they have gone back to it’s true. Bullshit. If the drive wheels don’t have any traction, the car will not accelerate.
Christ Snopes, pick a side in this arguement and stick to it.
But I guess that was not dramatic enough for 2006, so now
So if the tires are off the ground how can the car accelerate to 10-15kms faster then it was traveling when it had traction on the ground? :smack:
BTW the areodynamic forces on a NASCAR race car are way way higher then they are on a street car at 1/3 that speed.
Interesting site. It confirms that it can be dangerous to use cruise control in wet or especially icy roads, but it also confirms that the post I got was an urban myth. The reason is that one of the sentences I deleted from my quote was repeated word-for word on that site. Except that the incident was said to have taken place in Nova Scotia. Incidentally, one of my sons has a car with automatic traction control and it will turn the cruise control off instantly if it senses loss of traction.
The only way that can be true is if the speedometer is running off different wheels to the drive wheels. IIRC this is true of the old VW campers and Beetles (RWD with the speedo cable hooked to the front wheels), but would be a crazy setup for cruise control. Which doesn’t mean that there isn’t a vehicle somewhere that is built like this…
This was my point in the post I made. I wasn’t aware that any car had ever been built that had the speedometer attached to anything but the transmission. (I realize the newer cars with traction control and ABS have computer controlled systems that know the speed of each wheel, don’t use cables, etc.)
My '75 Chrysler has a speedometer cable that comes out of the transmission into the cruise control and then out of the cruise into the firewall and eventually to the speedometer. A separate accelerator cable comes out of the cruise control and attaches to the linkage at the carburetor.
I know if you accidentally pop it into neutral with the cruise on, the engine will redline. I guess that it senses the drop in speed and adjusts and when the car doesn’t accelerate, it goes to the extreme, just like when ascending a very steep hill, putting the pedal to the floor still might not maintain your speed.
Another thing I didn’t realize was that in the OP, the whole “airborne” thing was actually referring to the car coming off the ground. I just thought it was a “stupidism”. There must’ve been one of those hidden ramps to launch the car that’s only visible for a split second from the first camera angle. If not, we could put the airlines out of business by building a long runway that’ll hold a few inches of water and just drive onto it real fast with the cruise set! My Chrysler has Corinthian Leather [tm]…first class air travel!