# Cruise control and hydroplaining **URL:** \ **Category:** Factual Questions\ **Created:** [January 7, 2006, 12:58am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826 "2006-01-07T00:58:46Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [January 7, 2006, 12:58am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/1 "2006-01-07T00:58:46Z")
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 > [@](#): > > NEVER DRIVE IN THE RAIN WITH YOUR CRUISE CONTROL ON. > > She had thought she was being cautious by setting thecruise control > and maintaining a safe consistent speed in the rain, but the highway > patrolman told her that if the cruise control is on and your car begins > to hydroplane-- when your tires lose contact with the pavement, your car > will accelerate to a higher rate of speed and you take off like an > airplane. She told the patrolman that was exactly what had occurred. > The highway patrol estimated her car was actually traveling through the > air at 10 to 15 Kms per hour faster than the speed set on the cruise > control. 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. ---
**Author:** ![R.P.McMurphy](https://avatars.discourse-cdn.com/v4/letter/r/7993a0/32.png) [@R.P.McMurphy](https://boards.straightdope.com/u/R.P.McMurphy)\ **Post date:** [January 7, 2006, 1:05am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/2 "2006-01-07T01:05:43Z")
What kind of car and what year? 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. ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [January 7, 2006, 1:08am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/3 "2006-01-07T01:08:53Z")
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. ---
**Author:** ![jasonh300](https://avatars.discourse-cdn.com/v4/letter/j/46a35a/32.png) [@jasonh300](https://boards.straightdope.com/u/jasonh300)\ **Post date:** [January 7, 2006, 1:12am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/4 "2006-01-07T01:12:32Z")
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. ---
**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\ **Post date:** [January 7, 2006, 1:14am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/5 "2006-01-07T01:14:05Z")
[Snopes](http://www.snopes.com/autos/techno/wetroad.asp) says TRUE. ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [January 7, 2006, 1:16am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/6 "2006-01-07T01:16:03Z")
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: From the [British Columiba Ministry of Transportation](http://www.th.gov.bc.ca/popular-topics/driver_info/winter/winrd1.htm) > [@](#): > > **Turn off your cruise control** > > When the road is slippery, turn off your cruise control system. Snow, ice, slush or even rain can cause wheel-spin and loss of control. > > The only way to stop this wheel-spin and maintain control is to immediately reduce power. However, an activated cruise control system will continue to apply power, keeping the wheels spinning. By the time you disengage the cruise control, you may have lost control 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. ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [January 7, 2006, 1:22am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/7 "2006-01-07T01:22:57Z")
> [@don't ask](#): > > [Snopes](http://www.snopes.com/autos/techno/wetroad.asp) says TRUE. 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? ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [January 7, 2006, 1:24am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/8 "2006-01-07T01:24:43Z")
> [@St. Urho](#): > > 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. Systems that are advanced enough to account for differential wheel traction also have cruise controls that take that type of thing into account too. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [January 7, 2006, 1:37am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/9 "2006-01-07T01:37:01Z")
Well, I call bullshit. Sort of. 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). > [@St. Urho](#): > > the speedometer doesn’t go higher when the wheel spin 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. ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [January 7, 2006, 1:46am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/10 "2006-01-07T01:46:56Z")
> [@enipla](#): > > I don’t believe that CC will continue to spin the wheels trying to get the car to go faster. Let’s not get this started. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [January 7, 2006, 1:50am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/11 "2006-01-07T01:50:39Z")
> [@Shagnasty](#): > > Let’s not get this started. Oh God. :smack: ---
**Author:** ![xbuckeye](https://avatars.discourse-cdn.com/v4/letter/x/9e8a1a/32.png) [@xbuckeye](https://boards.straightdope.com/u/xbuckeye)\ **Post date:** [January 7, 2006, 1:51am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/12 "2006-01-07T01:51:33Z")
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. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 7, 2006, 2:15am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/13 "2006-01-07T02:15:34Z")
We did [this exact e mail a while back](http://boards.straightdope.com/sdmb/showthread.php?t=147788&highlight=hydroplaning) Here is what I wrote then, and it still applies. > [@Rick](#): > > > [@Meatros](#): > > > > He said if you did and hydroplaned (which I did) that when your tires were off the road your car would accelerate to a high rate of speed (which it did). You don’t have much, if any control when you hydroplane, but you are totally in the hands of God when the car accelerates. I took off like I was in an airplane. I’m so thankful I made it through that ordeal. Please pass the word around about not using cruise control when the pavement is wet or icy. The highway patrolman said this should be on the sun-visor with the warning about air-bags > > OK let’s take this apart one absurd sentence at a time. > (For the record I do qualify as an expert, as I teach this stuff for a car company) > > > [@](#): > > > > He said if you did and hydroplaned (which I did) that when your tires were off the road your car would accelerate to a high rate of speed (which it did). > > OK I call bullshit. Hydroplaning is defined as when a tire has a thin layer of water between it and the road resulting in a zero traction condition. This is why BTW good tires are so important in the rain. Deep tread can channel away more water, and are therefore more resistant to hydroplaning. Anyway back to the quote. If the drive tires have NO traction (they are off the ground after all, being supported by a thin sheet of water) then how in the name of all things automotive can the car accelerate? The car has NO traction. No traction= no acceleration. Also for the record, when you are hydroplaning you have no steering and until your tires regain touch with Mother Earth no brakes. Now the tires can (and may) accelerate, but since the tires aren’t on the ground, Mr. Newton gets some time off. > > > [@](#): > > > > You don’t have much, if any control when you hydroplane, but you are totally in the hands of God when the car accelerates. I took off like I was in an airplane. > > Up until the word hydroplane the sentence is correct, and quite possibly understating the effects of hydroplaning. However after the comma I call double bullshit. As I have explained with no traction you cannot have acceleration. > > Now a word about how cruise control units work. In most if not all modern cars the cruise gets a vehicle speed signal electrically from either the vehicle speed sensor or possibly the ABS system (after all ABS knows the speed of all the wheels) or possibly as a truput from the speedometer. I am unaware of any car that still uses a speedo cable, there may be one but I sure don’t know of it. The cruise unit uses this speed signal to regulate the throttle either open or close to maintain the set speed. If the tires were to lose traction, then any small movement of the throttle would result in a huge change in engine RPM, however no change in vehicle speed (No traction = no acceleration) But wait you say I can press down on the gas pedal and only cause a 100 RPM gain, why does the crusie casue the engine to race? Simple, a movement on the throttle so small that only causes a 100 RPM shift in neutral would not be noticed when the cruise is set. The cruise makes much coarser adjustments. > At least some of the cars on the road have safeguards built into the cruise unit. for the last 12 years the cars I work and teach on have the following safety disconnects > > 1. Brake pedal depressed (the usual way to disengage cruise) > 2. acceleration of the wheels exceed a predetermined rate (this would disconnect the cruise if the car hydroplaned, or if the cruise control was set while a technician had the car on a rack with the wheels in the air. The designers know exactly how fast a car can accelerate, and any observed acceleration of the wheels above that rate would cause a disengagement. > 3. If the unit says Hi Opal! this will cause a disengagement > 4. the tires slow down beyond a predetermined rate (In case the brake pedal switch is dead, this is a backup.) > 5. Transmission shifted to neutral (or in the case of a stick, the clutch pedal depressed (this addresses what happened to Gilded Lily) > 6. actual speed is less than 75% of actual speed (hey if the cruise can’t keep the car near the set speed, they want you driving) > 7. abnormal speed signal (unit does not like the signal and therefore will refuse to operate) > > On the older cruise systems If a cruise control was inadvertently set while the car was on the rack with the wheels off the ground the engine will go to redline in nothing flat. This is due to there not being any drag on the driveline. A very small application of throttle will do it. This is the same that would happen if cruise were set and the car hydroplaned, the tire would start to slow down and the cruise (thinking the car was slowing) would open the throttle, causing the wheels to spin at very high speed. This could (and probably would) cause the driver to shit a brick. However it would not cause the car to accelerate, as the tires have no traction. Same thing would happen if the car were to be shifted into neutral, car slows down, CC opens throttle engine go to redline, gets driver’s attention. > So what happens when your tires regain traction wouldn’t that cause the car to take off like a shot? IMHO no. Let say that we jack up the back of a RWD car (could be FWD, but RWD is easier to explain) with a floor jack. Tires are off the ground. You get in and press the throttle gently until the car is registering say 80 MPH. You probably have the throttle pressed down somewhere between 1/4-1/2 of an inch to get the wheels turning at this speed. If I were to release the floor jack and drop the drive wheels back on the ground. The tires would probably chirp and impart a couple of miles per hour to the car and then the tires and the ground would be at zero slip and then the car will accelerate at the same rate it would with 1/4"-1/2" of throttle because, after all, you only have the throttle pushed down that far. > Now with all of that said I would agree that using cruise control in poor weather is probably not a Nobel prize winning idea. When the weather is truly crappy you need to be in touch and in control of your car. When things go stupid, they can go real stupid real quick. Driving with cruise control tends to keep you away from one aspect of the driving experience and could lead to an accident due to a fraction of a second of inattention. 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. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [January 7, 2006, 2:31am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/14 "2006-01-07T02:31:50Z")
> [@xbuckeye](#): > > 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. Notice how this piece of crap has evolved. > [@piece of crap from 2002](#): > > I took off like I was in an airplane. But I guess that was not dramatic enough for 2006, so now > [@even crapier piece of crap from 2006](#): > > and you take off like an > airplane. She told the patrolman that was exactly what had occurred. > The highway patrol estimated her car was actually traveling through the > air at 10 to 15 Kms per hour faster than the speed set on the cruise > control. 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. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [January 7, 2006, 4:11am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/15 "2006-01-07T04:11:10Z")
> [@don't ask](#): > > [Snopes](http://www.snopes.com/autos/techno/wetroad.asp) says TRUE. 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. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [January 7, 2006, 8:34am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/16 "2006-01-07T08:34:52Z")
Rick, you are much more patient that I would be… ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\ **Post date:** [January 7, 2006, 8:38am UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/17 "2006-01-07T08:38:00Z")
> [@St. Urho](#): > > 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. 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… ---
**Author:** ![jasonh300](https://avatars.discourse-cdn.com/v4/letter/j/46a35a/32.png) [@jasonh300](https://boards.straightdope.com/u/jasonh300)\ **Post date:** [January 7, 2006, 3:30pm UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/18 "2006-01-07T15:30:42Z")
> [@matt](#): > > 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! ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [January 7, 2006, 11:18pm UTC](https://boards.straightdope.com/t/cruise-control-and-hydroplaining/338826/19 "2006-01-07T23:18:18Z")
> [@enipla](#): > > I’m curious, what kind of truck? It’s a 1993 Nissan Pickup, 4x4.