Using cruise control in the rain

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JerArdra

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ALL,

I wonder about this.  Do you folks think it's true or a internet hoax?

JerryF
________________________________

    A 36 year old female had an accident several weeks ago  and totaled her car.
    A resident of Kilgore , Texas , she was traveling between Gladewater & Kilgore. It was raining, though not excessively, when her car suddenly began  to hydroplane and literally flew through the air.  She was not seriously injured but very stunned at  the sudden occurrence!

    When she explained  to a highway patrolman what had happened, he told her something that every driver should know - NEVER DRIVE IN THE  RAIN WITH YOUR CRUISE CONTROL ON. She had thought she was being cautious by setting the cruise control  and maintaining a safe consistent speed in the rain.

    In fact, the highway patrolman told her, 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 patrolman said this warning should be listed, on the driver's seat sun visor - NEVER USE THE CRUISE CONTROL WHEN THE  PAVEMENT IS WET OR ICY along with the airbag warning. We  tell our teenagers to set the cruise control and drive a  safe speed - but we don't tell them to use the cruise control only when the pavement is dry.

    The  only person the accident victim found who knew this (besides the patrolman), was a man who had had a similar accident, totaled his car, and sustained severe  injuries.

    INOTE: For this reason, some vehicles do not permit you to set the cruise control when
    the windshield wipers are on. The Toyota Sienna Limited XL E is one of them.
 
JerArdra said:
I wonder about this.  Do you folks think it's true or a internet hoax?

Jerry

Are you talking about the warning not to use the cruise in wet weather or the specific story. Most, if not all, driver's manuals contain a warning not to use the cruise control in wet conditions, as discussed in the article.
 
That advice has always bothered me.  The cruise control senses the speed not through any actual speed measurement, but through the tire rotation, usually through the driveshaft RPMs to the wheel.  If the wheels start to spin, as they will when hydroplaning, the speed sensed by the cruise control will show an increase, and the cruise control will react to reduce the sensed speed by decreasing the throttle, exactly what should be done in those circumstances.  I drove for many years in snow and heavy rain with the cruise control on and saw it behave exactly as I expected.  The cruise control would react much faster than I ever could in reducing the throttle, thus removing power from the drive wheels and allowing me to keep control of the vehicle.
 
Ned said:
That advice has always bothered me.  The cruise control senses the speed not through any actual speed measurement, but through the tire rotation, usually through the driveshaft RPMs to the wheel.  If the wheels start to spin, as they will when hydroplaning, the speed sensed by the cruise control will show an increase, and the cruise control will react to reduce the sensed speed by decreasing the throttle, exactly what should be done in those circumstances.  I drove for many years in snow and heavy rain with the cruise control on and saw it behave exactly as I expected.  The cruise control would react much faster than I ever could in reducing the throttle, thus removing power from the drive wheels and allowing me to keep control of the vehicle.

Ned

But what happens when the wheel gets traction again? The cruise applies power to get back up to speed and you go into a spin. Also, if you start hydroplaning, taking your foot off the throttle (or having the cruise cut off) you have a good chance of going into a spin. When you start to hydroplane, you don't want to upset the car handling. I'd stay with turning it off.
 
I too have used the Cruise in wet conditions for years.  However I do slow down the unit immediately and reset the cruise.  Just my way.
 
Ok, cruise control primer  There are basically 3 ways cruise controls work. NOTE that there are variations on this, I've installed many cruise controls, trouble shot them and have one in the shop just now.

First they must have a way of measuring the speed of the vehicle, there are basically two ways of doing this, One is to measiure engine speed (Tach) and this works very well with stick shift and with lockable Torque converters .

In a hydroplane this system will slow down due to reduced slip in the troque converter and transmission.

The better method, and the one universally used, far as I know, today is to measure the vehicle speed via either the vehicle speed sensor or a secondary speed sensor (Normally magnets attached to the drive shaft)

Now, years and years ago there was a car that measured it's speed via one of the front tires.  On this car, an import, if the rear wheels broke free and spun had they had cruise controls then, (they did not) the car would have tried to accelerate.  However today the speed sensor is part of the transmission assembly, far as I know all American cars were made this way.  So if the rear wheels were to break free the cruise would actually throttle down to keep them turning at the same speed.

Thus, the story is a myth. Pure and simple.. It is a myth.

IT does not try to make the car go the same speed, it makes the DRIVE SHAFT go the same speed.

That said, it's not a good idea to run on less than ideal roads with cruise control due to the fact that should stuff happen, it will take a bit longer to release the engine and slow you down since in normal driving the engine starts to slow as soon as you LIFT your foot and under "Auto-pilot" the engine does not slow till you PRESS the brake pedal.  That short delay can make a big difference in the stopping distance... Not so much when it's clear and dry, but on rain or ice.. Much bigger difference.


Though... For a police officer who is not a mechanic and who not done Cruise control installs, or at least read the manual, to tell someone something which is less than accurate.... That I can believe, easily.

I used to dispatch cops after all.

 
And being even further intruigued, I think I have to disagree with the Snopes article as well.  Now this next article doesn't confirm for sure what John is saying, but still, in reading this, one must conclude that if an automobile starts to accelerate, even at the instant the wheels lose traction and spin out of control, the cruise control is still going to slow down in order to attempt to maintain the set speed.  It will be default probably spin the wheels faster, but so would a person with his foot on the pedal.  It's a matter of reaction time.  Which is faster...that's something for the Mythbusters to determine (hmmmmm, an idea for an upcoming show??).

http://auto.howstuffworks.com/cruise-control.htm
 
And after doing just a little more research (on the Mythbusters site of course), this really does seem to be a myth debunked already.  They showed e-mails from at least three different places (in Canada and Austrailia even), and the cruise control will not do what this says.  It would be interesting to see it finally put to rest though.
 
To me the issue is whether I want me or an external system with unknown parameters managing my speed/acceleration/deceleration in potentially dicey conditions. A cruise control is not always very sophisticated in its speed management (I think we've all seen them do seemingly odd things at times), especially the older or less expensive systems.  And the owner manuals of my last three cars did indeed caution against using cruise in wet, ice and snow.

I'll stick with my own foot, thank you.
 
I agree with RV Roamer.  I will choose myself over a computer to control my vehicle.  Just think at how often your home or office computer does not do things as expected.  Also, the cruise control does not have eyes, I see the patch of ice or water puddle before I drive through it, I can the throttle accordingly ahead of time and be proactive, while the cruise control is reactive.
 
There is one system where the cruise can cause the car to suddenly accelerate.. As i said, I've installed and trouble shot quite a few systems on various cars

One way of sensing speed is to attach a couple of small magents to the drive shaft and put a pick up coil near them, as the shaft turns the magnet/coil combination becomes an electric generator.

Two cycles per revolution.

If you are running oh, say 60 MPH on cruise (won't happen below 50-70 MPH depending on the control) and loose one magnet, then the control sees that the car's speed has suddenly halved.

If it's set to drop out (not work) at speeds below 30 MPH then if you are going over 60 it will attempt to accelerate (to 120+)

If you are going 50, however, it says "oh, 25mph,  BYE" and goes into standby.

But that is the ONLY case where it will cause sudden acceleration.. And any time you press even slightly on the brakes in a properly designed system it drops out, NOW. 

Again, there are two ways this happens,  A cheap system uses one, detects the brake lights  Actually reads the voltage across the brake light switch and if present,,, (Meaning fuses, and at least one bulb are good, switch is open) it works, if not present (meaning either fuse or all bulbs are burned out or switch is closed) it cuts out.

The 2nd system (Most of the ones I installed had this) adds a vacuum line to the  brake pedal and a "Dump valve" (Gate type valve) when you hit the brakes the valve "Dumps" the vacuum (Allows a whole lot of air to enter) the line to this valve is like 2x the diamater of the vacuum supply (4x the cross section) so it drops out the vacuum solenoid (Actual control) with out a doubt.

Not all systems have this feature though.  Some just rely on the light switch.  And other sensors and switches (one is a "Sudden stop" switch)  most of the cut-outs are right hard to fail and most of them fail safe if they do fail.
 

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