[SugarRushMurano]

From Weekly ON SITE MECHANIC
Urban Legend
Article can be found here

Q--Recently, someone sent the following story over the Internet and I was wondering if there is any merit behind the warning about using cruise control in wet or icy conditions?

"Please read this, it could save your life! 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 and Kilgore. It was raining, though not excessive, 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 the 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. 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…."

A--We, too, have gotten this email. Although your car will not take off like an airplane, your wheels could lose traction. At high speeds, the water builds up in front of the tire. But, the tread grooves are there to channel it away allowing the rubber tread blocks to remain in contact with the pavement. When the water is deep and your speed excessive, your car will actually ride on a film of water - especially if your tires are worn

Honestly, you should never use cruise control when driving conditions are not perfect. You have much better control if you apply you own senses when driving

 

[midnitexpress]

haven't tried hydroplaning in the MO yet with Cruise Control on, but in a 'Benz, if the rear wheels start to spin the cruise cuts out. This takes a blink of the eye which was faster than I would be able to react, so I always used the CC during inclement weather, though only on the highway. Haven't had much experience in rain on the highway in the MO yet.

 

[SIM]

Benz and Volvos are designed and built around security. On the Benz, all sorts of indicators and security measures pop up when many dangers are detected. A bulb burns out and there's an indicator in the dash. You don't shut the door properly and an electric motor finished the job by itself. It would cost a lot more to buy a MO if all of these were to be incorporated into it.

But I do wonder why the SE model with the VDC (sensors being already there) does not shut off the cruise when a slip is detected. That would have been so easy to do and IMHO, can easily be retrofited in existing SEs by a master of electronics like Jaak... :2:

 

[hfelknor]

I can't speak to the Murano as I do not know where, and how, the Speed sensing is done. But I suspect that the theory is the SAME.


This whole line of thinking is a bunch of hooey on a "standard" front engine, RWD automobile and I suspect, on a FWD automobile.

The car doesn't know how fast it is going.
There is no GPS sensor, etc.
It only knows how fast "something" is turning.

It only knows how fast the drive wheels are being turned.
On most "standard" cars this is a sensor, or even a physical connection (Speedometer cable) to the output of the transmission.
So, when the output of the transmission is turning a set speed, such as 1000 RPMs, the speedometer is calibrated to read, say 60MPH. (These are not real numbers)
Note that if the car were up on Jack stands and you turned the output of the transmission 1000 RPMs, your speedometer would say 60MPH, your drive wheels would turn the same speed as if you were out on the highway. Exactly the same speed.
Even though the car would be going 0 MPH!

So, when you set the Cruise Control to 60 MPH on this kind of a car, you are saying, I want the transmission output to be 1000 RPMS (And by definition the wheels will turn at a set ratio) WHETHER THEY HAVE TRACTION OR NOT.


So if you are going along at 60 MPH minding your own business, and you hydroplane, your drive wheels WILL NOT GO FASTER.

So, this story, the "troopers" statement, and other stories I have seen like this are so much HOOEY IMO. :2:
It is an urban legend.

BUT I DO agree with Sugar Rush. You should not use CC under unsafe conditions.


Homer


The reason I talked about RWD as being the standard is that this is the setup I was driving the last time I hydroplaned and this is exactly what happened. NOTHING!

 

[Kris]

Aquaplaning (hydroplaning) has nothing to do with cruise control. It is a function of: speed, tires ability to remove water and “thickness of water”. Some factors, such as side wind or road curvature may affect it as well.

Most of all one need to exercise caution (read common sense!) when driving during rain…..

 

[SIM]

Yes, hydroplanning, after the fact that caused it, is riding on a thin layer of water for one or more wheels. What causes it is usually a deeper pothole usually hit by one side of the vehicle, thus inducing a loss of control. Because one side (inside) of the vehicle is meeting a stronger resistance than the other side (outside), the outside moves faster (read wheels spinning faster on the outside).

If both sides of the vehicle hit the same pothole density at the same time, the vehicle will simply slow down and then begin to hydroplan in a straight line until proper contact with the pavement is reestablished, hopefully by lifting the right foot. But then, the rear wheels not yet meeting the resistance would have turned slightly faster than the front wheels.

This resistance being met is usually quite strong and in theory, should momentarily brake the wheel(s) that is (are) meeting it. I never hydroplanned yet with the MO but I did with numerous other vehicles (more often in my Z however )

I suspect that if this resistance from braking occurs stronger on one side or on both front wheels, the AWD will kick in just as if the other side was slipping on ice.

Am I simply all messed up from yesterday's party? :2:

 

[SIM]

BTW my 1990 TT Z accepted to engage in cruise control mode up to 220 km/h which is *really* dangerous! I don't know what speed is the max for the MO's cruise control though. Anything over 120 km/h is quite dangerous IMHO.

 

[seaofdunes]

I have hydroplaned in the mo only once. It was on 287S in extremely heavy rain. The car drove smooth, though the wheel pulled a little to the right (i was in the left lane). The accelerator hit the floor, and then bounced back and it only lasted maybe a second. My Mo doesn't have the VDC, and it is the only time I have ever hydroplaned and no, the CC was not on.

 

[SIM]

You mean that the gas pedal got sucked to the floor and popped back by itself after a sec????

An I thought I was the one drinking serious stuff here!