Another Urban Legend

[mpolli]

My neighbor just sent me a "helpful" chain e-mail on the subject of using cruise control in the rain. The gist of it is that if you use cruise control in the rain, and you hit water and hydroplane, that the car can accelerate out of control.

It also claims specifically that "NOTE: Some vehicles (like the Toyota Sienna Limited XLE) will not let you activate the cruise control when the windshield wipers are on"

I am skeptical for several reasons:

1) I have never heard of this and I am reasonably old!

2) Certainly cars with traction control should not have this problem

3) I had a cruise control back in the early 80's and I am pretty sure it could detect an over-revving engine.

Basically I think this is BS. Does anyone have any actual experience with this?

Mike

[Dee8go]

That reminds me of one I heard years ago about Volvos accellerating out of control without any "help" from their drivers. I think there might have been something about that on Sixty Minutes or something. I've never heard of this, though.

[Gurkha]

Originally Posted by Dee8go

That reminds me of one I heard years ago about Volvos accellerating out of control without any "help" from their drivers. I think there might have been something about that on Sixty Minutes or something. I've never heard of this, though.

Wasn't that the Audis in late 80s early 90s?

[Kuan]

The antilock brakes would activate wouldn't it?

[Dee8go]

Originally Posted by Gurkha

Wasn't that the Audis in late 80s early 90s?

Yeah, maybe it WAS Audi. I can't remember for sure. It was one of those ferrin cars . . .

[BAVBMW]

There are several different factors at play here.

First off, most vehicles do not have traction control systems. They're fairly new and only on the higher trim levels for many manufacturers.

Secondly, no, antilock brakes won't do anything. They only act when you are stepping on the brake. If an inattentive driver doesn't hit the brakes, they do nothing. They only help, not replace, the drivers braking efforts.

Thirdly, most cruise systems do not detect an overrev state. In fact, they will cause one. Especially older, 80's vehicles. What happens, basically is if the cruise system detects that the vehicle speed is dropping (let's say you put it in neutral) and applies more throttle to correct (it doesn't know you're in neutral, manuals have clutch switchs in most cases, but automatics have no similar system), there's no load on the engine so it picks up speed at an alarming rate, meanwhile the vehicle is still slowing, so the cruise adds more throttle... You get the picture.

In the case of a slippery road, it's often more the opposite. Once the drive wheels begin slipping, the cruise sees the vehicle speeding up (removing load from the wheels, ie; slip, will cause them to gain speed) so it begins to let off the throttle, this will slow the wheels, but if the vehicle is hydroplaning, it won't neccessarily slow the vehicle. Now when the vehicle reaches an area where traction is availible, the slow moving wheels grab and start to slow whichever end of the vehicle they're on at a faster rate than the vehicle as a whole. See where we have a problem?

Fourthly, you say you've never heard of it? Without going into all the reasons why just because "I've never heard of it" is not a valid argument, I'll just say that perhaps you should read your vehicles owners manuals better, as almost of them mention it.

Yeah, while it's not a death sentence to use cruise in the rain, yes, there is some truth to the stories, it can be hazardous.

MV

[mpolli]

Originally Posted by BAVBMW

Thirdly, most cruise systems do not detect an overrev state. In fact, they will cause one. Especially older, 80's vehicles. What happens, basically is if the cruise system detects that the vehicle speed is dropping (let's say you put it in neutral) and applies more throttle to correct (it doesn't know you're in neutral, manuals have clutch switchs in most cases, but automatics have no similar system), there's no load on the engine so it picks up speed at an alarming rate, meanwhile the vehicle is still slowing, so the cruise adds more throttle... You get the picture.

In the case of a slippery road, it's often more the opposite. Once the drive wheels begin slipping, the cruise sees the vehicle speeding up (removing load from the wheels, ie; slip, will cause them to gain speed) so it begins to let off the throttle, this will slow the wheels, but if the vehicle is hydroplaning, it won't neccessarily slow the vehicle. Now when the vehicle reaches an area where traction is availible, the slow moving wheels grab and start to slow whichever end of the vehicle they're on at a faster rate than the vehicle as a whole. See where we have a problem?

Do you know any of this FOR A FACT. Or are you ASSUMING? I know for a fact that my cruise control from 1983 detected over-revving. I would think this would be a basic safety feature of cruise control systems.

[BAVBMW]

Yes. I know it for a fact. On several mid-eighties products. See, I was in highschool in the nineties, and we all had older cars and an acute lack of common sense so...

Yeah, most cars did not detect an overrev. Lucky were those who had cars that had rev limiters.

Also, I've been a mechanic for years now, and have diagnosed many cruise systems on many makes and models. Most are/were until recent times, stand alone systems that detected very little other than vehicle speed and throttle position.

MV

[MS Fowler]

So the point of this is.....
The DRIVER is responsible for keeping his/ her vehicle under control at all times.

[beevly]

Status: True

http://www.snopes.com/autos/techno/wetroad.asp

[dynalow]

Originally Posted by MS Fowler

So the point of this is.....
The DRIVER is responsible for keeping his/ her vehicle under control at all times.

Xactly. But hey, if some driver or his lawyer can blame any accident on the car design, well, "I'll see you in court".

Fwiw, on a personal level, I don't drive with cruise in the rain. That extra second or two of reaction time in the rain may make a difference, imo.

[Chas H]

The owners manual for both my cars warns against using TC when operating in conditions of deminished traction.

[waybomb]

Hmmmm
I have first hand experience with this in my 1997 C280 Sport.
Headin east on 94, east of Johnson Creek, in a downpour. I had the cruise on. I had it set on 73mph. The tires were in like as new condition.

Came down a gradual hill in the road. Hit the puddle of water at the bottom that was not draining well. The car slowed down quickly, as if I had applied the brakes, the cruise picked up almost just as quickly, and in a fraction of a second, I had started to go sideways. I tapped the stick to get rid of the cruise, and did a nice slow spin, hitting the grassy didvider looking at the opposite direction traffic at a 90 degree angle.

The grassy median in this area, thankfully, was one of the few sections that was relatively flat with the highway, and had no poles or dividers in the middle. The car continued to do a nice slow spin and by the time I was in the middle of the grassy divider, I was pointing in my original direction of travel, and slowing down fast.

I wasn't about to get stuck in the middle, so I gently gassed her and pulled out of the grassy area. My wife about had a heart attack. I had some scratches on the AMGs, and the right inner fender liner that has the air duct in was MIA, but all else was fine. Like it never happened.

I NO LONGER USE CRUISE IN THE RAIN. I don' care what anybody hypothesises.

[Emmerich]

First, anything in a chain letter is a spammer trying to obtain e-mail addresses, so don't forward them!

Second, hydroplaning does not cause wheel speed to increase. When traction is lost, the wheels slip and keep turning while the car slows. The drive wheels are turning at exactly the same RPM as before. Because there is slip, you will normally experience a side slip because both wheels do not lose the same amount of traction and you get a sideways force. The largest force to overcome is the initial slip, once that happens it is easier to maintain slippage.

The effect is the same as if you hydroplaned while normal driving, you as a person know to back off if wheels slip, the cruise control does not. Therefore it is possible you could miss your exit.

[t walgamuth]

It all depends on how the cruise is set up.

I think the biggest danger with the cruise in the rain is if you have a front driver. The rear drive car mentioned above which spun out in the rain must have had some seriously wide tires to hydroplane the rear tires....as the fronts usually squish the water away for the rears.

I had a major tank slapper in my 82 suburban diesel. I was driving from Dearborn to Kalamazoo after visiting the Ford Museum about twenty years ago in a condition of blowing snow. The road remained clear of snow but it was blowing around a lot, so I felt safe driving with the cruise on. I came to a place where there was a bridge over a train track or something and we were in a curve. Unbeknownst to me the pavement over the bridge was coated with black ice. Suddenly the suburban was going sideways. I corrected and it slid back the other direction, I corrected again and it went back the other way further each time.

I had two of my kids, my dad and my brother in the car with me and it was totally silent....the only sound was my hands patting the steering wheel quickly as I spun it back and forth....finally I realized that the cruise was speeding up the rear wheels as the sensor for it was on the front wheels and it was sensing that the car was slowing and so fed the engine more throttle. As soon as I realized this I tapped the brake and the cruise shut off and the suburban immediately straightened out. (It also had positraction which will make the car go sideways in a heart beat in these conditions).

I had never been so far sideways three different directions in a car before. And the the mass of the suburban created additional terror.

We all breathed a big sigh of relief and continued on....of course I had to stop and clean out my britches.

A couple of years ago I got about the same amount sideways three different directions in my SIL's newly purchased Porsche 911, but that had nothing to do with cruise control, just an on ramp which changed from concrete to asphalt and a bit of overapplication of tire gloss by the selling dealer and an overenthusiatic attack of the entrance ramp by yours truly.

I never left the pavement but I had to stop again and clean out my britches.... I could just imagine explaining to my daughter how I had spun their new purchase into the grass and damaged something.

So now I rarely use the cruise under heavy rain conditions and or snow or ice.

And if I do I tend to keep a finger poised over the dis engage button.

Oh yes, cruise control in limited traction conditions can induce some exciting conditions!

Tom W