Killer Cruise Controls?    rev.02.02.2007 Back to Lessons

Kathleen found this at
>  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 hydro-plane 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 hydro-plane, 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 
> 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.
> If you send this to 15 people and only one of them doesn't know about 
> this, then it was all worth it.
> You might have saved a life.
> NOTE:  Some vehicles when the windshield wipers are on, you cannot set 
> the cruise control.

Well, I don't believe it, and here's why.... Write me if you think I'm wrong.

I don't think it's true, and I still don't.

Cars don't tend to work that way, and I still think this is folklore and won't forward it to anyone. Though I did forward it back to Barbara at because the last line is new, and I'd never heard that before!

Cruise controls try to keep the car's tires spinning at a constant rate. If a tire loses traction, the car may slow down, but the engine and cruise control don't know that, and they don't tell the engine to rev up to make up any difference.

It could possibly happen if the cruise control were measuring the rotational speed of one of the tires which are not driven... not hooked to the transmission... but to do that sounds so wrong to me, as an engineering practice, that I can't imagine any auto company doing something that stupid.

It's a speed control device, and the speed being measured is nearly always computed from the rotational speed of some part of the car's power train, and an error signal is sent back to the throttle.

If a car aquaplanes, if it's front drive, the tires continue to spin at the same speed because the cruise control doesn't know anything about the tires' contact with the road or if they're sliding on water, snow, ice or whatever.

If the car is rear drive, the cruise control is controlling power to the back tires, and aquaplaning usually happens to the front tires, not the back, so while you might lose steering, the car still has no reason to accelerate.

Now, if you lose control of the front of the car and the back keeps on pushing, it could spin you off the road, but the engine still wouldn't be revving up because of it.

When Car and Driver or some other auto mag does a live test, I'll look into changing my mind, if they report what this story says.

Happy motoring!

But is there any truth to the last line: "NOTE: Some vehicles when the windshield wipers are on, you cannot set the cruise control." ?

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First rev: 02.02.2007; © Copyright 2007 by plusaf. All Rights Reserved