Thread: Interesting but....

Urban myth. I read about this somewhere else a few months ago.

How can it accelerate when the tyres have lost contact ?

if anything it would be the reverse as tyres lose traction the engine would rev higher as its less under load, therefore causing the cruise control to slow the engine... thats my logical (or less than logical) thinking...

Steve

Actually, this is one of the few that has (some) truth to it...

http://www.hoax-slayer.com/cruise-control-warning.html

Certainly, using your vehicle's cruise control in wet or icy conditions can be dangerous - but not for the reasons outlined in this warning message. It almost goes without saying that aquaplaning can occur regardless of whether cruise control is engaged or not. Aquaplaning occurs when a tyre's grooves cannot remove water quickly enough and the tyre therefore loses contact with the road surface and skims across the top of the standing water. Car accidents often happen as a result of aquaplaning, but in many cases this is due to poorly maintained vehicles, driver inattention or poor road conditions and has nothing at all to do with cruise control.

That said, if cruise control is engaged when aquaplaning occurs, the driver's subsequent reaction could make the encounter worse than it may have otherwise been. For example, the driver may hit the brake heavily to disengage cruise control and this could lock up the wheels completely. Furthermore, drivers often move their feet away from the pedals when cruise control is engaged and they may also be a little less attentive than normal. In an aquaplaning situation the small delay caused by these factors could equate to the difference between a safe recovery and a serious accident. Also, an inattentive driver could hit the accelerator instead of the brake to disengage cruise control, and this could of course speed up the vehicle and lead to loss of control.

However, the claim in the message that cruise control itself can actually make the vehicle accelerate and fly through the air in a hydroplaning situation is dubious at best. A CarPoint Australia article that debunks the claims in the email notes:

This is the key that makes a nonsense of the email. Modern cars take their speedo reading from the driveshaft or transmission. This means the cruise control bases its responses on the speed of the driven wheels, not the car itself. This is an important distinction and fail safe position.

If the driven wheels skid because they lose grip, the spinning wheels will cause the speedo to show a higher reading which will force the cruise control to release the throttle faster than most drivers. Regardless of whether the car itself slows down or speeds up, the cruise control will always reduce the throttle no matter what until the driven wheels slow down back to the pre-set speed.

If the wheels continue to slip under this scenario, this will always leave the car travelling more slowly relative to the road, not faster as described in the email.

This finding is confirmed by the RAA's Technical Manager Mark Borlace, who explains:

"Should the car's tyres break traction with the road, such as in an aquaplane situation, the increase in wheel speed would be sensed and the cruise control system would then reduce the amount of throttle and maintain the set speed."

"Additionally, cruise control systems are deactivated as soon as the brake is applied. As braking is usually an automatic reaction in most emergency situations, the scenario of cruise control causing an increase in vehicle speed is highly unlikely."

Thus, there is no inherent factor in the cruise control mechanism itself that could lead to a hydroplaning vehicle speeding up and flying through the air.

http://www.truthorfiction.com/rumors...isecontrol.htm

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

Originally Posted by 5teve

if anything it would be the reverse as tyres lose traction the engine would rev higher as its less under load, therefore causing the cruise control to slow the engine... thats my logical (or less than logical) thinking...

Steve

I'll go with that

Got to agree that this is a myth.

when you loose grip with the surface (don't think I would want to drive on the pavement - but that's another thing) whether it's ice, rain, unless you brake the tyres will go faster - and if cruise is engaged, then it will sense higher speed wheels/prop/sensor - and will slow down.

..........and if you touch the brakes the cruise will disconnect anyway.

The sums just don't add up.

My 2c worth

I was driving a VT Commodoore ststaion wagon from Ayer Rock to Alice Springs.
It was well known at the time that this model tended to scrub the inner walls of the rear tyres and the company had replaced two sets of rear tyres while the front were still 70%.

We came over a rise and the rear left tyre blew. The car lurched and both back wheels lost traction for a split second. The cruise control was on and while the wheels were spinning the engine revved to buggery.
(I think the cruise control had detected the reduction in speed and was trying to accelerate teh car.)
The wheels made contact with the road again but with the increased revs from the engine it made the tail end lurch again (more violently than the first time) and again the wheels lost traction and again the cruise control tried to accelerate the vehicle.
This happened about four or five times and the car was fishtailing from the extreme left hard shoulder to the extreme right (thankfully there was absolutely no traffic on the road) I switched the cruise control off (tapped the brake) and performed the usual procedure for bringing a car with a blow out under control (slow braking and gearing down).....This may sound like I was composed and in control but let me tell you I was cra**ing myself at the time!!!)

I guess this gives creedence to the original story. When the vehicle speed reduces (such as when it starts aquaplaning) then the drive to the rear wheels is stepped up.
It might mean that the specific cruise control isn't using the gearbox speedo reader as its source of reference rather the speed of the front wheels?

It goes to show atht the more they pack into cars nowadays the less the driver has to do..and ultimately the less control the driver has

Jason

Originally Posted by Feral

I wonder how many people know about this?

A 36-year-old female had an accident several weeks ago and totalled her
car. A resident of Wollongong , NSW, she was travelling between Wollongong
and Sydney. 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 the policeman 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 policeman told her that if the cruise control is on and your car
begins to hydroplane -- when your tyres 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 policeman that was exactly what had occurred.
The policeman estimated her car was actually travelling through the air at
10 to 15 kms per hour faster than the speed set on the cruise control.
The policeman 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 road is dry.

The only person the accident victim found, who knew this (besides the
policeman), was a man who had had a similar accident, totalled 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.

I have received this email today. Would it be true and could it happen?


Discuss.

my mate the manager of the HSV driver training center in Yatala i think i am gonna have to go test that on there skid pan on the weekend will get back to ya
from kelvin

The increase in speed (alleged) may by due to less rolling resistance, in that water has less friction than a tar road.

I also dont think 'cruise' is smart enough to determine surfaces and would at least temporarily keep the drive wheels turning at the nominated road speed, so loss of friction would equate to wheelspin; cars with traction control would stop this happening; perhaps that's why tc goes with 'cruise' cars these days, and no-one has yet been any the wiser......


GQ