Aquaplaning and Cruise Control

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Mon 25 Mar 2013 18:03
Aquaplaning and Cruise Control - hillman

I've received a .pdf regarding the dangers of using cruise control while driving in the rain. It seems to make very good sense.

A. Has the subject been brought up recently ?

B. What is the formula relating wheel size to the speed of on-set of aquaplaning ?

I've experienced the feeling of loss of control at approx 60 mph on the M62 despite having good tyres.

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Mon 25 Mar 2013 18:09
Aquaplaning and Cruise Control - Bobbin Threadbare

I've received a .pdf regarding the dangers of using cruise control while driving in the rain. It seems to make very good sense.

A. Has the subject been brought up recently ?

B. What is the formula relating wheel size to the speed of on-set of aquaplaning ?

I've experienced the feeling of loss of control at approx 60 mph on the M62 despite having good tyres.

B. aquaplaning speed in mpg = 10.27 x sqrt (P) where P is tyre pressure

I have done this at about 35mph. Not nice at all!!

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Mon 25 Mar 2013 18:22
Aquaplaning and Cruise Control - Armitage Shanks {p}

This more common formula was used when I was interested in these matters in connection with aquaplaning aircraft tyres; it is 9 x Sq Rt of tyre pressure. It is easier to calculate and gives a slightly lower speed which may be helpful!

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Mon 25 Mar 2013 18:28
Aquaplaning and Cruise Control - RT

Tyre pressure in psi or bar ?

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Mon 25 Mar 2013 18:47
Aquaplaning and Cruise Control - Bobbin Threadbare

Haha I have typed mpg when I meant mph. The 9 x sqrt pressure comes out in knots, not mph. Pressure in PSI.

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Mon 25 Mar 2013 18:48
Aquaplaning and Cruise Control - Armitage Shanks {p}

Sorry - PSi. TP 36 = Aquaplane at or above 54mph

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Mon 25 Mar 2013 19:12
Aquaplaning and Cruise Control - MikeTorque

There is no exact formula as such for aquaplaning as there are many factors that need to be taken into consider, a wide tyre width is one of the most significant factors.

There is however the formula V = 8.6 x √P which is based upon the validation of hydrodynamic lift theory by experimental evidence.

Examples :
30 psi tyres would equate to 47.1 mph.
40 psi tyres would equate to 54.4 mph.

In addition there are several types of aquaplaning as the science gets more complicated.

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Mon 25 Mar 2013 19:31
Aquaplaning and Cruise Control - RT

Doesn't the tyre tread pattern and depth play a major part?

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Mon 25 Mar 2013 19:38
Aquaplaning and Cruise Control - leaseman

I think that it's most likely to be the I.Q. of the driver that has most weighting to whatever formula is used!

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Mon 25 Mar 2013 19:45
Aquaplaning and Cruise Control - hillman

"Doesn't the tyre tread pattern and depth play a major part?"

RT - I'm sure that the tyre manufacturers would comment strongly on this point, but I don't think that it materially affects aquaplaning. Once that wedge of water has built up it's almost impossible to dissipate except by slowing down.

leaseman - "I think that it's most likely to be the I.Q. of the driver that has most weighting to whatever formula is used!" You're quite right !

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Mon 25 Mar 2013 20:03
Aquaplaning and Cruise Control - Bobbin Threadbare

There are several journal papers which present results of investigation into tyre tread pattern and aquaplaning. Certain patterns are found to be better than others i.e. the aquaplaning speed is higher for certain tread patterns. The tread pattern and depth strongly affect the aquaplaning characteristics eg trb.metapress.com/content/n47gp727v2v4614k/?genre=...0


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Mon 25 Mar 2013 20:12
Aquaplaning and Cruise Control - RT

"Doesn't the tyre tread pattern and depth play a major part?"

RT - I'm sure that the tyre manufacturers would comment strongly on this point, but I don't think that it materially affects aquaplaning. Once that wedge of water has built up it's almost impossible to dissipate except by slowing down.

So a slick, or illegally worn tyre will aquaplane at the same speed as a nearly new tyre ?

Edited by RT on 25/03/2013 at 20:13

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Mon 25 Mar 2013 20:19
Aquaplaning and Cruise Control - Armitage Shanks {p}

I further recall that, once a tyre is aquaplaning, whether it has tread or not, it will not stop doing so when one slows down to below the speed it started at. One has to get well below it and bearing in mind one or more wheels is not in contact with the road, steering and braking are not available this can be tricky.

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Mon 25 Mar 2013 20:49
Aquaplaning and Cruise Control - unthrottled

formula V = 8.6 x √P which is based upon the validation of hydrodynamic lift theory by experimental evidence.

Examples :
30 psi tyres would equate to 47.1 mph.
40 psi tyres would equate to 54.4 mph.

Aquaplaning is is the same phenonemon as hydrodynamic lubrication. The condition for hydrodynamic lubrication is found on a Stribeck diagram and is given by Mu*N/P >a constant

where P is the contact pressure, not the internal air pressure of the tyre, Mu is the viscosity of the fluid (which depends on the temperature), and N is the rotational speed.

In the same way that the pressure of the oil film in the main bearings of the crankshaft is hundreds of times higher (and not dependant upon) the pressure of the supply from the oil pump!

Any formula that is further simplified is merely an empirical correlation for a particular scenario and lacks any generality whatsoever.

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Mon 25 Mar 2013 21:28
Aquaplaning and Cruise Control - MikeTorque

The formula I quoted stands. It's often used by pilots to quickly calculate takeoff and landing performance and Dynamic Hydroplaning.

The formula V = 8.6 x √P uses psi inside the tyre.

The formula you quoted for hydrodynamic lubrication is more suitable for the contacting surfaces of bearings.

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Mon 25 Mar 2013 21:50
Aquaplaning and Cruise Control - unthrottled

The formula V = 8.6 x √P uses psi inside the tyre.

As P tends to 0, the formula predicts that the velocity for the onset of hydroplaning also tends to 0. So a deflated run-flat tyre with no air pressure will aquaplane whilst stationary!

Conversely, a grossly over-inflated tyre could run at the speed of light without hydroplaning.

The formula is also independant of vehicular weight-again at variance with reality. A heavily laden vehicle has a higher velocity for onset of hydroplaning than a lightly laden one.

The formula takes no account of the width of the tyre-again at variance with reality.

The formula I quoted stands

it may be a useful empirical correlation for planes. For cars, no. Planes have wings and hence lift which varies with velocity. This changes the relationship entirely.

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Wed 27 Mar 2013 11:29
Aquaplaning and Cruise Control - hillman

Down to practical things, I don't really understand how the system works. Can anyone spell it out for me ?

Thinking about it, If the cruise control operates on the driving wheels, logically, the effects should be different for front wheel and rear wheel drive cars.
A. If the car is front wheel drive and traction is lost because of the wedge of water, then the cruise control will try to maintain the speed by turning the wheels at the original rate. The car will start to slow down because traction is lost and then grab disconcertingly when the wedge dissipates and traction resumes.
B. If the car is rear wheel drive then the front wheels may begin idling - the cruise control might think that the car is slowing down and increase speed accordingly.

It's very unlikely that the cruise control would do anything to make the car 'fly' but the .pdf didn't say anything about the road layout. After the driver lost control did the car leave the road, go over the kerb etc ? It's relatively easy to make a car fly through the air if you are going fast enough and you meet a bump - happens all the time, so to speak.

http://www.telegraph.co.uk/motoring/news/9950976/Audi-TT-takes-off-and-crashes-into-house.html

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Wed 27 Mar 2013 11:43
Aquaplaning and Cruise Control - skidpan

http://www.telegraph.co.uk/motoring/news/9950976/Audi-TT-takes-off-and-crashes-into-house.html

What has that link got to do with cruise control and aquaplaning.

The Audi TT was clearly speeding and being driven by a total idiot.

With regards to cruise control we only use it on our car when traffic conditions allow and when road conditions are suitable. There have been several occations in the past when I have not used cruise control on a virtually empty road because road conditions in my opinion required total concentration and control even when driving at sensible speeds.

As always it comes down to common sense which unfortunately is a commodity that is not supplied to a large percentage of the population these days.

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Wed 27 Mar 2013 17:16
Aquaplaning and Cruise Control - hillman

"What has that link got to do with cruise control and aquaplaning."

I included the link to show that if one is careless one can jump the car a considerable distance. One of my work-mates once lost control on a hill road and jumped the car up the banking, over a stone wall into a field without obvious damage to the car. He drove around the field until he came to a padlocked gate opposite a farmhouse. He knocked on the door and when it opened a shocked woman told him that he couldn't park the car in the field. It took a little diplomacy to persuade her to get the key to the padlock.

One of the reasons I don't use cruise control is that my car is very relaxing to drive and I need stimulus.

Anyhow : How does the cruise control work on front wheel and rear wheel drive cars ?

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Thu 28 Mar 2013 07:39
Aquaplaning and Cruise Control - skidpan

Anyhow : How does the cruise control work on front wheel and rear wheel drive cars ?

Well on our car you get to the speed you want to cruise at you press a button on the steering wheel and it maintains that speed. Its sorted magically by the car.

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Wed 27 Mar 2013 18:20
Aquaplaning and Cruise Control - Andrew-T

P is the contact pressure, not the internal air pressure of the tyre, Mu is the viscosity of the fluid (which depends on the temperature), and N is the rotational speed.

As aquaplaning results when the water between the tyre and the road cannot be squirted out fast enough, temperature must have a significant effect, as the viscosity of water is quite strongly temp-dependent, like most liquids. It follows that aquaplaning will happen at a lower speed in near-freezing temps. than in a summer thunderstorm (other things being equal).

Edited by Andrew-T on 27/03/2013 at 18:24

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Wed 27 Mar 2013 18:53
Aquaplaning and Cruise Control - dadbif
Interesting thread, in summary, when it is p***ing down, slow down if your steering feels light.
QED
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Wed 27 Mar 2013 19:54
Aquaplaning and Cruise Control - MikeTorque

Yes indeed, or better still earlier.

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