We were asked on the NRMA Facebook page about a chain email stating that cruise control in the slippery conditions, such as rain, leads to aquaplaning. This claim has been around for many years, however it may be more fiction than fact.
Tracing the origins of chain emails and viral posts can be almost impossible. Assessing any claims they may make, however, can be much easier. The below post landed on our Facebook page years ago, but the (mis)information is still circulated today:
"A 36-year-old female 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. 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. 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 15km/h 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."
While the message's closing sentence is good advice, the reasons given for arriving at this conclusion are misleading. Cruise control should not be used in wet conditions but there is no reasonable explanation why it would cause aquaplaning.
What is aquaplaning or hydroplaning?
Driving in wet conditions can be more hazardous than normal dry conditions as the wet conditions affect the tyre's ability to grip the road surface.
In order to maximise grip in these conditions, water is forced into a dispersed through grooves in the tyre known as 'tread'. At higher speeds, the tyre may fail to disperse water properly (especially if the treads have become shallower due to tyre wear), allowing the tyre to lift and ride atop a coating of water on the road. This is commonly referred to as aquaplaning or hydroplaning.
A tyre worn below its tread depth indicators are no longer considered safe for operation or capable of clearing the road of water, by both its manufacturer and any police officer that might pull you over.
How does cruise control operate?
Cruise control is a device used to keep the speed of the vehicle constant by monitoring wheel rotation and regulating the vehicle's engine output to suit.
Under a condition such as aquaplaning, where the driving wheels have broken traction (i.e. begun moving faster than the road they're on), the sensor would measure an increase in wheel speed. The cruise control system would then reduce the amount of throttle to maintain the set speed – the complete opposite of what is claimed to happen in the email.
In addition, cruise control systems are deactivated upon application of the brake pedal, which is usually deployed in emergency situations. Hence, cruise control causing a 15 km/h increase in vehicle speed during aquaplaning before driver intervention is highly unlikely.
Safe use of cruise control
The safest way to operate a vehicle is to ensure that, under all driving conditions, you can control the vehicle in a safe manner. As the system's 'cruise' control name implies, it is a device intended for use during steady driving situations.
Cruise control, when deployed, will attempt to keep the car at a constant speed set by the driver. If it has been set to 100 km/h speed, the car will enter a corner at 100 km/h. If a driver decides too late that this is an inappropriate speed for the corner, subsequent braking affect the balance of the vehicle which may cause instability. This will affect the vehicle handling and, if not correctly compensated for by the driver, can result in a loss of control.
Wet roads significantly affect the grip of the tyres, and this can make corrective actions by the driver much more difficult to judge. Accordingly, the driver should assess the conditions of the road and adjust vehicle speed so it is suitable for the road.
To better understand safe operation of its cruise control, you should refer to your vehicle manual. Many owner's manuals suggest cruise control should not be used in heavy traffic driving, city driving, and winding, undulating, slippery or unsealed roads.
The takeaway message
The chain email's closing message is true, but it's the only part that is. Drivers should avoid using cruise control in slippery and/or low visibility conditions in general, but your car isn't going to grow wings and become airborne if it hits a puddle and momentarily aquaplanes.
