Motorway aquaplaning - an avoidable accident?

[samoht]

This discussion arose from ATM kindly sharing his rather nice 996 CSR and his car history on Reader's Cars.

As part of that, he mentioned he'd suffered a couple of cases of aquaplaning on motorways

ATM said:

In the long and distant past my first Porsche was a 986 Boxster gen 2 facelift.... In the first 2 or 3 weeks of buying it I aquaplaned on the motorway and destroyed the car.

ATM said:

My next Porsche was a 2012 981 Boxster S with PDK gearbox.... I had another Aquaplaning incident.



Yes I destroyed another Boxster by Aquaplaning but this time I knew the car was properly aligned and I had good matching tyres.

This lead to a discussion of aquaplaning, which I've moved here to allow further discussion without derailing the OP's thread

ATM said:

Bright Halo said:

TheJimi said:

As for the aquaplaning - are Boxsters particularly susceptible? (and I'm not being facetious either - I genuinely don't know!)

I don’t think so.
Mine is on semi slicks and I haven’t had a problem (so far)

Generally front engined cars less prone due to weight over the front wheels. These should cut through the standing water and leave a channel for the rears to use.

Light weight
Fat Tyres
Speed
Tread depth
Tire design for getting through water

The above are your enemies when it comes to standing water. So generally I would say all Porsche sports cars are more risky than your average city car due to their lowish weight, fat tyres and less weight over the front.

I have never aquaplaned in any other cars. Little video showing what can happen. The car just goes light, rotates, then grips and spits you off in whatever direction it is pointing.

I dont want to say I a a brilliant driver. But you would need to be seriously good to catch this and save it.

DuncanM said:

Sorry OP, but writing off two cars, in the exact same way, and not acknowledging that your driving needs to change in the conditions that both incidents occurred?

Skinnier tyres won't help you, driving to the conditions will.

ATM said:

You're absolutely right. I do blame myself. But even driving to the conditions with skinny tyres will be safer than fat tyres. Surely we can agree to that?

DuncanM said:

I guess so to a point, but for me, driving fast in those conditions, in a sports car = recipe for disaster.

Best just to pootle around and get home safely when it's that wet - both incidents must have been scary?

I hate motorways for fast driving, dangerous places at the best of times + unmarked cars etc.

ATM said:

I wasn't speeding. I can say this for definite.

But even at 70 [not sure if I was actually doing 70 because of poor visibility] you can still spin off in a light sports car with fat tyres.

DuncanM said:

Both crashes would be due to acceleration - asking the rear wheels to go faster than the front. You will hopefully know this though.

You own and have owned some serious metal, and they need a delicate right foot in the sopping wet.

Slippydiff said:

You don’t need to be accelerating to aquaplane ... Sure if you’ve got the accelerator nailed it’ll exacerbate the problem, but you can aquaplane at 80mph on the lightest of throttles (or indeed no throttle at all) on a motorway with 8mm of surface water, when you’ve got 7mm of tyre tread. That’s not to suggest that lack of tread depth is always a major factor, as if there’s sufficient surface water and the tyre is incapable of moving it despite having plenty of tread, the car will still aquaplane.

samoht said:

Evo Tyre test said:

In a straight line we measured the maximum speed each tyre attained in 7mm of water before it overspeeded by 15 per cent.

1. Dunlop Sport Maxx ... 45.5 mph

7mm isn't a very deep puddle, and 45mph isn't very fast - pootling speed, I'd say. This was the best-performing available brand-new premium tyre, on a nose-heavy Audi.

The belief that anyone who encounters aquaplaning must have had bald tyres or been driving badly is not only unfair on the OP, but it's also a dangerous misconception.

DuncanM said:

This is dangerous rubbish, anyone blaming these crashes on anything other than not driving to the conditions is enabling poor driving, and will learn absolutely nothing.

I'm astounded tbh, it'd be nice if someone else would like to chime in on this? I didn't want to derail the thread, but this is utterly nuts?

Stegel said:

I’ve experienced aquaplaning in a months old, <5k mile (stated re tyre wear) E class estate - as far from the OP’s car as you can get. 75mph on cruise control on M74. Brilliant sunshine after heavy rain. The front end stepped out dramatically, but fortunately the car’s systems, and it finding dry tarmac, sorted it all out before I really knew what was happening, even so I was in a different lane by then.

Not a driving God, but I’d certainly say my driving was appropriate to the conditions. It’s in the “sh#t happens” category in my view, and bumbling along at 40mph in the same conditions would be far more dangerous.

Bright Halo said:

I believe you can theoretically experience aquaplaning above 45mph.
However there are many factors. Speed, tyre pressure, tyre size, depth of tread, depth of standing water etc.
There is a complicated equation that calculates aquaplaning speed but even this is flawed.
The real risk factors where possibility of losing traction grows exponentially are the combination of Tyre tread depth below 3mm, speed above 65mph and standing water greater than 10mm.
Vehicle weight not so much a factor although does play its part.
Lowering tyre pressures is a bad idea when surface water is present as the tyre can be more concave in the centre and prevent water from being pushed away.

I think a mod should move the aquaplaning posts away to form a separate discussion so we don’t clutter up this thread.

Slippydiff said:

DuncanM said:

Both crashes would be due to acceleration - asking the rear wheels to go faster than the front. You will hopefully know this though.

You own and have owned some serious metal, and they need a delicate right foot in the sopping wet.

It would appear your understanding of what aquaplaning is, and what causes it, maybe somewhat lacking.

Firstly it has nothing to do with the speed differential between the front and rear wheels, and as I and Samoht have said, you don’t need to have the throttled pinned heavily to experience aquaplaning, because aquaplaning occurs when the depth of surface water on the road is such that the tyre driving through it, is incapable of clearing sufficient water to enable the tyre to remain in contact with the road.
When this happens the tyre will effectively be raised up by the bow wave formed in front of it, and onto the plane” ie it will be riding on the surface of the standing water.
At this point you’ll experience the horrible feeling the OP felt, that being the steering going extremely light (as if driving on ice) the car feeling unstable, and if you were to lift off/brake, you’d find the brakes ineffective, and the car would most likely start to rotate, by the time most drivers have established what’s going on, it’s too late and the car will more than likely have sufficient momentum that the ensuing spin will be all but uncatchable in the space available.
As Samoht and I have stated, this can happen at as little as 45mph, or on the motorway/autobahn at much higher speeds.

All too often the driver won’t even see the heavy surface water at all, or until it’s too late.

Whilst I agree one should drive to the weather conditions, all too often aquaplaning can occur because of poorly drained/designed roads or blocked drains and gulleys.

DuncanM said:

Oh how strange, I honestly thought people would chime in on my side

I still believe acceleration would make the crashes much more likely, I didn't state that acceleration causes aquaplaning in my post, but was trying to nudge the OP towards looking at his driving.

Cars are inanimate objects.

Single vehicle accidents are (typically) the fault of the driver.

Having two exact same crashes should make you question your driving, and not hunt for skinnier tyres as a solution.

Blaming xyz instead of driving inappropriately for the conditions is a concerning mindset, I'd hate for the OP, or anyone else to be hurt due to not changing said mindset.

So.. in the case of driving down a sopping wet motorway, assuming tyres with a reasonably deep tread, how much would you slow down? And would you be confident that would be slow enough to avoid the risk of aquaplaning?

[samoht]

DuncanM said:

Oh how strange, I honestly thought people would chime in on my side

I still believe acceleration would make the crashes much more likely, I didn't state that acceleration causes aquaplaning in my post, but was trying to nudge the OP towards looking at his driving.

Cars are inanimate objects.

Single vehicle accidents are (typically) the fault of the driver.

Having two exact same crashes should make you question your driving, and not hunt for skinnier tyres as a solution.

Blaming xyz instead of driving inappropriately for the conditions is a concerning mindset, I'd hate for the OP, or anyone else to be hurt due to not changing said mindset.

As a general rule I agree with your last statement. Any time one has an accident, or narrowly avoids one, one should always be asking 'what could I have done differently to avoid that situation?'.

I do however believe that some cases of aquaplaning are an exception to this general rule.

The reason is that in scientific tests like the evo tyre test I posted above, using brand new premium tyres, they were aquaplaning at 45mph in 7mm of water.

So I suppose the question is, given a situation where you're on a motorway in or after heavy rain, and you're aware of a risk of aquaplaning, how do you judge how many mm of water are on the road, and how do you judge how slowly you need to go with your vehicle and tyres to avoid the risk of losing touch with the tarmac?

[samoht]

All incidents of aquaplaning could be avoided by driving more slowly.

Many (most?) aquaplaning incidents could reasonably be avoided by driving more slowly.

However, it's not IMHO reasonable or safer to be doing 35mph on a motorway any time it's wet, or emergency braking if you see what might look like standing water ahead, so there's always a remaining risk that you might encounter an unexpected puddle that is deeper than the critical depth for your vehicle tyres at the speed you're doing, and aquaplane.

Therefore personally if someone reports aquaplaning, I don't necessarily assume that they were driving poorly or even that they could necessarily reasonably have avoided it. It's certainly a possibility that they were driving inadvisably, but IMO not definite.

[samoht]

C.A.R. said:

I'd like to 'wade' in with an opinion on the original argument that skinnier tyres are better...

I drive a hybrid company car daily (it's horrible) which has eco tyres on @ 195 section, so "skinny" by todays' standards, especially compared to a sports car.

If you hit standing water in that thing you'll still aquaplane like buggery. Aquaplaning is surely just a point at which the tyre can't disperse enough of the water beneath it quickly enough, so it sails above it? Skinny eco tyres do not help mitigate that danger.

A wider tyre has to disperse more water per metre travelled, so all things being equal it'll start aquaplaning at a lower speed. So narrower tyres will resist aquaplaning better, all things being equal.

What you're probably encountering is that the eco tyres are designed to minimise rolling resistance, so probably with fewer lateral grooves. This means the better economy is achieved at the cost of aquaplaning resistance. If you had those eco tyres in a wider size, it would be even worse.

Between two tyres with the same tread pattern of different widths, the narrower one resists aquaplaning better.

You can see the aquaplaning section in this test, they had identical Goodyear Eagle tyres in 225, 255 and 285 widths and tested them on the same car. In the aquaplaning section, the 255 scored 5% slower than the 225, with the fat 285s being 13% worse.

[samoht]

Some of the above responses feel to be going over the same ground again, so by way of a summary, here's what I personally think I've learned from our discussions:

• All aquaplaning incidents are avoidable by driving more slowly
• It's entirely possible to experience aquaplaning within the speed limit
• In most cases there is sufficient warning of a risk of standing water for the prudent driver to reduce speed sufficiently, but not always
• In the worst conditions it may be best to pull off a motorway and wait for the rain to relent

• Tyre choice and tread depth are significant factors
• Vehicle-specific factors such as weight, weight distribution and tyre width also affect the critical speed for aquaplaning
• Therefore just because the cars in front pass through an area of standing water safely, does not mean that you will
• Specifically, performance cars with light weight and wide tyres, which have superior roadholding in the dry, are at greater risk of losing control through aquaplaning in the wet.

• The best response to aquaplaning is to keep the controls neutral until grip returns, otherwise you increase the chance of losing control when some or all tyres abruptly regain grip