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Aquaplaning - what it is and how to deal with it
When I originally wrote this tip almost twenty years ago, my main worry was winter weather. But in the last few years, torrential rain and standing water on summer roads has become just as common and it can be a real hazard. I don't mean just ploughing into standing water and having the bike stop almost dead, or even finding that the puddle is actually a pothole, but the problem of aquaplaning. So this article explains "what is aquaplaning, how likely is it to happen, how do we recognise it's happening and what do we do about it?"
Let's start by explaining what aquaplaning is. I think the term has probably been borrowed from ship design. A ship has to push water aside in front of it, and when that vessel's speed is sufficiently high, the water cannot get out of the way fast enough. So the vessel tends to rises up and ulimately 'rides' on the wave it's created. That's the basic principle behind high speed ferries.
Tyres do pretty much the same. When water is sufficiently deep and speed sufficiently high, the tyre cannot displace the water to the side quickly enough. A wave builds up ahead of the tyre's contact patch and with just a bit more speed and the tyre rides up and 'floats' on its own bow wave. And that means it's lost contact with the road surface, and the tyre has no braking or steering grip!
Here's the good news. Whilst aquaplaning is quite common when driving a car - the barrel-shaped profile of a car tyre has a broad contact patch that pushes water ahead of it - a motorcycle tyre is U or V-shaped and the relatively long, thin contact patch cuts more effectively through standing water, much like a ship's bow.
In my experience, aquaplaning is pretty rare on two wheels compared with four. In fact, if we do much motorway driving in wet weather, aquaplaning is quite common. But I can count the times it's happened on a bike on one hand.
The danger seems to be a road surface just awash with standing water, where we we wouldn't normally think twice about riding through it at a modest speed. It happened once near Brands Hatch, where the road is wide and flat - it's an old concrete surface underneath the tarmac skim and so there's no camber to clear the water, so there was standing water over a considerable length of road. The speed limit is only 40, so it seems that it's the distance the standing water stretches that matters, rather than flat-out speed. I had a similar incident in the Ardennes in Belgium on a brand-new road that was 'super-elevated' - that is, cambered so that the entire road 'banks' for each corner. This seemed to trap the rain from a thunderstorm so that rather than flowing OFF the surface, it acted more like a channel of the water.
Hitting a short stretch of deep water doesn't seem to create the right circumstances for aquaplaning. I suspect this is because the resistance of the water creates a sudden deceleration so there's no chance for that wave to build. The impact will try to wrench the steering out of our grip, but it's not aquaplaning. And, let's face it, if we see a big puddle, it'd be a good idea to avoid it when possible, or slow down when we can't as we've no idea what's under it.
So watch out for shallow sheets of water, particularly after a thunderstorm or prolonged heavy rain. Look out for places where run-off from a field or an overflowing drain flows into the road. Motorways and dual carriageways are bad because two lane roads like A roads and country lanes normally have a crown that drains water to either side, but the carriageways on a dual carriageway are usually flat, Watch out too for standing water in truck wheel tracks. At speed, and with spray flying around, we may well not see the problem until the last second. So try to keep a good gap, and don't go excessively quickly.
In my experience, the warning sign that the bike is aquaplaning is that it keeps going in a straight line, but the bars go light and floaty-feeling. They may even move from side to side. It's a bit like riding on ice, but with one important difference - on ice, the first warning is often wheelspin but when aquaplaning, the rear wheel continues to drive the bike forward, presumably because the rear is often following in the trough cut by the front tyre. It's front tyre grip that's compromised.
If we suspect we might be aquaplaning, the best answer seems to be, as is often the case, to keep a relaxed grip on the bars - hanging on for dear life always makes things worse. Lock onto the tank with the knees to keep the weight off the bars and do nothing harsh or sudden. Once again, in my experience, if we simply roll off the throttle gently, the reduction in speed plus the extra loading at the front gets the front tyre to cut back down through the water to regain grip. But don't apply the front brake - if it's floating, it could lock. If it's necessary to brake, use the rear gently. Don't try to steer until there's feedback through the bars telling you that the front tyre is back in contact with the road surface.
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