Aquaplaning - what it is and how to deal with it

With so much rain around (Winter 00/01), standing water on the roads has become common, and many riders fear aquaplaning.

So what is it, how do you recognise it's happening and what do you do about it?

What is it?

When the water is sufficiently deep or speed sufficiently high, the water that the tyre attempts to displace to the sides cannot get out of the way fast enough and builds up as a wave just in front of the tyre. Aquaplaning occurs when the tyre rides up and "floats" on that wave, losing contact with the road surface. Consequently you have no grip! It normally affects just the front wheel, as the rear follows in the trough cut by the front tyre. It's near enough the same principle that the Seacats across the Channel and the Irish Sea work on.

Fortunately for bikers, it's actually pretty rare because even a wide sportsbike tyre is U or V-shaped with a relatively long, thin contact patch that cuts through the water like a ship's bow. You seem need to hit standing water over several metres for the tyre to climb up on that wave. It's happened to me just twice in 25 years, once on the side a hill near Bastogne in Belgium, where a fast wide road climbs down out of the Ardennes, and once closer to home in West Kingsdown, just up the road from Brands Hatch, where the road is wide and flat.

By contrast it's actually much more likely to happen when you are driving a car because from the front the car tyre presents a flat, broad profile with a short wide contact patch. I've probably aquaplaned a dozen times this winter on the motorways on four wheels.

Where is it likely to occur?

Let's face it, if you see a big puddle, you slow down on the approach, and either avoid it or ride through cautiously. Even if you don't see a deep puddle for some reason, the resistance of hitting it slows the bike down pretty rapidly and loads the front tyre just like braking, increasing the pressure on the tyre to push the water out from under. The resulting shock might do nasty things to the steering (like try to wrench it from your grip), but this is not aquaplaning (at least, not for more than a few fractions of a second).

The danger time is when the road surface is just awash with standing water a few millimetres deep but for a considerable distance. The sort of depth where if it were a small puddle you wouldn't normally think twice about riding through it at speed. So you don't slow down and you hit the water at speed. You are now at prime risk of aquaplaning as the front tyre rides up on that bow wave.

How do you recognise it?

The bike carries on in a straight line, with no real sense of slowing down, but the bars go light and floaty. In extreme circumstances they can even move from side to side as you continue in a straight line. It's a bit like riding on ice, but with one important difference - the rear wheel usually continues to drive - on ice, your first warning is often wheelspin.

What do you do about it?

Watch out for shallow sheets of water, perhaps after a thunderstorm or prolonged heavy rain. Look out for places where run-off from a field or an overflowing drain, or other standing water is covering the road.

Like all riding, your best defence is thinking ahead and anticipating. First watch out for places it might happen. Wide carriageways are worst, particularly motorways and dual carriageways. Whereas two lane roads like A roads and country lanes normally have a crown that drains water to either side (but see exception below), the surface across each carriageway is usually nearly flat, which can lead to large areas of shallow standing water. Where the surface has sagged beneath the weight of lorries, you often get standing water in the wheel tracks - keep out by riding in the centre of the lane, and use the outside two lanes for preference. This type of road also means you are likely to hit the water at considerable speed, and with all the spray around you may well not see the problem until the last second. So try to keep a good gap, and don't go excessively quickly.

The other place it can happen is where the road surface is superelevated (that means the entire road slopes to one side so the road is banked like the stands at a football ground - normally found on new bypasses and newly rebuilt A roads). This eliminates the problem of adverse camber, but where water is running onto the road (perhaps an overflowing drain or a driveway) rather then forming a big puddle at the side of the road, it will flow down the slope from the higher side, spreading out in a sheet, to the lower side. It's not uncommon to watch the flow go from side to side across the road several times as the road changes direction

So what do you do when you see it? Slow down. If you see it too late to reduce speed, the answer is, as always in these situations, try to relax, grip the tank with your knees and do nothing harsh or sudden. The wiggling steering is not really a problem - when the front tyre bites again, if it is at a slight angle loose elbows will let the bike sort itself out - hanging on to the bars for dear life always make things worse. Your grip on the tank will ensure you stay in place during any ensuing wobbles.

Roll gently off the throttle and the front wheel should quickly regain grip. Applying the front brake could cause it to lock. You might be able to apply the rear but again, do it gently. Don't try to steer - you won't be able to.

Let the bike do its own thing and in a second or two, you should be out the other side.