When the road is wet, traction is low. If you ever slipped in the shower that concept should be pretty straight forward. But when the road is covered with water we can even find ourselves gliding (surfing if you will) on top. The idea (as you can see in the next clip) is that you can go fast enough that the water can carry your weight (you don’t have time to sink..).
The thing is that floating on water means that you can’t steer – no real friction on a liquid – and so you skid uncontrollably and because no friction, you don’t lose your speed as fast and so as long as the water are present you continue skidding…
So how come this doesn’t happen in every puddle? the groves on your tire are designed to allow water to drain through them while the majority of the tire is in contact with the ground. when the groves are too low (tread wear) / speed is too high / there are too much water / tire pressure too low – the water will form in front of the tire in a wave and the tire will “climb” over them. the next clip will elaborate on this.
And so the importance of checking the tire pressure is yet again obvious – along with making sure the tire tread is in good condition (the coin trick or professionally). You can see a good example of how surprising an aquaplaning accident could be.