Another wet tyre question

[gcrossan]

Hi,

The TV commentators kept making a point in their coverage of the British GP that the wet tyres "clear 60 litres of water per second".

I'm guessing this figure is calculated simply by tyre footprint x tread depth. Tyre footprint will remain the same but the tyre is rotating so a new series of 'empty' grooves come into play and are constantly contributing to this clearance of water?

Is the above correct?

So, at what speed is this '60 litre' figure reached? At 200mph, which the car is capable of, but is unrealistic (impossible?) in those wet conditions, or an average speed of what we would expect to see over a wet race distance? Is it just some clever tyre manufacturer stat or is this a realistic figure of how much water each corner of the car is shifting?

Cheers

[Diff-user]

from what i have gathered, the tyres clear up that much water at 300 Kmph or so. The quantity being a linear function of tyre speed. and cars DO go almost just as fast in long straights (aquaplaning is less of a threat at very high speeds because of the high downforce in these), its indeed the slow and medium speed corners and the braking zones that often get the better of these cars. In the end though, its just a stat that tyre manufacturers have been doling out sans the catch that the amount is speed sensitive for many years now

[peanutaxis]

Hi,

The TV commentators....

This is another comment by tv commentators that annoys me. The amount of water that can be cleared per second is meaningless. What matters is how much water a tire can clear per revolution, or even better, how much water a tire can clear per area (all this translates to is how much water on a unit area of tarmac can a tire deal with).

For instance, a tire might clear 10 litres of water per meter squared. That one basic number then tells you that a tire can clear 10 litres of water every time it covers one metre squared of tarmac. Or in other words: if there is more than 10 litres of water per every one meter squared of tarmac, that tire cannot clear that amount of water.
I think you are right that they just multiply through and work out how much they can clear when the car is traveling at max speed. That number is probably then quoted by Pirelli because it sounds big and the commentators jump on it, but it's pretty meaningless, especially to an engineer, and very especially to a Pirelli engineer!

Conceivably a car could travel so insanely fast that the water being pushed aside by a tread block would not have enough time to reach a channel in the tire and the tire would start to aquaplane. But clearly this is not an issue - or rather, if it was they would simply design the tire with smaller tread blocks so that the water DID have enough time to reach a channel.

Another aspect is the tread depth. As the tire wears it can clear less and less water.


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