Minimum legal tyre tread depth

How much difference does tread make on a lorry?

On a dry road the main concern is getting the most rubber in contact with the ground so tread depth makes no difference until the tyre is completely bald, then grip is actually increased a tiny bit.

On a wet road it’s more complex because you need to avoid aquaplaning, that’s what the tread is for. Cars, especially modern ones with wide tyres, will easily aquaplane due to the low ground pressure and high speeds. By contrast a bicycle doesn’t need any tread as the high ground pressure (80-100psi) and low speed isn’t enough to lift the tyre off the ground. (OK, it’s not impossible, Schwalbe calculated that a slick would aquaplane at around 200Kph).

My guess is that the similar high ground pressure of a lorry tyre, combined with the restricted speed makes tread depth less important than for a car, although still more important than for a bike.

Anyone able to do the science bit?