Just reading up on and trying to answer my own questions and came across this..
Tread pattern
One common misconception is that more tread equals more grip. That’s not necessarily the case.
While the tread pattern on a mountain bike or cyclo-cross tyre can have a big impact on grip, and the tread on car tyres helps to remove water in order to stop the vehicle aquaplaning, the shape and tiny contact patch of a road bike tyre means it ‘cuts’ through water. It’s too small for there to be a risk of aquaplaning.
While a tread pattern can help ‘squeeze’ grime away from the surface of the tyre, the most significant factor in determining grip is the rubber compound.
It is the compound, not the tread pattern, which largely dictates how much – or little – grip a tyre has, as well as its rolling resistance, durability and ride quality.
A softer, more supple compound will often be more prone to cuts, but it will conform with imperfections in the road and offer a bigger contact patch and more grip as a result. A harder compound, meanwhile, will be stiffer and less flexible, resulting in a ride quality which feels like the tyre is bouncing over the tarmac, rather than floating over it.
High-mileage tyres have traditionally been made from the latter as harder compounds have a lower wear rate, and therefore a longer lifespan, but the compromise can be less grip and a harsher ride.