back on topic....
I learnt that I was right: wider tyres makes for more grip, fact.
I had a first gut feeling that F1 cars could not be that wrong to choose as wide a tyre as possible and here's the reason, translated into english from Italian, courtesy of an Italian member of the 350Z club, race engineer
I'll surely use wrong terminology in English, but hope you will still understand the goings on...
"there are 2 reasons why wider tyres produce more grip, due to the laws of physics :
1) from a physics point of view if you consider non-deformable objects, the resistance generated (= energy trasmitted by the tyre) is proportional only to the energy that lies on top of it, multiplied by the grip coefficient.
So if I increase the width area that touches the ground, the energy doesn't change. I simply have more surface, on which there is less specific energy (kg/ sq. cm) and I have no improvements to the " tangent strenght" (no idea on that term I'm afraid) transmitted. This is only valid for non deformable objects, though A tyre is NOT a non-deformable object and the wider is the contact area to the ground the less is the specific pressure for every sq. cm of tyre, and less is the deformation of the tyre. Deformation causes a loss of grip (adherence)
2) from a statistical point of view, not all tarmac has the same grip coefficient. With a wider tyre, you increase the chance of finding points on the tarmac that have a higher grip coefficient, and you reduce the risk of temporarily lose traction because say 30% of the tyre is touching a different type of tarmac. Consider that, once traction is lost, you go from a static friction coefficient (can't find the translation of this "moto di puro rotolamento" ) to a dynamic coefficient (again "moto di strisciamento") and the latter is always smaller than the former. In other words, if you break traction, you will have to take the foot off the gas to get back to the "puro rotolamento". Hence another reason why it's better to have wider tyres.
So, unless there is excessive air pressure in the tyres which penalises traction, wider tyres give more grip."
phew, that was hard