Hi, Mia Culpa! It was remiss of me not to make clear my Saab/Studded Tyres position correctly? I was of course referring to their rallying use, so unless used on UK roads they would legal in the sport. Saab used the narrow section tyres in non-studded form to good advantage
When a rally car gets on to public roads they must comply with all traffic regulations.
As for pressure or force? The weight of the vehicle surely imposes downward pressure, so facilitates more forward movement when the wheels rotate.
Don't shoot me, I'm only a spanner turner, not a design engineer.
* I've heard of tricycle riders, pedal powered, who use studded tyres? Wouldn't want to make contact between rump & tyre