Nobody forced Nokian to market their tires as AS so they used to have decent summer tire now they have mediocre all season (because winter traction sucks and wet breaking is not that good).
Oh well.
Krzys
When going by tread depth difference one makes assumption that tires have the same circumference to start with.
It may or may not be the truth.
It is safer to take a tape and measure circumference.
Krzys