tsl

Where many people go off the rails regarding tires is the knobby (or aggressive tread) vs. studs issue. They seem to think if you have one you don't need the other.

This is a false assumption.

Aggressive tread (or knobbies) grip loose surfaces, like snow, mud or sand. On ice, they're just as useless as slicks.

Studs bite into ice. Newbies think that's useful mainly to starting and stopping. But as it turns out, it's mainly useful for steering and balance, so the bike doesn't slide out sideways from beneath you. This is also why, if you can afford only one studded tire, it goes on the front. When the front wheel slides out, it goes fast and you go down quick and hard. When the rear slides out, it does so slowly and you can sometimes get a foot out in time.

Since studs are so small, they don't do much for grip in loose surfaces. So you need both in a winter tire--aggressive tread and studs.

As for longevity, it depends entirely on the type of stud. Plain steel studs, found in cheap tires (like Innova) won't even last one season when ridden daily on roads. There's a reason why they sell those restudding kits and no-one else does. Carbide studs, found in more expensive tires (like Nokian, Schwalbe and Continental) will last several seasons. I have five seasons on my Nokians with no appreciable wear.