Here's my tire routine: summer/warm weather I ride GP 4000s IIs. Reasonably durable, and a very nice ride. Good grip, low rolling resistance. I ride 700 x 25s. On October 1st through May 1st I ride GP 4 Seasons. Much more durable, and not a bad ride at all. They are at their best in cold or wet weather, and while they are not as supple as the 4000s tires, they're not bad. And I've never flatted one out, ever. I make the change over for one very simple reason: I really hate flats when riding in the cold or dark. I ride after dark during the late fall and winter months, and don't want to risk a flat under those conditions, a little slower tire doesn't bother me at all.