Tires?

I have Sumitomo 255/45/17's all the way around. They gripped GREAT when I first got them, almost a year ago. But the grip has decreased quite a bit, especially now that I've modded my car some. They still have good tread, they just don't grip as well. So while they don't last as long as some other tires, I got them for $120 a piece, and I doubt there's a lot of other tires that can match up to them for that.