Red5 : I run the same tires front rear, 40 Fast Tires. I run a softer front spring then i do in the rear. That might be the reason you see a difference and I don't. Tires wear pretty darn even. I have run at tracks were you run 4 quals and a 30 min main and lose less then 2 mill over the entire weekend. Including practice. Start with 61 mm tires and still 59 or better at end of weekend. This happened once. But I was like this is cool. But most of the time its not a sig. diff.