Tire pressure makes a big difference. I'm assuming you pump them up to 35 psi (or more) for the highway miles? I kept mine fully inflated when I drove around town.
I used to worry about pressures and air my ET street Pros up for the street and down for the track. Then I realized they drive as well at 18psi as they did at 30. I just leave them at 18 and have never had any issues. I swap them out for new about every 2 years anyway. Since I quit spinning them on the street, they have worn much better.
