[puddleglum]

Correct me if I'm wrong but I think the stock size is 155/80R13. The 165/50R15's are actually a 5.5% smaller diameter than stock. Since the question is posted by a fellow Albertan, I'm going to sidetrack a little. It's winter here for the next 6 months and the 12" winter tires don't fit. Forget changing brakes. Sell the 12's and the 15's. Buy a set of GOOD WINTER tires that fit. Traction trumps all until spring. There are a few winter tires that are LLR like the Nokian hakkapeliitta and have really good traction. It's a win win. Just don't go too big and heavy or you'll pay at the pump. As someone else who also drives in the city all the time, I think tire weight and LLR is abut 50/50. I haven't had a Firefly since I've been hypermiling but my Echo is in the same class. My winter tires are terribly inefficient but they have good traction and they came with the car. The summers are old and almost worn out. They're not LLR but they roll really well pumped up hard. They're 2.5% oversize but lighter because they're worn. In my opinion spend the money on good LLR winter tires and get some cheap summers. Try to keep the weight down and make some custom aero Ecomodder hubcaps to cover up the steelies. You can compare weights of tire and wheel combinations on the tire sites.