Just thought I'd give an update on the iridium TTs. As I've mentioned before I did notice the car is less prone to downshifting under heavy load ie hills. One thing I've also noticed is that despite being cold weather and cars arguably using more fuel my mpg has improved. I use to get an average of around 31-32 mpg. My avg calculated mpg now has improved to 35.6 mpg despite being winter, going mostly on short drives and paying no attention to driving with a light foot. I have accrued so far a total of about 4000miles on them.