Just a word of caution - I replaced the wheels and tires on my 03 Civic Hybrid about a year ago. I was very careful to get LRR tires (Continental ContiTouringContact CV95, which are GREAT), and I even dropped 2.3 lbs per wheel using light-weight rims (Kosei). I still lost an overall 2 MPG. Maybe the TCH isn't as touchy, but I think spoked wheels and sticky tires will have an impact.

*** Retired after 65,000 outstanding miles ***