Tires: tires switch for better gas milage, 18 inch rims, series tire

Question
have 2008 envoy full package has 60 series tire on 18 inch rims want to know if i can switch to 70 series tire on same rim for better gas mileage

Answer
Peter,

I go into a whole look at tires and fuel economy here:

http://www.barrystiretech.com/rrandfe.html

and here:

http://www.barrystiretech.com/rrandfe2.html

Bottonline:

Fuel economy has more to do with careful selection of tires than the improvement you get from changing tire size.  You'd be further ahead selecting a tire with good rolling resistance.

However, General Motors does a really good job of balancing rolling resistance, treadwear, and traction - so unless you are unhappy with one of those properties of your original tires, your best bet is to stick with the original tires - size, make, and make