I'm not sure I would call it negligible when such tires are used on a Prius. The real problem, however, is that you replaced the most fuel efficient 17" tire we know of with a non-LRR tire. You got hit thrice. Once for the new tire effect which almost always produces a loss (temporarily), once for the non-LRR tire and a third time for using an aggressive performance tire. Unless you are racing, I would return the tires for something more appropriate for the Prius. Look for a LRR Grand Touring tire with a higher UTQG rating. Bridgestone Serenity Plus, Primacy MXM4, PureContact with EcoPlus, Ecopia EP422 etc etc.
not to start a new thread . because my question is relevant to this topic . how will a 195/60-16 or 205/55-16 on a light weight wheel fair against the oem 195/65-15 ? for the record the wheel is 16x7 and only 14lbs . any body have experience with this size and fuel economy ?
All that has said and done, what about the effect of a smaller wheel and tire set, say a 185/75/14 tire, which has the same diameter and load rating?
Weight of wheel and tire is not a factor, If I drive by myself, I'm getting about 47mpg, If I drive with one or two other my mpg is the same, even though I have added 150-300 pounds to the weight of the car. the whole car takes the weight and evens it out as to just placing it on the drive system. One way to test this is to put heavy wheels and tires on the front for 400 mles, then move them to the rear for 400 miles, see if things change...