[beer]

Choosing the right size off tyres for better milage, is always a comprimise.
You have to look at which roads you drive the most.
If you drive alot on highways, then you better of with narrow, but large tyres.
The frontal area is less, less rpm's, less rolling resistance, but much heavier.

If you drive a lot in a city, you're better of with small, but a bit wider tyres.
Less unsprung weight, less rotating mass, but more rpm's.
Even better is when you use a bit widther rim then normal, becouse your tyres walls get
stretched and get stiffer, so you can take corners at greater speed.

And always look at the rolling resistance and weight of the tyre, becouse these differ between manufacturers

Michelin is the only tyre producer that i know of that doesn't only look at rolling recistance.
They released a few new tyres 10" sizes and a relative narrow 195/55r21 tyre.
Becouse they to confirm that it always a compremise between the two.