you got more than me

what kind of road you usually drive on? I commute to work, 10 miles each way combining some 40mph zone, some back roads and some 30mph zones, and usually gives 35mpg.
On a longer run, some A road for about 40 miles, a round trip gives me 40mpg.
One thing I found, the 17 inch alloy, though looks good, could be quite unforgiving on bumps or potholes.... we got loads of this in my part of the country, is the 16 inch alloy better?