Good luck with that.
You'll see 30 MPG on the motorway, if you keep to 60 MPH. Around my Cornish roads, mine was returning between 15 and 23 MPG, depending on how I drove it, but it averaged out at 18.9 MPG over 30k miles.
It's over in time, but well under in miles.
Maybe change them, if you decide you can cover the rather high fuel consumption. [/QUOH mlll