What is the fuel economy, or UNeconomy, on a "C".

So far on a month long trip pulling a dinghy it's been a low of 12 MPG and a high of 15+. Hills and aerodynamics affect it a lot. In states where I can only do 55 I get better mileage. Here in Utah driving on the freeway at 48 (as one poster is) would be dangerous. There are 80 MPH speed limits here. That would be a 30MPH delta in speed. I'm doing 65 and still going slowly relatively speaking.