I have done a study last year about relationship speed and fuel consumpion, I wanted to share with valuable forum members. In the chart below from 2006 to 2008 model
yaris 1.3 1.0 and d-4d compared in 5. gear, constant air, straight path. So the fuel consumption has changed a lot. I have tested the theory in practice with
yaris 1.0 and I confirmed the chart
Not: The horizontal line = speed (km/hour)
the vertical line = consumption unit