[cmb]

I am running 15" rims and 195 tires.

I've found the Insight to be the most economical running at 100-115 kph.
Anything more, and I tend to be relying heavily on substantial assistance from the electric motor as well as revving up or having to downshift for more passing power.

 

[windmill]

I've found the Insight to be the most economical running at 100-115 kph.

For me it is between 90 and 95 kph, my record was last summer at 80 kph and my Insight did 117 mpg/ 1:50 ltr/km for about 45 km's/30 mls long 8)

 

[james]

Whatever the semi in front is doing

Seriously, I've never found one particular speed that's most economical. It depends on things like slight up or down grades, head or tail winds, the road surface. Heck, maybe whether the spirits in that particular area decide to play tricks

There's one particular stretch of road, about 15 miles and absolutely flat, on which I can't get more than 65 mpg whatever I do, even though on similar roads, driving the same way, I'd be above 75.