This is the best I’ve managed on a long journey - on the return trip I got 38mpg. BTW this was using ACC set to roughly 78mph. I definitely think the MPG suffers once you go over 70mph.

 

 

49 minutes ago, Ricey7000 said:

This is the best I’ve managed on a long journey - on the return trip I got 38mpg. BTW this was using ACC set to roughly 78mph. I definitely think the MPG suffers once you go over 70mph.

 

 

It sure does. Drag (air resistance) is a squared formula, meaning that when you double the speed, the resistance increases 4 times.

 

 https://en.wikipedia.org/wiki/Drag_(physics)

A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome aerodynamic drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula.

27 minutes ago, JanJan said:

 

It sure does. Drag (air resistance) is a squared formula, meaning that when you double the speed, the resistance increases 4 times.

 

 https://en.wikipedia.org/wiki/Drag_(physics)

A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome aerodynamic drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula.

 

Apologies in advance if I've missed something here, but if the horsepower quadruples shouldn't it be 40 hp (30 kw) ?

Trip to the office today and the trip home. Can't grumble at that to be honest, mixture of country lanes, winding A-roads and a motorway. Its uphill on the way home, so a 2mpg difference is OK. I'd venture the true figures are closer to 49-50mpg but still not bad for a 2-litre bus. (sorry about the blurry photo, phone rang as I took it)