Now that's promising, how many do you have on the clock at the moment? There's definitely a sweet spot for MPG lower down the speedo, I see your average was around 30mph but how fast were you cruising? I'm guessing 50-60?
About 60mph is the sweet spot for best mpg most driving conditions – fast enough for the engine to be comfortable in 6th gear in all conditions without having to rely on putting a disproportionate amount of fuel in to maintain high torque in any situation to keep you in 6th e.g. going up a hill etc, the engine will be doing about 1650 revs. The air resistance is still pretty linear with speed up to 60mph, after that the car starts to require disproportionately more effort to overcome it as the speed increases. Traditionally 56mph was the optimum speed for fuel economy, but for a high geared TDI, it’s a bit higher than that as I’m sure you wouldn’t take a really steep hill in 6th at 55mph, doing only 1500rpm, you’d end up knocking it down to 5th, but on the flat, 55mph/6th will be great for mpg.
There are times when knocking down a gear will yield better mpg. I find that even though my GTD is happy to sit in 6th to do a constant 40mph, 5th gear is more economical for me than 6th up to about 43mpg on the flat and maybe up to 50mph up a moderate hill. The gear change prompt doesn’t seem intelligent enough to always give you the right answer – it seems to take only gear and speed into account, rather than engine effort in certain situations, although it does seem to tweak the speeds for gear change up when the car is undergoing an active regen.
