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Yes 70km/hr will give the best FE IFF you don't have a lot of hills, I was able to average over 30mpg with my buick most of its life (and this included in town driving). With several 35-38mpg tanks on the car (very slow and very challenging)
Trouble is you have very little cushion if there are hills and the car will downshift if you are riding the edge of gear change, this isn't a game ending consequence but if it happens OFTEN it will ruin any gains you get from the low speed.
Generally if you can VERY VERY gently and slowly move the throttle in as you go down hills (accelerating) and very slowly and gently move the throttle out decellerating up hills when you can get away with it will give the best overal FE. A close 2nd is to hold the throttle in ONE position and never move it regardless of speed with the exception of when you are nearing the downshift point.
With mixed hills and whatnot 45-50mph (approx80kmh) (US) gives the best FE as long as you don't punch the gas going up the hill and let the car bleed and gain speed with hills.
95kmh will reduce FE on flat ground in most cases, its fine if you are going downhill though.
MUCH MUCH easier with some sort of guage to look at and you will see what I mean. I could easily exceed 32mpg (US) using these techniques, I always wanted 40mpg but its downrite impossible without some sort of mod like a manual transmission swap or ECM tuning or a block/air dam.
Another helpfull hint is that most people give too much gas on flat ground and don't realize it. A very small excess amount of throttle will not make the car move notably faster but it will make you loose 2-5mpg.
The way I've gotten around that for over 15years is to move the throttle all the way out then push it back in until I just maintain speed. Don't worry if you loose a little speed, just make sure you are a bit over the speed you need to go so you can settle into a safe slow HI FE speed without downshifting.
Good Luck
Ryan
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