Originally Posted by Dougie
There's been quite a bit of discussion about this in the past, although it might be hard to find it.
Basically you have to drive slowly--40 mph-ish--and not need to stop for intersections or traffic. No wind. Level roads. Hot weather. A longer trip cancels out the cold engine and initial acceleration at the start of a trip, so go at least 25 miles or so at a minimum... It should not be too hard with a manual transmission to break into the 100s for a round trip under these conditions.
Exactly, though a few things to add:
- up to 50mph-ish works well for me
- hot weather (and summer fuel) definitely helps, and longer trip (40 miles or more) to amortize the low mpg during warmup
- highway with no stops needed
- tailwinds obviously help, no wind is better than side or (obviously) head winds
- gently rolling terrain is better than dead flat: you drive up the uphills (without invoking assist) and then either coast the downhills engine-off (if they are steep enough) or drive down them in lean burn while getting a touch of regen to replace losses (electric steering is a biggie)
- higher tire pressures help because the car maintains speed better while coasting
- no drafting, but wakes from passing traffic do help, especially in a headwind
- I have MIMA but use it less extensively than many: mainly just to feed in extra regen here and there. And the FAS module makes engine-off coasting safer and more convenient, but key-off gives the same fuel saving.
That is how I got my 109.5 long distance trip last summer.
Obviously if the trip is overall significantly downhill that will increase the mpg, but my trip was not.