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Originally Posted by Old Mechanic
I get the same mileage at 55 on a deserted US Route 60 as I do at 65-70 on the packed I64
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As SentraSE-R said :
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You can't fight the laws of physics.
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There's more drag at 65-70 than at 55 - be it aero, rolling, or mechanical. No way around that.
The question is how the car copes with that.
Old Mech's Fiesta will be in the same gear at either speed - so it can only be a matter of gearing and engine efficiency at the corresponding rpm.
Both are choices that Ford made when bringing it to the market, and since they don't cater for hypermilers, the Fiesta is likely geared to be at its optimum rpm somewhere around those higher, more
normal speeds.
Lower rpm is only OK if the engine can still pull it off OK.
It's not always or necessarily better - though you always win a bit by not having to accelerate the extra 10-15 mph.
Quote:
Originally Posted by basjoos
But you can modify them with effective aeromods to flatten out that drop in mpg with increasing speed
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Sure you can mod the hell out of a vehicle and reduce its drag, but it's still there - and increasing with speed.
From the speed / MPG numbers you've posted before, I recall that if you drive slower, you also get (even) better MPG.