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Old 10-02-2020, 10:23 AM   #26 (permalink)
Ecky
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ND Miata - '15 Mazda MX-5 Special Package
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As mpg_numbers_guy said earlier, the Insight is a great point of reference. In stock form, using exreme LRR tires which sacrifice handling and traction, with the inflation pressure raised to 45+, and a few minor aero mods (partial grille block), the Insight is capable of 100mpg @ 50mph. As speed increases, that fuel economy drops significantly. I want to say that at 60mph, it's closer to 80mpg.

https://ecomodder.com/wiki/Vehicle_C...t_of_Drag_List

The Insight has a 0.25 drag coefficient (very low), a frontal area of ~20 sq ft (very low), and an engine whose peak thermal efficiency is just as good as the best from Toyota and Honda today (~40%) - albeit with a lower output than Toyota and Honda's current best.

My thinking is, you'll need an engine that is no less efficient than the Insight's, which is a very short list. You will also need to beat it in both coefficient of drag and frontal area. Diesel helps - the fuel contains ~15% more energy content, but you also usually pay more for it so it may not win in cost per mile.

If the goal is cost per mile per unit energy, going electric in an area with cheap electricity may be the easiest way to achieve this, but you have the upfront costs of the batteries.

From the Urban Centurion thread,

Quote:
Originally Posted by changzuki
The original Centurion reported 128mpg@35mph.
^ While that's impressive, drag increases with the square of the speed. Using a simple drag calculator, the drag at 60mph is 3x higher than at 35mph, while the speed has only increased by 70%. Meaning that, if drag is the sole difference between MPG at the two speeds (RR and mechanical loss stay constant), that 128mpg @ 35mph might be 75mpg @ 60mph. Still very respectable, but the decently aerodynamic Centurion with its 37hp-at-the-flywheel engine is still well short of your target.
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