http://www.greencarcongress.com/2006...onsumptio.html
Amazing. Going 150 mph will drop fuel economy of a diesel to about 10 mpg, when you might normally get 35 mpg at 60 mph in that same car. Gas cars are no doubt going to be worse.
It might be a fair estimate that a gas car that normally gets 25 mpg at 60 mph might only get 7 mpg at 150 mph.
The above hypothetical car with a 15 gallon tank would have a 375 mile range at 60 mph, and a 105 mile range at 150 mph.
In contrast, if an electric car were made that could go 150 mph, it might get 250 miles range at 60 mph with a 60 kWh Li Ion battery pack, and might only get 30 miles range at 150 mph.
A typical gas powered car will have an engine about 10-12% efficient in normal use, rising to 25% efficient if its maximum load is used. This is why vehicle efficiency and range don't drop as sharply as a similar electric car as speed increases. Even still, an EV would be much more efficient overall, with an electric motor still being 60-70% efficient at full load, while in normal use it might be 80-95% efficient.
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