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Old 07-04-2007, 04:50 AM
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bwilson4web bwilson4web is offline
Engineering first
 
Real Name: Bob
Location: Huntsville, AL
Hybrids: Prius Classic 03
Posts: 5,029
Thumbs up Re: MPG vs Speed - Hybrid driving strategy

Quote:
Originally Posted by jrb_nw View Post
Great points Bob - thanks. I do find myself taking surface streets across town more frequently, and find it relaxing and pleasant while the commuters are all slogging it out on the 4-lane. And it helps my average mpg, too!
Actually I want to thank you. When you posted "normal driving" it reminded me of the abnormal performance of gas-only vehicles.

Vehicle drag follows a fairly simple formula:

drag = (coeff_of_drag * velocity**2) + rolling_drag

This means a speedier vehicle goes up faster than the speed increase by the velocity squared. The Prius and similar hybrids follow this natural law and deliver better City MPG than Highway MPG.

In contrast, Gas-only cars have worse City MPG at low speeds. This is more than just the lack of regenerative braking but also includes operating the engine in inefficient rpm ranges. Internal combustion engines are terribly inefficient at low speeds and though diesels are less bad, they have problems too.

Your comment helped me realize that our hybrids are "normal" because their performance follows the laws of nature. In contrast, ordinary vehicles perform counter to the laws of nature.

Thanks,
Bob Wilson

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