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Old 03-11-2007, 09:14 AM   #4
FrayAdjacent
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Join Date: Dec 2006
Location: Austin, TX
Posts: 939
I doubt LA traffic that crawls at a couple MPH would be very clean at all...


I used to have a Honda Insight a few years back, and it taught me a few things. One of which was what I call the 'sweet spot', which is the speed (highway) at which you get the best fuel efficiency.

This is a combination of things about a vehicle:

Mass
Speed
Aerodynamic efficiency (drag - can be affected by wind!)
Engine efficiency

Basically, every vehicle is going to have a point at speed where it will get the best fuel economy, then as speed increases, fuel efficiency drops. This is mosly due to the fact that drag DOUBLES every 10mph faster one travels. My Insight, although very light (1800lb) was VERY aerodynamic, and it's 'sweet spot' was at about 65mph.

If I bumped that up to 85mph, my fuel efficiency dropped about 25%.


Of course, it could get AMAZING economy at 35, 45 and 55mph... but above about 70, it starts dropping.

This same theory will affect ALL vehicles, but their 'sweet spots' will differ a lot.


And I'll cap it off by saying - I don't really buy into the whole 'global warming' crap that says we (humans) are causing it. The planet naturally goes through cycles, and we're probably just on a warmer upswing.
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