Fuel Economy


Dear Pablo,

Since gas prices have topped $4 a gallon, tips on saving gas have been the flavor-of-the-day in the media. But does driving slower really save gas? If it takes me longer to get there, isn’t my car burning more gas?

The short answer is that slowing down does increase the fuel economy of your vehicle. The reason lies in aerodynamics. What you need to know is this: As speed doubles, the force (aerodynamic drag) on your vehicle increases fourfold. For example, a house built to withstand 200 mph wind has to be four times stronger than a house built to withstand 100 mph wind. The formula for aerodynamic drag on your vehicle takes into account how aerodynamic it is, what the area of its cross section is, what the density of the air is, and what your vehicle’s speed is. Since you can’t influence the density of the air, and you can’t change your vehicle’s aerodynamics, that leaves only speed. And slower speed equals less drag. (more…)

thumb_CowIt is once again time to explore the wonderful world of sustainability metrics. This week I am going to tackle the myth of the meat-powered cyclist. Here’s the story: A friend of mine once told me that it is more efficient to drive a car over a certain distance than to ride a bike over that same distance if your calories come from beef. Before passing on this great anecdote on the inefficiency of beef production I thought I would run the numbers myself. Join me this week in another exciting installment of Ask Pablo. (more…)

 
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