Or to put it a different way, is the difference between 20 and 30 mpg the same as the difference between 30 and 40 mpg? Well, the difference is 10mpg, right? Maybe not. Let me paraphrase a Car Talk Puzzler to explain.
Buff Barry drives a rather big truck that gets roughly 8 mpg while his wife, Gentle Gina drives a Prius that gets near 50 mpg. Gina is interested in a new Smart car which gets almost 100 mpg* but Barry spoke to his mechanic who said that she doesn't need a new car and for a few hundred dollars he could adjust the timing and probably get Barry's fuel economy to increase to 10 mpg. Which should they choose?
[It should be noted that Smart makes electric cars, and is only used here because I couldn't think of a better car. Also, unless Barry's mechanic listens to car talk or is Matt Damon, it's unlikely he would really know the answer to this problem.]
The answer is that improving gas mileage from 8 to 10 is far better than switching from 50 to 100. This doesn't seem so, because we look at the values 2mpg and 50mpg and conclude that saving 50mpg is 25 times better than saving 2mpg. Think of it from this perspective: knowing that the average American drives 12,000 miles per year. If Gina drives that far in her Prius then she buys 240 gallons of gas. If she gets a new car then she gases up half as much and only buy 120 gallons of gas. Barry, on the other hand, is always at the pump. Getting only 8mpg, he buys 1,500 gallons to drive 12,000 miles. If his mechanic could increase his fuel economy by 2mpg (to 10) then he'd only purchase 1,200 gallons per year, saving him 300 gallons of gas.
So there it is. Increasing 2mpg for Barry saves him almost three times as much gas as if Gina increased her fuel economy by 50mpg. Interesting, but what does that really mean? That maybe the numbers are more important where we are least concerned. Tom and Ray give the Accord Hybrid a poor review because its fuel economy is much worse than the Camry and Altima Hybrids, specifically in the city. And while 7mpg is no small matter (average fuel economy is 27mpg for the Accord and 34 for the other two, 91 gallons per 12,000 miles driven), other comparisons may be lacking. Comparing four common trucks shows that apparently small differences in mpg are... well larger than they appear. The Lincoln Mark LT (Ford's luxury truck), Chevy's Silverado, the Honda Ridgeline AWD, and the GMC Sierra Hybrid average 14, 15, 17, and 17 mpg respectively. These small differences amount to 857, 800, and 706 gallons per 12,000 miles. Here 3 mpg difference in these trucks amounts to nearly double the 7 mpg difference in the hybrid cars.
So when is 10mpg 10mpg and when is it not? I don't know, but while trying to figure it out, read the government's suggestions on saving fuel.
3 comments:
But just think how much gasoline and time Barry would save if he would just get rid of his ginormous truck and get a Prius to match Gina's. There's the great math. Not "when is 10 not 10?" but "how can 8 become 100?" Answer: with a simple trade-in.
See, I read the whole thing :)
Zounds! This is cool stuff! My take is that I should just buy a Chevy Silverado cause that is what's best for 'Merica!
One thought I've had since writing this is how poor an effort is being made to save fuel consumption with hybrid engines. Maybe the entire hybrid market has been targeted incorrectly. It seems certain that the sort of consumer who wishes to save fuel is more likely to purchase a style of car that already sips fuel, but it also seems certain that saving 2 mpg on every truck, suburban, suv, sportscar and van being driven on American roads would do much more good than saving 10 mpg on every sedan and economy model.
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