Ask MetaFilter questions tagged with fuelefficiency

Mythbusters vs. Common Sense part 2371213

tehloki — Sun, 25 Oct 2009 17:10:26 -0800

Why aren't cars dimpled like golf balls if it increases fuel efficiency? In the most recent episode of Mythbusters, in testing the "a dirty car gets better mileage" myth, they seem to have proven that a car which has been dimpled like a golf ball gets better mileage than a car of the same weight and general shape without dimples. I'm aware of why other aerodynamic surfaces like airplane wings aren't dimpled, but with this empirical evidence of the benefits of dimpling (and the results of other similar experiments which have surely been done at some point), why aren't the bodies of cars dimpled? Is there a scientific explanation for the lack of dimpling on modern cars or one rooted in economics (time and manpower required) or aesthetics (ugly car)?

Does the optimal speed for fuel efficiency vary by car model?

scblackman — Fri, 11 Jul 2008 07:24:14 -0800

What is the optimal speed for fuel-efficiency for my car? Do I really have to drive 55? As I've been listening to the increasing buzz about resurrecting a national 55 MPH speed limit, I starting thinking about where that number came from, the types of automobiles in use at the time the number was derived, and whether it is still applicable today.

From what I understand, above 55 MPH is the point at which wind resistance increases drag enough to cause a disproportionate increase in the amount of fuel consumed in order to move the car a certain distance. Of course, that was what we were told in the 1970s when people were driving Lincoln Continentals and El Caminos. Cars today are supposed to be engineered to be more aerodynamically sound, thus less drag.

So my questions are these:

- Does the optimal speed for fuel efficiency vary by car? Will my Honda Fit be just as efficient at 65 than at 55, where a Land Rover won't?

- Are there any sources of data (tables, etc.) by car model that would have this data?

- Are there other factors that I'm missing besides, wind resistance, that contribute to fuel inefficiency at speeds greater than 55 MPH?

90 vs 60 and Bugatti vs Nissan

revmitcz — Tue, 29 Apr 2008 17:26:35 -0800

Help me solve two MPG (and car) related arguments (quick side-note, neither of these are serious "OMG UR SO DUMB!" arguments - more like random musing. Though, the first argument has very practical applications)

Argument 1 :
I read this article stating that peak fuel efficiency is at 55-60MPH - and that you lose 5-7% efficiency per 5MPH over that. Using cruise control, obviously, increases that even more. My current car won't let me use CC above 90MPH.

But, my argument (really more of a question) is that if I drove my car from, say, LA to Phoenix (375 Miles, est) at 90MPH vs 60MPH, I'd ultimately help the environment because I'd be on the road for about an hour and 40 mins less time.

Does that make up for decrease in fuel efficiency, or no?

Argument 2 :
I was laughing at the MPG estimates on the Bugatti Veyron - which are 6MPG city and 10MPG highway. Going it's top speed, it would run out of fuel in just under 13 minutes. Of course, one would have traveled roughly 55 miles.

This lead to me saying "that means my piddly 6-speed 2.5L Altima could probably take a Bugatti Veyron on a race to Phoenix from LA" to my friend, who's got a hard-on for that Bugatti.

The best math I had to support it (and I suck at math) is this :

LA to Phoenix = 375 miles.
Bugatti Veyron @ 253 MPH = 1.5 hours
Nissan Altima @ 140 MPG = 2.6 hours.
Bugatti makes 7 stops for gas = add about 70 mins
Altima makes (maybe) 1 stop for gas = add about 10 mins.

Totals :
Bugatti = 2.7 hours
Altima = 2.65 hours

This, obviously, assumes both cars could actually go their top speed the whole way. While the road is mostly straightaways (and let's suppose cops weren't a factor in this theoretical race), I still think one would have a much harder time maintaining 253MPH vs 140MPH.

My friend figures the Bugatti would win, hands-down, regardless.

So - which one would win?

Gas prices change but cars don't. What gives?

Dec One — Mon, 18 Feb 2008 09:19:17 -0800

Gas has been getting more and more expensive, yet cars have not been getting more fuel efficient. Why not? So in case you haven't heard, gas is more expensive than it used to be. If you don't believe me, look at this chart. In the first eight months of 2005, we saw higher prices than ever before, and also more volatility than ever before. Prices were bouncing all over the place, and nobody knew what to expect for the future. Then Katrina and Rita kicked gas prices into the stratosphere, and I remember the following (please correct me if I'm wrong):

Surveys showed that people were no longer uncertain about whether high gas prices were here to stay; they were.

News articles quoted industry experts saying that car manufacturers were going to build more fuel-efficient cars.

Car advertisements, which used to say "Buy the new Canyonero!" now said "Buy the new 14 mpg Canyonero!". As if they were hoping customers who hadn't thought about fuel efficiency since 1991 would forget that 14 mpg is not good. Eventually, of course, customers would catch on, and these mpg-touting ads would have to be backed by an actual fuel-efficient car. Or so I thought.

Two and a half years later, I have heard no news of the new generation of fuel-efficient cars, either on the market or in the pipeline (I'm not counting the Chevrolet Volt, which is a niche product that may or may not ever be for sale). In automotive engineering, there is a tradeoff between horsepower and fuel efficiency. As technology advances, carmakers can choose to add mpg or add horsepower, or add a little to each. Or, I suppose (again, correct me if I'm wrong), they could choose to take away horsepower and add a whole bunch of miles per gallon.

Given the increase in gas prices, you'd think fuel efficiency would be getting the attention in new car designs. But it seems like new cars have continued to emphasize horsepower. The 2009 redesigned Toyota Corolla is advertised as more powerful and more fuel efficient, but the fuel efficiency gains are slight. The 2008 redesigned Honda Accord is actually less fuel efficient than its predecessor.

I know it takes a few years to design and build a new car. Where is the new generation of fuel-efficient cars? Is it going to exist? Are there any new cars in manufacturers' pipelines that will cater to the segment of the cutomer base that doesn't care about horsepower too much, but wants a car that's really good on gas, and doesn't want to pay $5,000 extra for a hybrid? If so, when will I be able to buy one?