2 In 3 Misunderstand Gas Mileage; Here's Why

thecarchik sends in this piece, which was published last March but remains timely: "OK, so here's a little test: Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg? If you're like most Americans, you picked the second one. But, in fact, that's exactly backwards. Over any given mileage, replacing a 10-mpg vehicle with one that gets 20 mpg saves five times the gasoline that replacing a 33-mpg vehicle with one that gets 50 does. Last summer, Duke University's Fuqua School of Business released a study that shows how much damage comes from using MPG instead of consumption to measure how green a car is. Management professors Richard Larick and Jack Soll's experiments proved that consumers thought fuel consumption was cut at an even rate as mileage increased."

Comments

Re:MPG and GPM are both useful

[JesseL]

High octane equals higher resistance to uncontrolled preignition (aka knock, or detonation). Higher resistance to preignition allows more advanced ignition timing. More advanced ignition equals higher cylinder pressures and longer burn duration. Higher cylinder pressure and longer burn duration allows more complete combustion and higher efficiency.

Modern vehicles with knock sensors can get greater efficiency from higher octane fuels due to their ability to keep ignition timing as advanced as possible without running into preignition.

Re:3 people in 2 don't know math.

[twistedsymphony]

Except that the American government already tells you the consumption as well as the MPG for every car sold in America. Go visit FuelEconomy.gov

They tell you not just the MPG, but

• the average cost per mile
• the average annual fuel cost
• the average cost to fill up
• tank size
• mileage range on a single tank
• average consumption per year in barrels
• Annual Tons of CO2 Emitted
• .... other crap you might care about

it even has calculators so you can plug in your own average miles traveled and driving style and determine how that effects the above.

also on there has a "garage" feature where you can have your cars and plug in how much you paid for gas and how many miles you got per gallon. (you don't even have to do the math yourself) and it will plot your mileage and allow you to compare what you're getting against the car's listed ratings as well as other drivers with the same car as you. I've got complete gas mileage charts for ever car I've owned over the last few years thanks to that site.

The site was created by the American government, it's been around for years, and it's openly available to any American smart enough to conjure the phrase "Fuel Economy" and plug it into Google.

Not everything needs to be stickered to the damn car... I'm sure you friendly neighborhood car salesman would be happy to give you the sheet that explains all this information about the car too. Don't assume that the only information available is only what's fed to you in TV ads...

I have used this site to track my last two cars

[Shivetya]

and will be using it to track my latest.

The first car I tracked was a 2007 Civic Coupe EX, manual transmission. The second was a 2008 Mazda Miata SE. Without bouncing to the site to check the Miata was rated at 21c and 28h. In my two years of recorded mileage I never fell below 27 in a mix of city and highway travel; I have a 26 mile commute mixed between 35 and 55 with no interstate. I peaked at 33 during summer months and fell into the 27 range during winter where besides the cold requiring the engine to run rich I needed the compressor to run the defroster.

My newest addition, a 2010 VW Golf TDI with manual transmission shows that others have never been as low as the EPA predicted mileage which is 30c and 41/42h. I have yet to finish my first tank and the car's computer shows 38 miles per gallon.

Why all the fuss? Well the facility is there and it gives me a nice reference to see how my car reacts to seasons and how it reacts to age to include over all miles traveled. It provides a nice little log so I can also see fluctuations in fuel prices without having to rely just on my memory; like what was the price of gas in June 2008.

While many cars are not represented it does appear those with cars known to get good mileage do post their numbers more often. I have been surprised while browsing some vehicles to see just how low the mileage ratings are for many popular sedans, in many cases not better than many SUV/CUV types that people love to vilify.

In the rest of the world

[AliasMarlowe]

Outside the US & UK, fuel consumption for cars, trucks, etc, is normally expressed as Liters per 100 kilometers. This completely avoids the non-issue that TFA is grumbling about, even for innumerate consumers, since the numbers represent fuel used in a trip of 100km.
10 miles per US gallon = 23.52 L/100km (mind-bogglingly bad)
20 miles per US gallon = 11.76 L/100km (very bad)
33 miles per US gallon = 7.13 L/100km (OK for SUV, not so good for a car)
50 miles per US gallon = 4.7 L/100km (good for medium or large car, not so good for compact car)

FWIW, my Mercedes diesel stationwagon uses about 5.5 L/100km for mixed city/rural driving, which is 42.8 mpg(US) or 51.4 mpg(UK).