Subscribe to the Free
  • |
  • |
  • Whale Watching: What's Wrong with Fuel Economy Ratings?

Whale Watching: What's Wrong with Fuel Economy Ratings?

G.R. Whale
Nov 17, 2008
Can we just drop CAFE, economy standards, and anything related to fuel mileage? Unfortunately, the EPA got this backward. The way it measures fuel economy--miles per gallon--is opposite to the way we measure everything else we consume.
Just about everything Americans eat, drink, burn through, plow over, spend on, or cover up is defined in "bigger numbers equals more," not "lower numbers equals more consumption." Not with fuel mileage, however, where vehicles that use more fuel are given a smaller number.
If we used gallons per mile (or 100 miles) instead, consumers might have a better understanding of what it takes to cover miles. (This is how Europeans express fuel economy--but in their case, it's liters per 100 kilometers.) A 12-mpg truck needs 8.3 gallons to go 100 miles, a 17-mpg truck consumes 5.9 gal/100 miles, and a 25-mpg truck just 4.0 gal/100 miles.
Our current rating system has other problems, too. While the methodology may have improved gasoline and ethanol accuracy, it still skews to hybrids and against diesels. Where the hybrids tend to get near their highway rating and fall a bit short of city ratings, diesels tend to exceed their city and highway cycle numbers. Read all about EPA testing on's quite amusing.
The EPA's test method is beatable to some extent. Limited full-throttle acceleration (the highest rate of acceleration is 8.46 mph/sec and you know even slow cars do the same test), or not fully opening the electronic throttle for the first three or four seconds, could help your ratings. Which could explain why some vehicles feel like they bog off the line in acceleration testing and come alive at certain rpm, but only in first gear.
Next, pickups and vehicles over 8500 GVW should be tested fully loaded, at Gross Combined if feasible, and averaged with the empty numbers. Better yet, also supply specific fuel consumption as used for marine and stationary diesel engines, given in pounds/horsepower-hour. You can buy a 310-horsepower Ram or a 390-horsepower Ram that rate the same, a 195-horsepower V-6 Chevy almost identical to a 315-horsepower V-8, or a Chevy 6.0-liter Silverado 2WD with numbers equal to a 4.0-liter Tacoma 4WD manual six-speed. Power requires energy, and using the power would give more accurate indications.
Bring back axle-ratio numbers. Manufacturers and the EPA no longer segment them, probably because it depends on environment. You'd have a hard time convincing me that a 4.10:1 axle gets the same highway mileage as a 3.23:1, all other things being equal.
Last, we should get the government out of it. I expect the SAE could do better for far less money; we already count on that group of engineers to certify power ratings.
Let's look at the old wives' tales about fuel economy. There are myriad lists of ways to save fuel, but even though they don't always apply to everyone, they still get repeated incessantly:
• Every 100 pounds of weight taken out equals a two-percent increase in fuel economy. Were that true, I could empty my fuel tanks and get 10-percent-better mileage driving on the fuel that was left in the lines. Since I've never measured an increase in fuel economy with one (300-pound) tank empty, I don't think that works. This may be effective in a light car, but in a 7000-pound pickup, dropping weight by less than two percent won't increase mileage by all that much.
• When driving over 50 mph, put the windows up and use air-conditioning. This is another generalization that assumes equal A/C performance and aerodynamic resistance. In a car with Cd of 0.27 and a truck with more frontal area and Cd of 0.41, opening the windows will add more drag in the car. At idle, engaging A/C in my truck drops engine speed 8-12 rpm from 670-675 rpm by optical tachometer. Opening the windows doesn't make any noticeable difference, either.
• Your fuel costs $0.30/gallon more per mph above 60. So if I start with $4/gallon fuel, my fuel costs have doubled at 74 mph, implying my consumption has doubled from 15 mpg to 7.5 mpg? No trip computer or measuring I've done indicates anything even close to that. Sure, speed increases drag exponentially, but this suggests opening the throttle a bit and upping revs doubles fuel use. I ain't buying it. Even the EPA says decreasing speed from 65 to 55 saves only 10 to 15 percent fuel consumption. It nets me seven percent in my truck, but costs me 1.7 hours on a 600-mile drive.
In other silly news, the St. Lucie County (Florida) Sheriff's department spent about $2500 in seized drug money on Hydro-4000 units that are said to increase efficiency by using distilled water to make hydrogen gas and net big mpg gains. If this were effective, Ford engineers would have been all over it. California has applied emissions controls to lawnmowers, even though most residential mowers run far less than smoke- and grease-spewing barbecues.
And, finally, in Geneva, Switzerland, you can text the government a license plate and get the owner name and address info in five seconds on your mobile, so when that Pagani goes by you, you'll be able to find the owner's house and see what he left behind.
Remind me to take a Truck Trend license plate with me the next time I go to Switzerland.



Subscribe Today and Save up to 83%!

Subscribe Truck Trend Magazine

Subscribe to:

Truck Trend

Subscribe Diesel Power Magazine

Subscribe to:

Diesel Power

Subscribe Truckin Magazine

Subscribe to: