Quote:
Originally Posted by mort
I think there is some misunderstanding coming from where this thread started. Gino Sovran of General Motors wrote a report showing how reducing aerodynamic drag would affect mpg figures obtained from the EPA testing procedures for a given car. The report makes the point that these changes would not be applicable to "real word" mpg. YMMV is all he meant.
The EPA tests are done on a programmable dynamometer. In order to have a dynamometer simulate the total road load of a vehicle, the dynamometer power absorber must be adjusted to reflect the road load characteristics of the vehicle. Most certification vehicles are tested using dynamometer power absorption values obtained according to the methods in the "EPA Recommended Practice for Determination of Vehicle Road Load." In this method the basic concept is to perform a series of road or track coastdowns with the vehicle. The coastdown measures the rolling resistance and aerodynamic drag in terms of varying deceleration. Coastdowns are then performed on the dynamometer at different power absorber settings, and the dynamometer power absorber adjustment is determined when the vehicle dynamometer coastdown time matches that of the road coastdown in a speed range of 55 to 45 mph. Since 1986 manufactures are allowed to use alternative methods to calculate road load, like using wind tunnel results to estimate aerodynamic drag ( see here).
Aerodynamic drag is included in the dynamometer load. The procedure is far from ideal, and modern equipment could give more accurate results, yet the EPA mpg figures are very close to real world numbers for most cars.
-mort |
Seems they are not so good with Toyotas, my Camry is 22mpg highway, back road country I averaged 27mph driving "normal" at 60mph before ecomodder. My corolla is something like 26mpg highway, and I pulled 33mpg on the highway going 75mph, alignment WAY off, bad tires/struts, etc. I get 40-45mpg with very little mods and slowing down now.
I can't seem to understand why the numbers are so way off. For example, the Camry, I went 70-75mph with a trailer behind it and got 22mpg and the car has 300k miles. Acording to the EPA, i should have gotten under 19mpg and 22 with out the trailer at all. Back then I was just a typical driver, didn't even think about saving fuel besides getting a smaller car for 30mpg+.