EPA MPG Estimates are Seriously Flawed

[GeneK]

The 1983, 1984 and 1985 Diplomat are essentially the same so I just used the 1985 numbers.

The thing is none of those fuel mileages use hypermiling techniques. Just moderate acceleration, run the speed limit and dont "charge" redlights or stop signs.

I almost always do better (compared to estimates) on larger more powerful vehicles and struggle to make the estimates on smaller less powerful vehicles.

[imzjustplayin]

Originally Posted by Tightwad

The 1983, 1984 and 1985 Diplomat are essentially the same so I just used the 1985 numbers.

The thing is none of those fuel mileages use hypermiling techniques. Just moderate acceleration, run the speed limit and dont "charge" redlights or stop signs.

I almost always do better (compared to estimates) on larger more powerful vehicles and struggle to make the estimates on smaller less powerful vehicles.

Sounds like to me you do a lot of highway driving.. Large vehicles with big engines are very capable of getting good numbers, so good it sometimes makes you question the value of those "smaller cars". However the strength of smaller cars tends to be in city driving since they tend to weigh less and therefore have less inertia. I mean I can get 38mpg in a Volvo S60 I drive which is rated at 22mpg combined, though I have to be cruising at 55mph. In a Honda Civic, cruising at the same speed and route, best I think I can get is 50mpg and that is rated at 30mpg combined. I've heard of at least one guy with a Buick Lesabre also getting 38mpg but I think they were driving faster than 55mph..

[trollbait]

The thing is none of those fuel mileages use hypermiling techniques. Just moderate acceleration, run the speed limit and dont "charge" redlights or stop signs.

For the average driver, those are hypermiling techniques.

[GeneK]

Originally Posted by trollbait

For the average driver, those are hypermiling techniques.

Hypermiling to me means. Pulse and Glide, Costing with engine off, Rolling out of throttle on up hills to barely crest hill, using gravity to accelerate, windows up with no ac in 80F+ Weather, drafting, never using a drive through, engine off at redlights. 40 mph max speed to optimize fuel mileage in high drag vehicle, etc.

I think my 15 mile and 25 minute commute should best be described as suburban. The lights are every 1/4 to 1 mile instead of every 100 yards.

I dont know what Im doing wrong with the Accent. I just dont seem to get any better with it than the Mustang on the same commute.

[22over7]

I've just come across a 1980 EPA fuel economy certificate (on the internet) for a Datsun 280zx, 3 speed auto, 2 seater.
It's the closest thing to my model I've found so far, the main difference being mine is the 4 seater and therefore a bit heavier.
The fuel rating is 19 mpg.
My fuel economy (before hypermiling) ranged from 20.8 to 19.6 mpg (spirited driving) and my last tank returned 22 mpg.

So yes, these ratings are only a guide. Even driving like a rat bag I was slightly above their figure.
The disclaimer reads "Your own mileage may be poorer depending upon options, driving conditions, your driving habits and your car's operating condition."

[imzjustplayin]

Originally Posted by D.O.G.

I've just come across a 1980 EPA fuel economy certificate (on the internet) for a Datsun 280zx, 3 speed auto, 2 seater.
It's the closest thing to my model I've found so far, the main difference being mine is the 4 seater and therefore a bit heavier.
The fuel rating is 19 mpg.
My fuel economy (before hypermiling) ranged from 20.8 to 19.6 mpg (spirited driving) and my last tank returned 22 mpg.

So yes, these ratings are only a guide. Even driving like a rat bag I was slightly above their figure.
The disclaimer reads "Your own mileage may be poorer depending upon options, driving conditions, your driving habits and your car's operating condition."

Your 280ZX is rated at 21city 26hwy, 23mpg combined; CAFE.. Which means its 1985-2007 or 2008+ fuel economy rating is significantly lower than that.. If you're able to average 23mpg doing 45% highway 55% city driving without ANY hypermiling techniques, then you're doing very well..

http://fueleconomy.gov/feg/download.shtml
001 3806015042 3 21 26 23 1107 168A3-1 6 FIAY 20.5489 26.1966 22.7566 6 280ZX 2+2 (FFS)

An approximate conversion... 22.5mpg CAFE=17mpg 2008 estimates, 20.5mpg CAFE=15mpg 2008 estimates, and 26mpg CAFE=19mpg 2008 estimates. So I guess using the 2008 estimates, your car is rated at 15mpg city, 19mpg hwy and 17mpg combined.

[22over7]

Originally Posted by *************

Your 280ZX is rated at 21city 26hwy, 23mpg combined; CAFE.. Which means its 1985-2007 or 2008+ fuel economy rating is significantly lower than that.. If you're able to average 23mpg doing 45% highway 55% city driving without ANY hypermiling techniques, then you're doing very well..

http://fueleconomy.gov/feg/download.shtml
001 3806015042 3 21 26 23 1107 168A3-1 6 FIAY 20.5489 26.1966 22.7566 6 280ZX 2+2 (FFS)

An approximate conversion... 22.5mpg CAFE=17mpg 2008 estimates, 20.5mpg CAFE=15mpg 2008 estimates, and 26mpg CAFE=19mpg 2008 estimates. So I guess using the 2008 estimates, your car is rated at 15mpg city, 19mpg hwy and 17mpg combined.

WOW!! Thankyou so much for that. I've been looking for fuel economy figures for this car for ages.
I didn't explain myself too well in my previous post. The pre-hypermiling figures were from two years ago, when I first bought the car. The 22 mpg is from this month, I haven't kept records inbetween.
Is there a particular formula for converting the "old" ratings to the "new"? I'm curious to see the different ratings for the life of this model.
Thanks again,
Pete.

[theholycow]

Boy am I glad to see that link and that interpretation of data! I couldn't find that link anymore, and I really wanted a way to get some kind of estimates for my car.

It looks like you're using 75% of the rating from 81FG.DAT.

From 80FG.DAT for the only LeSabre 4.1 listing I found:
100 4440 8030 6 17 23 20 794 252A3-1 6 4AY 17.3891 23.2655 19.6190( 4.1L) 7 LESABRE

Looks like my 2008 EPA rating would be around 13 city, 14.5 combined, 17.5 highway. BRB putting that in my garage data...

[Zalittle]

I may be wrong about this, but I heard that vehicle manufactures base their MPG on a vehicle doing 55mph on flat ground. Which may be why under different conditions you get lower MPG.

[theholycow]

Manufacturers base their MPG on the very specifically documented tests that the US EPA requires (and the EPA spot-checks to keep them honest).
http://fueleconomy.gov/feg/how_tested.shtml
http://fueleconomy.gov/feg/fe_test_schedules.shtml