wedge357

Just saw it on CBS "The Early Show" today. A Consumer Report-backed investigation on how accurate mileage ratings shown on new car stickers. Apparently highway mileage ratings are pretty accurate but there are significant discrepancies when they tested for city mileage. One example was the Toyota Prius, EPA city mileage is 60mi/gallon but the test only came up with 34mi/gal. A full-size domestic SUV (I forgot the make) only made 7mi/gal instead of its stated 15mi/gal rating! They also showed figures for Honda Odyssey, Toyota Camry, Ford Focus, among others and they all came up quite short from claimed city mileage ratings. The Early Show report then showed an interview with a high-ranking woman from the EPA who admitted that a more accurate testing procedure is in the works to more correctly portray real-world mileage.

I guess what this all means is that Mazda did not fudge their EPA mileage rating afterall but is because of flawed testing procedure as mandated by the EPA. So for those people who thought driving their second cars might save them gas, you might have to think again.

Discuss.

psbjames1970

Great story... I wonder if the EPA factors in traffic jams. Something tells me they dont account for a high amount of stalled traffic normally encountered in a typical city environment. Especially at rush hour.

FoxTypeR

The only time you can accurately produce the stated "city" mileage as tested by the EPA is on a relatively cool day, with no humidity, no traffic, and maintaining a constant cruising speed of somewhere around 35-40 mph in your tallest gear with little to no stops. Your car has to be properly warmed up and have very little weight in it. Also, you have to be on flat surfaces. The only time I've every met the EPA regulations on a car I had was in Lubbock, TX about 7 or 8 years ago, when traffic was still light enough to produce the above conditions.

I'm curious to find out if a newer, more "accurate" EPA test were to come out, how many of the new cars sold today would be slapped with a gas guzzler tax.

wedge357

LOL good thing we already have the 8!

Roaddemon

Don't forget no wind resistance too.

SantozRx8

ive got a saturn as well and its claimed at 25mpg city and i get well over that each time (spirited driving), one time i drove like a granny and got around 31 mpg city

rx8wannahave

I've heard this many times before but I have never failed to get the EPA numbers so I don't understand what the problem is. I actually always beat the EPA city numbers...

In my Probe GT (22/26) I use to get 24 in all city driving
In my RX8 (18/24) my ownership average so far is 19+ in all city driving with the worst fuel economy comming in at 18.7 or .6.

So...I don't personally get why people can't hit those numbers other than blaming the people themselves or maybe some faulty RX8's. Just my .02

wedge357

Well good for you then... All the cars mentioned in the show came up well short of their stated mileage. Saturn maybe an exemption then...

wedge357

I think what we can get from all this is that not all so-called "city" driving are the same. So when some JoeSchmoe complains that his RX-8 can only get 12-15mpg while driving in Whereever City, USA we can't really say it's due to having a faulty car. It may well just be because his city driving is different than yours and mine...

Gambit

Lucky bastard

I usually got 16-17 all city driving. Currently gettin 22 50/50 highway/city

KYLiquid

As it has been stated on this forum before, the EPA test DOES account for the car being cold, stoplights, crawling in traffic, ect, for its city tests, and open highway cruising for its highway tests. Part of the problem is the cars are tested in a lab, not on the road. So as it was mentioned above...the cars are in a climate controled building so the intake air can be at optimum temp/humidity and there is also no wind resistance...even so...the real problem with the EPA numbers are that the AVG and MAX speeds durring the tests are not up to par with the real world.

Some of the things from this article (http://www.aiada.org/article.asp?id=29828) point out the problems with the test. :



Low highway speeds. The EPA test assumes an average car speed of 48 mph and a maximum of 60 mph. Most state highway speed limits are now set at 65 mph or higher. At those speeds, fuel economy can drop by almost 10 percent to 17 percent, compared to 55 mph.

Easy acceleration. The maximum acceleration rate is 3.3 mph per second, or equivalent to taking about 18 seconds to go from 0 to 60 mph. By the EPA’s own data, most drivers today accelerate nearly five times harder. The harder the acceleration, the more gas wasted.

Overestimated trip lengths. The EPA’s "city" tests assume a trip of 7.5 miles. But even recent EPA figures show the average urban drive lasts five miles or even half that, at 2.5 miles. Shorter trips mean car engines do not have the time to warm up and operate efficiently.

Exclusion of air conditioning and other accessories. Rare luxury items 30 years ago, air conditioners are practically standard features on nearly every new vehicle in the United States. Heavy use of air conditioning and other accessories mean a severe reduction in fuel efficiency -- especially in stop-and-go traffic conditions.

I tell people "Dont use the EPA miliage to try and calculate the MPG you will get driving or what it should cost (in fuel) to drive the car", "use it to compare cars to each other, since its safe to assume that the way the cars are tested doesnt work in the real world...so the data is usless to you on the road....but since the cars were all tested under similar conditions...you can compare them, and assume that driven the same way on the street you could figure how much one would cost over the other...."

For example : If car A gets 22/28 and car B gets 18/24, its a pretty sure bet that car A is gonna get better miliage, prolly by close to 4mpg better than car B. That might not mean you get the exact EPA numbers.....but it might looks something like car A 18/24 and car b getting 14/18.

we know that in the lab car A got 4mpg better than car B, so on the street, driven in a similar fassion/similar conditions to each other....they would most likely be 4mpg apart, for whatever they get.

Now this might now be 100% true...its just an example... but it is one way to use the EPA rating that wont leave you pissed off.

Glyphon

it seems as if those that have very short drives and/or those sitting in lots of heavy stop and go traffic seem to get the worst gas mileage.

Glyphon

another thing to note about wind resistance...for every 5mph over 65mph, you loose 1mpg in efficiency... inother words, say a car doing 70mph gets 20mpg. it then speeds up to 80mph. its fuel economy has effectively dropped to 18mpg.

spork

This car is pretty weird if you ask me.

I can drive like 60 city/40 freeway and keep my RPMs under 3.75K (mostly around 2.5K) and get like 18mpg. I used to get like 16 though (change in driving habits increased it by around 2mpg). But just this weekend I took a trip to San Diego. 80 miles there, 80 miles back. On the way there, there was much traffic. It took me like 2 hours and 20 minutes to get there. A lot of stop and go. On the way back, I was going like 85-90 mph back (was above 3.75K rpm all the free way driving). Trip took me around an hour (maybe a tad less or a tad more).

I initally expected to get like 22 mpg before I saw how bad the traffic was going down but I still got 20mpg. (19.9, dammit, I've only got over 20mpg once and that was only off a quarter of a tank!).

So yeah, it seems to me that the length of your trips matter more than how much you stop/go and what your RPMs are at (provided it's within reason) since everytime I take a longer trip, I get near 20mpg even if the longer trip is through not so nice traffic.

dwynne

This is not "news" - just about anyone that has purchased a new car with an EPA sticker in recent years knows that they are wrong. Everyone that has ever purchased an RX-8 knows (or finds out quick) that the number is wrong.


CR found that 90% of the cars tested do worse in real life and can't match the EPA numbers. 10% could match or even better the EPA number.


Our study found that only 10 percent of vehicles achieved fuel economies as good as or better than EPA estimates, including the 2003 Infiniti FX35, the 2004 Chrysler Crossfire, and the 2000 Honda S2000 convertible.


Not to defend the car makers, but by law the only number they can give out is the EPA number. So even if they KNOW you are going to get worse mileage, they can't tell you ("23 mpg city, but really expect 15 mpg" for example). You have to read the road tests and talk to other owners to KNOW what to expect.

I have posted about the EPA test procedures before and how flawed they are - the max speed on the highway test is 60 and the average is 48.3mph. How "highway" is that? Since they are done on a chasis dyno there is no wind resistance so a "brick wall" would get the same EPA number as a slick coupe with the same powertrain.

The city test is not much better for being realistic and note the "no AC" part.

EPA Test proceedure

Dennis

gh0st

i have NEVER seen more then 190miles before fuel light comes on. and that was driving it and shifting at 4.5k. i have babied it and shifted at 3k before and only got around 180miles. i drive almost entirely local though so i havent really been able to test highway mileage.

on the other hand. i have the weakest rx-8 i have ever driven (about 7 of them now) by a pretty huge margin. my dealership refuses to acknowledge that there is a problem.

denward

wedge357

weak acceleration plus low mileage? Sounds like your PCM maybe dumping too much fuel to richen the AFR. The computer is supposed to do this to lessen cat temperature but since all Renesis engines are handbuilt yours may be getting more fuel than would be needed thereby causing all your symptoms. If this is the case your best bet would be to get one of those piggyback ECUs like the Interceptor-x so you can fiddle around with the Air-Fuel mix.

dmp

My ProbeGT's economy Before turbo was nearly the same - low-mid 20s in town, mid-high 20s on the hwy.
After turbo, mid 20s in town (worst mileage was 12mpg, best was 24), and high 20s on the hwy (best was 28mpg on a road trip).

My RX8 now gets a SOLID 18mpg in town...and has gotten as good as 21mpg on the hwy.

MTCD01

I don't really understand the problem either...

My 8 get 12.5 MPG city (I'm now up to 14.6 MPG with Grandma style driving - hardly worth the aggrevation since the increase only yields 26 extra miles between fillups) and 22 MPG Highway (avg speed of 90 MPH - close enough to EPA estimates IMO).

I'm perfectly happy with the highway mileage but the city driving that I do (everyday commute) is killing me.

If this were true then my car at 65 MPH on the highway should yield 27 MPG...that is 3 MPG better than EPA estimates. If I were to then turn off the AC I might get near 30 MPG.

rx8wannahave

Yeah and the persons driving habits too.

KY good info...post

dmp...that Probe GT was a pretty good car huh, I had my fun with it but I only wish I had it new. If they would have given it 215HP and made it RWD that car would still be around today. It was a SOLID sports car...for a FWD, but it's name does not give the public nice dreams...lol

~)(

My first car was a Probe SE (AT). It handled exceptionally well for what it was, but I had tons of issues with the car. I had my transmission replaced 3 times in under 2 years!!! 3 TIMES!!! By the way, it shares the same engine as a Mazda 626 -- maybe that's the only reason why I liked the car!

-jc

Aseras

the epa doesnt actually drive cars at all. they park the car and run it through a "simulation" ( rev engine idle and maintain certain speeds and acceleration ) and measure emissions and gas used and that's their test.

Aseras

ask em to do a compression test...

frequentflyer

Also, I expect the EPA tests use gas without ethanol. Why the public wasn't outraged by the addition of ethanol to gas is beyond me! Over many years of keeping track of gas mileage in my cars, I have documented that gas with 10% ethanol reduces my gas mileage by at least 15%. Sometimes it's more.

The trouble with city gas mileage is that the cities with the worst traffic jams almost always have air quality problems and therefore require ethanol in their fuel. So we get a double-whammy. We already would get bad gas mileage because of the city driving, but now we're forced to get even worse gas mileage in the name of saving the environment. Except I don't see how we're saving the environment when ethanol makes us use more gas than we otherwise would! (I guess it's supposed to reduce emissions, so we get cleaner air but at the expense of using more fuel. I don't quite understand that tradeoff....)

I remember in the pre-ethanol days that our cars would routinely get better gas mileage than what the EPA estimated.

How many of you have paid attention to the effect of ethanol in your gas? Have you seen the same MPG reductions that I've seen?

rx8wannahave

I"m just glad we don't have Ethanol in FL...