The problem is with testing methodology - NEDC, which consist of separate endurance distance test and separate dynamometer test.
Not only do the automakers make cars to get the best results in this methodology (which usually means worse fuel economy in normal traffic use - downsizing is a classic example, with low paper values which can double if you’re not careful with your right foot - if I’m not careful with my 1.4MPI atmospheric engine I can get maybe 1-2l/100km more, with small turbo engines it can be 4-5l/100km more), but they actively use tricks to get even better results. Things like stripped down cars and low friction overpressured tires (which you wont find on the production model) for the endurance distance test and things like altered ECU and high ambient temperature (within limits) for the dyno test.
[quote=“07CobaltGirl”]My car gets (advertised) 34mpg (US) highway. This equates to 6.9L/100km, or 40.8mpg (imperial).
I actually get 37mpg (US) highway. This equates to 6.4L/100km, or 44.4mpg (imperial).
I know people with my car (who are hyper-milers) getting 50+ (US) mpg combined (60+ highway only). It’s all in how you drive it. I drive mine like a banshee most of the time (gotta love that exhaust note!).
Just for real world references. [/quote]
It also depends on where you live/drive. My Sonic Turbo is rated at up to 40 MPG highway. I do about 35% city driving, and average 31.5 MPG, using conservative acceleration and limit my speeds to 63 or below. I live in the Seattle Metro area, which is one of the hilliest major cities in the US. I know guys on the Sonic forums who live in flat states in the Midwest who regularly get 50 MPG. Guess if it’s all flat and wide open there’s nothing to tank your economy.
Then again, on a recent trip home from a camping trip in our Hyundai Entourage (rated at 24 MPG highway), we got 21 MPG in low rolling hills. Oh yeah, forgot to mention the 3000 pound camping trailer we were pulling behind us. I consider that a win.
But yeah, driver behavior and terrain will greatly affect overall fuel economy, which is why tests are devised to rate cars – in an attempt to be (somewhat) consistent.
As part of the rebalancing and polishing, we worked a bit more on the fuel economy calculations today and found that we’re using an older simplified model with the wrong exponent for the throttle vs. efficiency calculations. What this means is that powerful cars have much too good fuel economy, as you can see in the game right now. Also, we put in an additional penalty for high cam engines. Overall this gives much more realistic results now.
@vmo: in the example you mention, fuel economy would roughly double.
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