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Old 12-11-2006, 07:15 PM   #1
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EPA Gas Mileage Estimates?

The window sticker on my `07 gives the EPA Estimated MPG as 23 (city) & 32 (Hwy). I was curious to see if these number had any relevance and at what speed. The City rating is somewhat ambiguous but the HWY rating can be calibrated with the vehicle speed. Resetting the MPG monitor I drove the car at 65 mph (2500 RPM in 5th) and got 32.2 mpg and at 70 mph (2750 RPM in 5th) I got 28.3 mpg, both averaged over about 5-10 miles of modest terrain in central NJ with the cruise control on. The car is only two days old with 600 miles so I was impressed as this is better than my ten year old Miata. Anyone have numbers to compare?

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Old 12-11-2006, 08:56 PM   #2
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Best digits I've received in my 2002 S is around 18 city with ave speeds in the mid 30's, and my highway has been as high as 32 with ave speeds in the low-to-mid 60's (6th gear in RPMs lower then 3K).

But I tend to drive her in the power range more then not - so mpg is out of the picture!

- C5150
2002 Boxster S
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Old 12-12-2006, 05:21 AM   #3
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I am getting 20-22 mpg in my 99 2.5. Normal daily driving in the 25 - 50 mph range.

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Old 12-12-2006, 06:12 AM   #4
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I've averaged 21.5MPG in the city since I've owned the car. Best mileage I got on a long trip was 28MPG, with the top up and sustained freeway cruising at around 75MPH.
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Old 12-12-2006, 06:47 AM   #5
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The EPA is using a somewhat antiquated method of determining Fuel Mileage Estimates which was defined some 25 years ago and not truly representative of today's cars or driving style. These tests were conducted in ideal laboratory, as opposed to real world, conditions.

So much so, that the EPA has changed their testing methods and will apply these to 2008 model year cars. These new FMEs will show about a 30% reduction accross the board of existing FMEs, once more real world conditions are used to produce the estimates. Some cars, especially many of the Hybrid vehicles now on the market will see about a 50% reduction in FMEs.

I guess my point is that the current EPA Fuel Mileage Estimates are flawed and not an especially good Benchmark with which to judge your car's range and fuel ecomony...

Happy Motoring!... Jim'99
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Old 12-12-2006, 10:01 AM   #6
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Tre_oh, to answer your original question, the EPA testing is performed on a dynamometer and the roller resistance is used to account for aerodynamics and the vehicle's weight. The "city" cycle is perfromed with the engine started from cold and the test includes 23 stops with an average speed of about 20 mph over 11 miles and a top speed of 56 mph.

The "highway" cycle is performed with a warmed-up engine, and includes no stops or idling with an average test speed of about 48 mph over 10 miles and a top speed of 60 mph.

Some points to remember is that the manufacturers provide the initial ratings and the EPA only validates about 10-15% of them. Although a guess, I doubt the Boxster is validated due to the relatively small percentage of them sold.

It should also be noted that manufacturer/agency tests calculate fuel consumption by measuring the amount of carbon in the exhaust, not by looking at the fuel gauge like you and I.

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Old 12-21-2006, 11:34 PM   #7
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On my 02 S, I get around 22-25mpg in town, and closer to 28-30mpg on the highway. WAY better than my 01 Prelude. Not steller, but more than reasonable for a sports car IMO.

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