Quote:
Originally Posted by Mitchell
I know that many things go into the calculations for MPG and l/100km but it is interesting that EPA rates the M3 at 20MPG highway but here we get a spec of 8.5 l/100km with the DCT and 9.3 with the 6 speed on the highway. That is equal to 27.5 US MPG and 25 US MPG. Why the difference of 7.5 MPG and 5 MPG highway between the way the two systems measure?
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didn't you answer your own question? it's the different ways of measuring a test cycle by EPA and the EU counterpart:
Quote:
Originally Posted by mdosu
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In the European Union, passenger vehicles are commonly tested using two drive cycles, and corresponding fuel economies are reported as 'urban' and 'extra-urban', in liters per 100 km and (in the UK) in miles per imperial gallon.
The urban economy is measured using the test cycle known as ECE-15, introduced by the EEC Directive 90/C81/01 in 1999. It simulates a 4,052 m (2.518 mile) urban trip at an average speed of 18.7 km/h (11.6 mph) and at a maximum speed of 50 km/h (31 mph). The extra-urban cycle or EUDC lasts 400 seconds (6 minutes 40 seconds) at an average speed 62.6 km/h (39 mph) and a top speed of 120 km/h (74.6 mph).[24] EU fuel consumption numbers tend to be considerably lower than corresponding US EPA test results for the same vehicle. For example, the 2011 Honda CR-Z with a six-speed manual transmission is rated 6.1/4.4 l/100 km in Europe and 7.6/6.4 l/100 km in the United States
EPA thru 2007:
Two separate fuel economy tests simulate city driving and highway driving: the "city" driving program or Urban Dynamometer Driving Schedule or (UDDS) is defined in 40 C.F.R. 86 App I and consists of starting with a cold engine and making 23 stops over a period of 31 minutes for an average speed of 20 mph (32 km/h) and with a top speed of 56 mph (90 km/h).
The "highway" program or Highway Fuel Economy Driving Schedule (HWFET) is defined in 40 C.F.R. 600 App I and uses a warmed-up engine and makes no stops, averaging 48 mph (77 km/h) with a top speed of 60 mph (97 km/h) over a 10-mile (16 km) distance. The measurements are then adjusted downward by 10% (city) and 22% (highway) to more accurately reflect real-world results. A weight average of city (55%) and highway (45%) fuel economies is used to determine the guzzler tax.[30][31]
2008 and Beyond:
As a means of reflecting real world fuel economy more accurately, the EPA adds three new tests[34] that will combine with the current city and highway cycles to determine fuel economy of new vehicles, beginning with the 2008 model year.[35] A high speed/quick acceleration loops lasts 10 minutes, covers 8 miles (13 km), averages 48 mph (77 km/h) and reaches a top speed of 80 mph (130 km/h). Four stops are included, and brisk acceleration maximizes at a rate of 8.46 mph (13.62 km/h) per second. The engine begins warm and air conditioning is not used. Ambient temperature varies between 68 °F (20 °C) to 86 °F (30 °C). The air conditioning test raises ambient temperatures to 95 °F (35 °C), and the vehicle's climate control system is put to use. Lasting 9.9 minutes, the 3.6-mile (5.8 km) loop averages 22 mph (35 km/h) and maximizes at a rate of 54.8 mph (88.2 km/h). Five stops are included, idling occurs 19 percent of the time and acceleration of 5.1 mph/sec is achieved. Engine temperatures begin warm. Lastly, a cold temperature cycle uses the same parameters as the current city loop, except that ambient temperature is set to 20 °F (−7 °C).
EPA tests for fuel economy do not include electrical load tests beyond climate control, which may account for some of the discrepancy between EPA and real world fuel-efficiency. A 200 W electrical load can produce a 0.4 km/L (0.94 mpg) reduction in efficiency on the FTP 75 cycle test.[36]