[SD987]

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.