207.5 MPGe

Seven officially received an EPA mileage rating of 207.5 MPGe, based on the official EPA 74 test cycle used for determining mileage for electric and hybrid vehicles like the Chevy Volt and Nissan Leaf, during its recently completed testing at the Chrysler Proving Grounds in Chelsea Michigan.

The testing consists of two parts: coast-down and dyno testing. Coast-down consist of 2 sets of 10 runs up and down a 2.5 mile very straight and level track. The test cars are accelerated above 75 mph then allowed to coast down to 10 mph, during which time speed and distance data is collected via GPS and an on board computer system, in order to collect the following data:

CdA = 5.09
RR = 9.35

Road Load Coefficient A: 12.18
Road Load Coefficient B: 0.0853*
Road Load Coefficient C: 0.00976

Road Load Coefficients represent the drag that causes a car to slow down and are plugged into the equation:

Drag = A + Bx + Cx²

Where:

x = vehicles speed in miles per hour
A = vehicle static drag and is a constant
B = mechanical drag and varies linearly the vehicle speed
C = aero drag and it varies with the square of speed.

Vehicle Weight = 2900 lbs
Vehicle Test Weight = 3149 lbs (249 lbs of test equipment was added during the coast down runs)

*note, this number is higher than it would have normally tested, giving us a penalty in efficiency. This is because the coast down test is normally run by taking the vehicle out of gear and allowing it to coast down once the vehicle has gotten above 75 mph, however Seven had to be run with the transmission in gear giving us the additional drag of our motor, but we knew going into the testing that we’d have to accept that loss because after all the work we had to do this past winter to fix and improve Seven we didn’t have time to build another shift linkage. We told the Chrysler techs that we’d just accept the losses. However, on a positive note, it’s still less than half the lowest numbers ever achieved for mechanical drag during coast down testing at Chrysler.

The data collected from the coast down is then plugged into a calibration dyno which ‘matches’ the vehicle data to the dyno which in turn is used on a test cell dyno to complete the EPA 74 test cycle and determine vehicle efficiency.

Four city and four highway cycles are run back-to-back over a three hour period alternating city-highway-city-highway until all cycles are complete. Numerous parameters are monitored and recorded including energy consumption, vehicle speed, ambient temperature, and dozens more, to determine vehicle efficiency, emissions and a host of other operating parameters, many of which do not apply to pure electric vehicles, e.g. gaseous emissions. Once the tests are complete the vehicle is recharged and the energy used for charging is recorded.

The EPA 74 test then requires the final data to be weighted, 55% city and 45% highway, in order to determine an official EPA mileage number. Note the EPA 74 test determines only a single mileage number by weighting the city and highway numbers as noted above, giving Seven a final combined rating of 207.5 MPGe.

Another common unit of measure for electric vehicle efficiency is to use the total Watt Hours used over the drive cycle, although this is not the official rating method adopted by USEPA for the EPA 74 drive cycle it is a useful tool in that it more accurately reflects total energy used during the combined drive cycles because it is not a weighted number, it is the actual amount of energy used per mile over the entire test cycle. When speaking about electric vehicles it is important to know the actual amount of energy used while driving in order to determine at any time the amount of energy left in your vehicles batteries and thereby how much farther you can travel before having to recharge. Seven uses 160.42 Watt-hours/mile.

This proves Seven to be the most efficient, street legal full size sedan in the world.