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Chapter 5: Chassis and Design 99During ConversionAs you remove the internal combustion engine parts, it’s likely you’ll discover additionalparts that you hadn’t seen or thought of taking out before. Parts snuggled up againstthe firewall or mounted low on the fenders are sometimes nearly invisible in a crowdedand/or dirty engine compartment. Get rid of all unnecessary weight, but do exerciselogic and common sense in your weight-reduction quest. Substituting a lighter-weightcosmetic body part is a great idea; drilling holes in a load-bearing structural framemember is not.After ConversionBreak your nasty internal combustion engine vehicle habits. Toss out all extras that youmight have continued to carry, including spare tire and tools.After all your work, give yourself a pat on the back. You’ve probably removed from400 to 800 lbs. or more from a freshly cleaned-up former internal combustion enginevehicle chassis that’s soon to become a lean and mean EV machine. The reason for allyour work is simple—weight affects every aspect of an EV’s performance: acceleration,climbing, speed, and range.Weight and AccelerationLet’s see exactly how weight affects acceleration. When Sir Issac Newton was bonkedon the head with an apple, he was allegedly pondering one of the basic relationships ofnature—his Second Law: F 5 Ma; or force (F) equals mass (M) times acceleration (a).For EV purposes, it can be rewritten asF a5 C iWawhere F ais acceleration force in pounds, W is vehicle mass in pounds, a is accelerationin mph/second, and C iis a units conversion factor that also accounts for the addedinertia of the vehicle’s rotating parts. The force required to get the vehicle going variesdirectly with the vehicle’s weight; twice the weight means twice as much force isrequired.C i, the mass factor that represents the inertia of the vehicle’s rotating masses (wheels,drivetrain, flywheel, clutch, motor armature, and other rotating parts), is given byC i5 I 1 0.04 1 0.0025(N c) 2where N crepresents the combined ratio of the transmission and final drive. The massfactor depends upon the gear in which you are operating. For internal combustionengine vehicles, the mass factor is typically: high gear 5 1.1; 3rd gear 5 1.2; 2nd gear 51.5; and 1st gear 5 2.4. For EVs, where a portion of the drivetrain and weight hastypically been removed or lightened, it is typically 1.06 to 1.2.Table 5-1 shows the acceleration force F a, for three different values of C i,for tendifferent values of acceleration a, and for a vehicle weight of 1,000 lbs. The factor a is theacceleration expressed in ft/sec 2 , rather than in mph/second 5 21.95 5 32.2 3(3600/5280)—used only in the formula (because acceleration expressed in mph/secondis a much more convenient and familiar figure to work with). Notice that an accelerationof 10 mph/sec, an amount that takes you from zero to 60 mph in 6 seconds nominallyrequires extra force of 500 lbs.; 5 mph/sec, moving from zero to 50 mph in 10 seconds,requires 250 pounds.