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Chapter 5: Chassis and Design 119and you’re probably using 50 percent (or less) of your drivetrain’s designed capability.So less wear and tear on the gears means you can use a lighter viscosity lubricant andrecover the additional benefit of further increased efficiency.Design Your EVThis is step two. Look at your big picture first. Before you buy, build, or convert, decidewhat the main mission of your EV will be: a high-speed dragster to quietly blow awayunsuspecting opponents at a stoplight; a long-range flyer to be a winning candidate atElectric Auto Association meetings; or a utility commuter vehicle to take you to work orgrocery shopping, with capabilities midway between the former two. Your EV’s weightis of primary importance to any design, but high acceleration off the line will dictateone type of design approach and gear ratios, while a long-range design will push youin a different direction. If it’s a utility commuter EV you seek, then you’ll want topreserve a little of both while optimizing your chassis flexibility toward either highwaycommuting or neighborhood hauling and pickup needs. In this section, you’ll learnhow to match your motor-drivetrain combination to the body style you’ve selected bygoing through the following steps:• Learn when to use horsepower, torque, or current units, and why• Look at a calculation overview• Determine the required torque needs of your selected vehicle’s chassis• Determine the available capabilities of your selected electric motor anddrivetrain torque.The design process described here can be infinitely adapted to any EV you want tobuy, build, or convert.Horsepower, Torque, and CurrentLet’s start with some basic formulas. Earlier in the chapter, equation 2 casuallyintroduced you to the fact that1 Horsepower (hp) 5 550 ft-lb/secThis was then conveniently bundled into equation 51 Horsepower (hp) 5 FV/375where V is speed expressed in mph and F in lb force.Horsepower is a rate of doing work. It takes 1 hp to raise 550 lbs. one foot in onesecond. But the second equation, which relates force and speed, brings horsepower toyou in more familiar terms. It takes 1 hp to move 37.5 lbs. at 10 mph. Great, but you canalso move 50 lbs. at 7.5 mph with 1 hp. The first instance might describe the forcerequired to push a vehicle forward on a level slope; the second describes the forcerequired to push this same vehicle up an incline. Horsepower is equal to force timesspeed, but you need to specify the force and speed you are talking about. For example,since we already know that 146.19 lbs. is the total drag force on the 3,800-pound Rangerpickup at 50 mph, and equation 5 relates the actual power required at a vehicle’s wheelsas a function of its speed and the required tractive force: