less rolling resistance and will need smaller lighter brakes and other suspension components. This is the virtuous circle when designing lightweight vehicles. Rolling resistance Rolling resistance can be minimized by using the right tires, inflated to the right pressure, correctly aligned, and by minimizing the weight of the vehicle. Performance equation The design of a solar car is governed by the following work equation: which can be usefully simplified to the performance equation for long-distance races, and values seen in practice. Briefly, the left-hand side represents the energy input into the car (batteries and power from the sun) and the right-hand side is the energy needed to drive the car along the race route (overcoming rolling resistance, aerodynamic drag, going uphill and accelerating). Everything in this equation can be estimated except v. The parameters include: Note 1 For the WSC the average panel power can be approximated as (7/9)×nominal power. Solving the long form of the equation for velocity results in a large equation (approximately 100 terms). Using the power equation as the arbiter, vehicle designers can compare various car designs and evaluate the comparative performance over a given route. Combined with CAE and systems modeling, the power equation can be a useful tool in solar car design. Race route considerations The directional orientation of a solar car race route affects the apparent position of the sun in the sky during a race day, which in turn affects the energy input to the vehicle. In a south-to-north race route alignment, for example, the sun would rise over the driver's right shoulder and finish over the left (due to the east-west apparent motion of the sun). In an east-west race route alignment, the sun would rise behind the vehicle, and appear to move in the direction of the vehicle's movement, setting in the front of the car. A hybrid route alignment includes significant sections of south-north and east-west routes together. This is significant to designers, who seek to maximize energy input to a panel of solar cells (often called an "array" of cells) by designing the array to point directly toward the sun for as long as possible during the race day. Thus, a south-north race car designer might increase the car's total energy input by using solar cells on the sides of the vehicle where the sun will strike them (or by creating a convex array coaxial with the vehicle's