AERODYNAMICS

Aerodynamics has always been a mystery science. Racecars have to travel over a surface an through the air. The relationship the tires have with the track surface and how well the shape of the racecar deals with the air flowing around it are the two major factors that determine the success of any racecar design.

When a car is going as fast as it will go, all the available engine power is being used to overcome rolling and aerodynamic resistance.

Rolling resistance, which is all resistance to motion other than aerodynamic drag, is usually estimated at only about 15% of engine output. At any speed less than the top speed, there is excess power available for acceleration. Improvements to rolling resistance pale in comparison with the benefits in performance gleaned from aerodynamic improvements. Thus, in XCar, much of your modifications should be spent on reducing aerodynamic drag and increasing downforce. Drag reduction causes an immediate increase in top speed, leaving more power available for acceleration at lower speeds. More downforce increases braking, acceleration and cornering performance. Both of these factors are automatically calculated and displayed on the Car Modification screen.

WINGS
The fin that juts up from the back truck of the racecar is called the wing. Wings provide additional force down on the tires, allowing the tires to produce better grip. The larger the wing, and the more angled the wing, the greater the downforce.

TIP: Although wings create a lot of drag and hurt top speeds, the resulting downforce decreases lap times from better braking, acceleration and cornering performance.

TIP: Jeff Braun, a full-time engineer who makes a living chasing the elusive quick lap, suggests the following rule-For every 10 horsepower increase, crank the wing up another 2 degrees. You'd go the same speed down the straight-aways, but lap times will get better.

Note that wings are devices that operate efficiently within a small range of speed. A wing that's good at 220 mph won't do much at 40 mph.

TIP: On speedways like Red Rock and Infinity Loop, you want to have smaller wings that are angled less since you rarely go below a certain high speed. On road courses like Seattle, and Mid-Ohio, you want to have bigger wings that are angled more since the car has to produce cornering grip at speeds of 40 to 200 mph.