In an effort to improve the oval-racing product, the Indy Racing League, sanctioning body for the IndyCar Series, will loosen up some of the aerodynamic rules that it had previously tightened in the name of cost-savings and parity. The problem with tightening the engineering rules in oval racing is that the large teams still spend just as much as they would have before, but now they spend it on the minutiae rather than on more substantial engineering. For the Meijer Indy 300 at the Kentucky Speedway on August 1st, team engineers will be allowed some latitude in areas they’ve not been allowed to experiment in a long time. The three major changes will be the allowance of rear-wheel ramps, wheel-end fill caps, and sidepod extensions. Lets take a look at each of these areas in turn and examine how they’ll affect the performance of the car and the quality of the racing.
Rear Wheel Ramps
Carbon fiber deflectors in front of the rear tires direct air flow up and over the tire creating more downforce both directly and indirectly by funneling more air over the rear wing. These devices will also reduce drag induced by the air becoming turbulent as it passes around the sides of the tire rather than over. This is a relatively inexpensive piece to fabricate, but the real expense is in the development. You’ll see a lot of effort put into developing the right shape for these ramps, and expect teams to be extremely protective of their designs. This does mean more wind tunnel time and/or some simulated wind tunnel time using CFD (computational fluid dynamics). The reduction of drag will lengthen the pit window for many teams, but it will also mean the potential of extending the tires beyond their effective distance, especially with the additional downforce wearing on them even more.
Around half of the aerodynamic drag on an IndyCar is attributable to the wheels. Hanging out in the air stream, the wheels act like egg beaters creating extremely turbulent air in their wake and producing copious amounts of drag. In the late 80’s, teams attempted to combat this with solid caps on the outside of the wheels to minimize the generated turbulence and drag. Using a smooth brake backer plate on the inside of the wheel also aids in reducing drag. Keeping the air on the inside of the wheel laminar is even more important than the air on the outside since the air that passes on the inside of the wheel, as it moves downstream, will pass over other elements of the car such as the sidepod, rear wheel ramps, radiators, and eventually the rear wing. The less laminar and the more turbulent the air is over these elements, the less effective they are at producing downforce, or cooling in the case of airflow over the radiators. The drawback to using wheel fills either on the outside of the rim or as a backer plate is the reduction of air flow over the brake rotors and calipers. On an oval circuit, this isn’t a significant issue since brakes are seldom used except when pitting. On a road or street circuit, however, keeping the brakes cool is critical. Don’t expect to see these elements at Sonoma or Mid-Ohio, but you will see various applications at Kentucky.
The sidepod extenders are designed to further reduce drag while increasing downforce on the car by maintaining laminar flow as much as possible over the rear of the car behind the sidepods and directing air flow smoothly to the rear wheel ramps and rear wing. The current sidepods truncate several inches in front of the rear wheel and suspension assembly. Extenders will cover this gap. The rear wheel ramps and brake backer plates are both relatively straight forward, not to say that development of these pieces isn’t important. The sidepod extenders, however, are fertile ground for the engineers to apply their craft and really show off their talent. Yes, wind tunnels and CFD analysis will be helpful, but engineering talent will be the true difference maker.