The reasons why Indy 500 cars are HUGELY different from F1 designs

This week we have two of the most iconic races on the same weekend, the Monaco Grand Prix and the Indy 500. While we know that technological evolution has driven the design of F1 cars over the years, what drives IndyCar design?

DNA of American Motorsports

To understand what drives the design philosophy for Indycars we first need to understand the DNA of American Motorsports. American Motorsports circles around 'spectatorship' and 'racebility' and not around 'technology' as much. They have a bottom-up approach in which the driving question is what kind of racing would our fans enjoy? the answer is quite a simple one, wheel - wheel racing with the potential of surprise winners and why not add a photo finish to that list? To meet that requirement list, the IndyCar series is technically a spec series, wherein to level the field you have Dallara as the sole chassis supplier with Honda and Chevorlet as the engine manufacturers. So this inherently means close competition where the drivers, team management and race car setup make all the difference.

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Indycar Setup Around Ovals

As the ovals are asymmetric w.r.t driving, the car set-up is optimised asymmetrically. When it comes to the mechanical side, the tyre camber, toe, spring rate and damper rates are all set up asymmetrically. The weight distribution is also asymmetric, all the heavy components such as the radiators are setup asymmetrically, so if it’s a left-handed oval then all the heavy bits will be on the left side to assist the centripetal force allowing you to go faster around ovals. However, keep in mind that the cars have to be symmetric externally. IndyCars around ovals also take advantage of specific aerodynamics:

Less Loaded Wings: Wings are not major downforce-producing elements for this event, they are there to balance the car and the major downforce-producing element is the floor. This is because the floor in ground effect is more efficient w.r.t downforce to drag ratio and also wings create wakes which limits racebility. Rear Tyre Faring: This largely eliminates the rear tyre wake hence encouraging closer racing. Engine and Brake Cooling: Cooling requirements are minimalistic because of the large speeds at the Indy500. There is enough mass flow rate to cool the engines and the brakes due to the high speeds. Usually, there are small naca ducts to facilitate the cooling.

Design For Close Wheel - Wheel Racing

Close wheel-to-wheel action at above 300 km/hr results in a high probability of a big crash, but Indycars have inherent design features to avoid this. Max Y Coordinate: The maximum Y coordinate must belong to the Floor, and not to the wheel which prevents the wheels from touching during side-by-side action that normally results in scary accidents. Sidefloor Blocker: A Floor Sidewall blocker was introduced to avoid the interlocking between wheels and underbody Rear Bumper: When drivers try to slipstream, there are chances that their front wheels can touch the rear wheels of the drivers ahead which can lift off their vehicle. IndyCars have rear bumpers in order to avoid any longitudinal wheel-to-wheel contact.

Aerodynamics for Stability and Safety

Next up let's look at how Indycar leverages Aerodynamics to improve stability and safety in order to avoid big crashes 90 deg Yaw cases

Race cars were never studied at 90 deg yaw angle until Dallara decided to do so. One of the big problems at the Indy500 event was if the car was spun 90deg at 300 km/hr. In this condition, the car would flip over quite aggressively. But by studying the Aerodynamics of the car at 90 yaw angle, Dallara was able to minimise the flip-over moment. This was done by producing a high amount of downforce on the floor at 90 deg yaw angle and by creating enough of a high-pressure zone on the lower half of the sidepods to counter the flip-over moment.

Take Off Instability While slipstreaming if the driver misjudged his overtaking and touched wheels coming from behind, the slight nose-up condition created would make the car take off at those speeds. The cutouts you see on the floor are present to avoid exactly that. It reduces the high-pressure zone in the forward floor which facilitates the nose-up moment for that attitude of the car.

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Shubham Sangodkar is a former F1 Aerodynamicist with a Master's in Racing Car Design specialising in F1 Aerodynamics and F1 Data Analysis. He also posts aerodynamics content on his YouTube channel, which can be found here.

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