How 2018 floor drives IndyCar underbody downforce increase

Changes to the floor on IndyCar's high-downforce 2018 bodywork highlight how the series is reshaping its aero identity.

At the onset of the 2018 project, the Verizon IndyCar Series stated a clear goal to lower its reliance on big front and rear road/street/short oval wing arrays to make the Dallara DW12 chassis perform. In concert with its move toward fewer topside wings, the series also expressed its desire to have the DW12's underwing play a greater role in making downforce.

Together, by lowering the amount of downforce and turbulence created by the exposed topside wings, and letting the floor do more of the downforce work, it will be easier for cars to follow closely and attempt more passes.

IndyCar and its partners at Dallara completed the relatively straightforward process of modifying the DW12's high-downforce wing package, but achieving its goal with the floor wasn't as simple. A comprehensive redesign of the front section that meets the air was required.

Looking at a timeline of how IndyCar and Dallara have used the DW12's floor to make or shed downforce, the original car was delivered with a wide, full floor that filled most of the void behind the front tires. At the floor's leading edge, the design had a modest radius that curled out to the edge where an anti-intrusion fin – the "sponsor blocker" as some team owners dubbed it – was located (below).

Although the section of the underwing between the fin and radiator inlet wasn't overly effective at helping to generate downforce underneath the car (below, in green), it was left unaltered.

That changed in 2015 when Chevy and Honda were allowed to manufacture custom aero kits. Having seen the initial high-downforce numbers produced by the aero kits, which easily surpassed anything the stock Dallara bodywork generated, IndyCar decided it needed to bring those numbers down. Together with Dallara, a new spec floor was introduced in 2015 with the aero kits that took underbody downforce away through new, permanent triangular cutouts (below, in green) that reduced the size of the floor.

The original floor's radius at the leading edge was replaced by a straight piece that provided stability for the anti-intrusion fin, and altogether, the series managed to remove a modest amount of downforce while increasing turbulence.

Rather than lock itself into another situation with a permanent hole built into the floor, IndyCar was determined to give itself options for 2018. The result is a dual-purpose front floor design with a reprofiled hole that could be left open for low-downforce superspeedways (below) or easily converted to make downforce by installing carbon fiber panels that plug the openings (bottom). The unloved anti-intrusion fin was removed altogether.

Despite the intensive work to redesign the forward floor, the series found the same issue it had experienced with the original DW12 floor – ineffective airflow and downforce production in the outer region behind the front tires – had returned, and would need to be addressed.

An innovative solution – a forward floor diffuser, to re-energize the air traveling under the outer section – was devised to rectify the problem. By using a small diffuser with a Gurney flap attached just aft of the floor's leading edge, the stagnating air beneath the floor's outer section is pulled up and through a rectangular slot, and with the Gurney keeping the rising air attached to the upswept diffuser profile before exiting atop the floor, low pressure is created.

"Without the slot, the underwing was too wide and low, so the air did not want to flow well and choked," IndyCar aero director Tino Belli told RACER.

With the permanent holes added in 2015, some of that choking problem was alleviated, but the floor also lost approximately 140 pounds of downforce. With the new diffuser, IndyCar has taken back the 140 pounds of downforce it surrendered and added 140 more for 2018.

"With the slot and Gurney we have created a new front diffuser, which is where the extra 140 pounds of downforce comes from," Belli said.

The placement of the forward floor diffuser in 2018's high-downforce trim also helps the overall aerodynamic balance of the DW12. It's a big improvement over the current hole in the floor that takes downforce away from the front of the car – and shifts the center of pressure rearward – in a detrimental manner on high-downforce tracks.

"We lost a lot of front downforce when we opened up the hole in the floor," Belli said of the 2015-2017 design.

Thanks to 2018's forward floor diffuser, teams should be able to use lower front wing angles at high-downforce tracks due to the center of pressure shift toward the nose of the DW12.

"And it is nice front downforce," Belli added. "We're reducing the reliance on the front wing, which should be good when following another car. Now you'll be able to get closer before the underwing gets affected by the wake of the car in front."