Why sparks may fly over IndyCar's domed skids

IndyCar’s return to domed skids for the superspeedways will become a hot talking point in May. Bill Pappas, the series VP of Competition, explained the reasoning behind them to Motorsport.com’s David Malsher.

Dallara’s domed skids are set to be added to the DW12 chassis (now officially called IR15 and IR16 since aero kits were introduced last year) at this year’s Indianapolis 500, Texas 600 and Pocono 500. These have not been seen on IndyCars since 2011, the last year of the previous spec chassis, the Dallara IR09.

The idea of these devices, which bulge downward, is to slow down the rotation of the car once it gets into a spin. With a flat undertray, when a car got sideways at superspeedway-type speeds, the air coming in from the side created turbulence and float, increasing the chance of the car launching. With a domed skid, as the air comes in, it speeds up as it gets constricted under the dome. This creates a low pressure area which effectively sucks the car onto the track surface via hugely increased downforce, reducing the chance of lift and rapidly slowing the rate of spin.

Dallara’s technical bulletin from Jan. 25 showed the diagram above, and read as follows:

  • IndyCar mandates for all Superspeedway events (Indianapolis, Texas, Pocono) domed skids and Titanium rub blocks.
  • There are three domed skids along with three Ti rub blocks. No additional fixings or inserts required. Ti rub blocks are etched to help Tech Inspection check their wear.
  • The domed skids have a “tongue and groove” system to help support the leading edge of the skids. The domed skids come with 13.5” x 3” pockets for ballast plates. The highlighted pockets are the only pockets approved to carry ballast. Green pockets = 0.125” thick ballast; Purple pockets = 0.250” thick ballast. The additional pocketing is for lightening purposes only.

This will force an increase in a car’s ride-height, as IndyCar has vowed to be strict about how much of the titanium skid blocks and/or dome has been worn away by the end of an on-track session.

Within 24 hours of receiving the bulletin, Ray Gosselin, Ryan Hunter-Reay’s race engineer at Andretti Autosport told Motorsport.com: “I’d like to see less reactive measures taken to things. We’ve gone down this domed skid road before with the previous generation car. Then we went away from that for three years and had no problem but we have a couple issues at Indy last year, so now we bring them back.”

The raised ride-heights have reportedly caused drivers to suffer instability problems, but Gosselin added that the domed skids could also cause major gray areas and disputes as the cars went through tech inspection.

“I’m worried it will create more issues for everybody,” he said. “Although IndyCar says it’s going to be black and white as far as whether the team touched the dome skid or not, in practice, I’ll be surprised if it’s that way.”

Michael Cannon, race engineer at Dale Coyne Racing, added: “I fear the car’s instability could truly hurt the racing at Indy, right at the time everyone's tuning in to watch the 100th running of the 500. The past four years we’ve seen great racing there and now we're gonna risk a less exciting show? Seems like bad timing.”

A contentious issue then. Further muddying the waters is that the domed skids for IR16 were approved and introduced by a VP of Competition – Will Phillips – no longer at IndyCar.

Motorsport.com asked his replacement, Bill Pappas for the down-low.

DM: If the domed skids were considered unnecessary once IndyCar introduced the original Dallara DW12 in 2012, what’s the purpose behind them being introduced for the aero kit-equipped cars?

BP: After analyzing the incidents from last May [when the cars of Ed Carpenter, Josef Newgarden and Helio Castroneves spun and flipped upside down at Indianapolis Motor Speedway], both manufacturers came to the conclusion that the reintroduction of the domed skids could help in really slowing the rotation of a car as it starts to spin, adding downforce by a considerable amount. So as a car starts to rotate and gets into the wall, it doesn’t start climbing up it and thus letting air under the backside of the car.

It’s been a safety concern, and when the manufacturers went and did their CFD studies and wind tunnel studies, they came up with the values and decided this idea had merit because it would add downforce once the car went beyond a certain yaw angle.

If this was considered a safety improvement on the old car, why wasn’t it built into the DW12 from its first iteration?

It’s one of those things where they needed to come up with a procedure by which they could examine the theory thoroughly. It took time to investigate it and reach the conclusion that yes, this solution helps reduce that problem of lift.

The diagrams are helpful but can you explain better how these domed skids will appear?

If you look underneath and along the car from the front to the back, you get a convex dome that bulges 7mm difference from one edge of the car to the center and from the center back to the other edge. The centerline of the car is where the dome is at its deepest.

And you have titanium ‘rub blocks’ to prevent teams from just lowering the car to wear away the dome and make it more aerodynamic?

Correct, but they are used more as a warning tool for the teams. They can touch those if they wish, but not the wooden portion of the skid.

The total increase in ride-height is how much?

Well, with a 7mm dome plus the 2mm titanium rub block, the height is raised 9mm. So to be on the safe side, the teams have been running the cars 10 or 11mm higher than before. It all depends on setups and learning to utilize your tools to maximize the downforce and minimize the effect of the domed skid in a straight line.

The titanium rub blocks are the last point before you get to the peak of the dome of the skid plate. So I’m assuming the loss of speed caused by the friction of rubbing them down would persuade teams to err on the side of caution and run the cars higher.

Right. There are several reasons why you don’t want to drag the skid. Look for where the car performs best aerodynamically, and I don’t think it’s when you’re trying to drag the bottom of the car off!

How strict are you going to have to be in tech inspection at the end of a 200-lap race?

The ideal is that a car’s underside won’t touch at all. It’s a safety device, so if you start changing the shape of that dome, it’s going to affect the safety of the vehicle in a spin situation, so the idea is not to touch it.

In the old days, there wasn’t a clear understanding of what a domed skid did, and therefore there was a very loose interpretation about contact with the track. So we’re trying to clarify and eliminate those gray areas, to determine if a team is intentionally trying to rub the thing down to get the car running lower, or whether, for example, a driver changed lanes at Texas Motor Speedway and all of a sudden discovered the car was bottoming out because there were bumps he hadn’t previously had to deal with.

So that’s what we need to decide: where a line will be drawn to determine whether a team has tried to circumvent the intention of the rule or not.

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About this article
Series IndyCar
Event Indy 500
Track Indianapolis Motor Speedway
Article type Analysis
Tags bill pappas, domed skids, lift-off, pocono, precaution, safety, stability, superspeedways, texas