PRUETT: Tech overview of Chevy's IndyCar aero kit

After years of secrecy, Verizon IndyCar Series fans have finally gotten a look at an aero kit. And what was your first reaction when you saw Chevy’s road course bodywork? Excitement? Disappointment? A blend of both? I’ll admit to being underwhelmed when I saw the renderings.

I’d heard whispers of info over the last few months, and all signs pointed to an Indy car with DTM-style dressing from nose to tail. It’s possible my enthusiasm for the stylish, wind-contorting DTM cars led me astray because, well, I’m an optimist.

It’s also possible my hopes were set impossibly high. The Dallara DW12 owns a special place in the pantheon of ugly racecars and, in retrospect, it was unrealistic to expect Chevy (or Honda) to cure the DW12’s aesthetic shortcomings on their own with little more than bolt-on body panels.

If you’re wondering why the “Chevy Aero Kit RC/SO” (road course/short oval) package looks so similar to the stock DW12 (center at left, with two views of Chevy's kit), it’s due to the aero kit regulations rather than a lack of creativity from the Bowtie. The car’s fundamental shape could have been changed if aero kit designers were allowed to make serious revisions to the sidepods, but the regulations require the original radiator ducting and mounting location to be retained. With this area excluded – the biggest section of bodywork on the car, the base DW12 was always going to overshadow the first-generation aero kits.

Next pages: Additional images and analysis of the Chevrolet aero kit

Starting at the front of the car, significant changes have been made to the front wing assembly, but if you look closely, there’s has a hint of the “Chevy” front wing package they developed for the Dallara IR07 that raced through 2011 (BELOW RIGHT).

The DW12’s thick, heavy front endplates (at left, ABOVE) are gone, and the upper “double decker” wing element has also been deleted. A return to a more traditional front wing array has been made with the DW12 main element and two new, smaller, cascading elements on each side. The RC/SO endplate is also a significant departure from the stock Dallara piece.

The slab-sided DW12 endplate was capped with a flat piece of carbon fiber that partially blocked oncoming air from hitting the front tires. With Chevy’s design, a multi-dimensional approach has been taken to ramp air up and over and out and around the tire. The use of a contoured Gurney flap on the outer edge of the endplate is designed to extract air from the front wing package.

Chevy has also added tall stalks to the outer portion of the front wing with small wing elements sitting high in the airstream. The DW12’s front endplates served another purpose as drivers routinely made side-to-side contact with them (or nerfed a car from behind) without any major consequences.

Minus the tall, sturdy DW12 front endplates, it’s easy to see the Chevy’s front wings being driven over and debris littering the track when similar contact takes place. It makes you wonder if the decision to move the RC/SO front wing adjusters to the middle of the elements was done to reduce the likelihood of that metal device being trampled and thrown into oncoming traffic.

Per the rules, the RC/SO uses the stock Dallara front wing main element, and when the SW (speedway) kits arrive, we’ll see brand-new main elements designed by Chevy and Honda.

Aero kit rules prohibit changes to the nose, shock cover, and the Dallara tub, which moves us back to the floor and sidepods on the RC/SO as the next area to explore. IndyCar’s new spec floor comes from Dallara with cutouts in front of the sidepods on both sides of the cockpit to reduce downforce.

Late changes by IndyCar to the road course/short oval aero kit also required the removal of the floor sidewalls (that are located on the inside of the rear wheels), and the removal of the strakes that mount to the diffuser.

Combined, all three changes to the 2014 road course/short oval floor specification is said to cut nearly 1000 pounds of downforce from the cars in 2015 trim.

Viewed from overhead, the DW12 (left, ABOVE) had a triangular shape starting from the back of both sidepods to a point in front of the cockpit. With Chevy’s RC/SO, the triangle is still there, but a few new contours have been added. A slight return to the “Coke bottle” waist that became popular on many Formula 1 and Indy cars during the 1980s and ’90s has returned.

Air hitting the front of the DW12 sidepods was routed along the car and out or over the rear tires, but with the RC/SO’s slightly taller sidepods, Chevy has broken the DW12’s uninterrupted sidepod design to route air between the drivetrain and rear wheels via the “Coke bottle.”

The RC/SO sidepods feature pronounced bulges that house forward-swept exhausts and turbos in a tight package reminiscent of Honda’s compact turbo/exhaust system last year. Moving around those bulges, the sidepods taper inward as air is diverted in a number of directions. The large DW12 rear tire humps have been replaced with an interesting compromise.

Chevy uses a giant ramp to send air over the rear tires, but it also uses a bubble that’s approximately the same width as the tire’s contact patch to reduce turbulence and drag while routing that air to the rear bumpers. Below the ramp, Chevy makes use of a wedge – similar to units seen on early Indy Racing League designs – that blocks air from hitting the face of the rear tires, and diverts air inside and outside the tire. A small dive plane is also used on the lower, outer portion of the wedge.

Looking at the widest part of the sidepod, Chevy has added a tall, rectangular flow conditioner that is reminiscent of those seen in F1 during portions of the 2000s. Below the flow conditioners on the floor, Chevy has added an extension to the stock Dallara fin that serves as an anti-wheel interlocking device. The extension is used to keep air concentrated and flowing around the sidepod, rather than letting it dump out into the airstream and create a wider, draggier wake.

A final, subtle tweak has been made to the floor directly behind the extension where Chevy has raised and contoured a panel the raises and accelerates the air flowing between it and the dive plane.

An obvious holdover from the DW12 is the overhead air intake for the turbos. Chevy has managed to create a narrower, more tapered engine cover that drops away at the bulkhead. The triangular vent at the back of the DW12 engine cover – which was used by Honda during its single-turbo era – is gone, giving the RC/SO a clean, uniform look.

At the back of Chevy’s kit, the most notable changes include the switch from a single upper rear wing element with a giant chord, to two adjustable elements with shorter, more familiar chords. F1- and Champ Car-style vented rear wing endplates are hard to miss, and help to lower pressure on the top side of the wing while improving the vortices that trail behind the car. The RC/SO rear wing endplates are huge, and remind me of the less ornate plates that began appearing on mid-’80s Indy cars (ABOVE RIGHT).

The boxy DW12 rear “Karsdashian” road course bumpers have grown in every direction, and borrow some of their profile from the taller speedway versions that were seen through 2014. The RC/SO bumpers are long, tall, and have secondary flow conditioners added to the topside with small Gurneys in place.

Altogether, Chevy says more than 100 parts comprise the RC/SO, and with performance as its sole purpose, a notable decrease in lap times should cause IndyCar Series track records to fall. Chevy and Honda have been busy testing their new road course aero kits since last October, and while it’s clear that performance levels have been raised, one unsavory handling characteristic has been amplified.

As you might recall from coverage surrounding the DW12’s on-track introduction, the overweight chassis and engine combination placed too much weight bias on the rear of the car. Drivers complained about a built-in understeer in slower corners, and eventually, a few modifications were made to bring the weight distribution forward enough to make the understeer manageable. Teams also turned up the front downforce to move the aero weight distribution forward, and while it wasn’t necessarily optimal, it was an effective workaround.

The DW12 bodywork lacked winglets, dive planes, ramps other downforce-adding items from the cockpit back, making the understeer issue one to solve through mechanical means. With the new aero kits – and this is also true for Honda – drivers have more front downforce at their disposal, yet compared to the smooth DW12, more weight has been piled onto the rear through the extra RC/SO pieces.

The size of the new rear bumpers is a perfect example of aero kit components that are bigger, heavier and, in their case, hang over the rear axle, which exacerbates the understeer problem. It’s far from perfect, but both manufacturers are facing the same issue.

Referring back to IndyCar’s move to strip downforce from beneath the car, the move was made in the name of safety. Although the holes in the floor were set in motion long before aero kit testing began, the new maximum road course downforce levels pushed beyond some of the limits the DW12 chassis components were designed to withstand. Whether it was running the risk of buckling the suspension or other load-bearing items, IndyCar had to find ways to remove a significant amount of downforce from the 2015-spec cars in a uniform manner.

The DW12, in perfect conditions, made somewhere between 4900 and 5400 pounds of maximum downforce in road course trim (the numbers vary – most quote 5000 pounds). Even with the new cut-out floor (that took away approximately 300 pounds of downforce) in place, it’s believed road course downforce jumped to a maximum in the neighborhood of 6300 pounds. Keep in mind that doesn’t include the base weight of the car, driver, or fuel. Add those in and you’re looking at something slightly north of 8000…

As we know, IndyCar’s answer was to pull the sidewalls and strakes from the floor, which subtracted another 700 or so pounds of downforce. When the cars show up to race this year in high-downforce road course configuration, aero kits are expected to add an extra 500-600 pounds of downforce to what was available in 2014.

The DW12 was already a nightmare to wrangle at tracks like Mid-Ohio, where the lack of power steering makes upper body strength a crucial aspect of getting the most from the car. Take that DW12, strap two 300-pound NFL defenisve lineman the size of J.J. Watt to the car, and you have an idea of the brutal forces drivers will have to overcome when the RC/SO is installed. 

Although IndyCar’s floor changes brought downforce levels down from the danger zone, it also caused another problem as the cars now rely on more dirty, turbulent downforce from the topside of the cars. Using the floor to make big downforce allows reduced wing angle settings, and with a lesser reliance on topside downforce, closer racing is produced as drivers can run close behind a car without losing the handling.

It should make it harder for drivers to follow a car through faster corners, and if that’s the case, the quality of racing could suffer. We’ll get a better sense for the kind of impact aero kits will have on the series when the entire field turns up for Spring Training at Barber Motorsports Park a month from now.

Honda is expected to unveil its kit shortly before the event, and with the track’s rolling landscape, the positives and negatives of introducing aero kits will be on display. Will they move the needle and bring more interest to the series? Will they prove to be expensive engineering projects that make passing unnecessarily hard? Would it have been wiser to ask Chevy and Honda to spend millions of dollars on additional marketing and promotions instead of aero kits? We’ll have those answers – and more – very soon.

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