What We Can Learn Through Four Practices at Indy

Half of the practices drivers will get before the 102nd running of the Indianapolis 500 are now complete. With four practices down, we can start to get a good look at which drivers are looking fast this May as well as which manufacturer has the upper edge around the 2.5 mile oval. 
Marco Andretti has been the most consistently fast driver of the week, finishing in the top five in speed in all four of the practice sessions so far. He is the only driver to do this and also holds the fastest lap recorded so far with a 227.053 mph lap in the third practice session. This lap speed is 0.7 mph faster than the second fastest driver so far, Scott Dixon. 
Andretti’s Honda was the first of what would become two Honda drivers at the top of different practice sessions: A Chevy-powered driver finished in the top spot in the first and second practice sessions, and a Honda-powered driver did the same in the third and fourth sessions. This led me to wonder which manufacturer has had the upper hand so far at Indy. 
For the purposes of this article, I chose to look at top to bottom speed for each manufacturer, meaning I included every driver’s top speed so long as they met the minimum 215 mph lap speed in the given practice session. I could have chosen to look at just the top five or ten drivers for each manufacturer, but in order to gain a holistic view of the field at this year’s 500, I looked at all 35 drivers who will attempt to qualify for the race
In order to see which manufacturer has the upper hand, I found the average top speed for all drivers in all four of the practice sessions so far, separated by manufacturer. Chevy had a total average top speed of 223.323 mph for the four practice sessions and Honda had a total average top speed of 222.775 mph. This is a close gap between the manufacturers, but our analysis isn’t done yet. In order to test whether the gap between the manufacturers is significant, we can use what is called a Two-sample t-test to see what the probability is that the gap we see between Chevy and Honda is just due to random variation and chance. 
Here are the results from that analysis:
As we can see, there is just a 3.33% chance that we would see a gap at least that big between Chevy and Honda if the performance of the two manufacturers was actually equal. This means it’s very likely the gap between Chevy and Honda, taking into account all drivers, is real. Chevy has a slight advantage across the field through four practice sessions. More specifically, since the top speeds of sessions (which we used in our analysis) are almost always set using a tow (following another car in the draft), we can say that Chevy has an advantage when running in a pack over Honda. 
Friday’s practice at the speedway will be used to get teams ready for the qualifying sessions that are scheduled to take place this Saturday and Sunday. This will hopefully give us data on no-tow speeds in qualifying trim and give an idea of what we can expect for qualifying this weekend. For now we can comfortably say that Chevy has the speed over Honda when running with other cars, but that’s not to say that won’t change over the next week as teams perfect setups and get ready for the Indy 500. 

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Photo courtesy of Joe Skibinski/IndyCar

by Drew

Sonoma Raceway Engineering Guide

Scott Dixon rolls through the Turn 9 Chicane during the GoPro Grand Prix of Sonoma at Sonoma Raceway — Photo Credit: John Cote

IndyCar heads to Sonoma for the season finale this weekend with six drivers still eligible for the championship. Let’s take a look at the Engineering Guide for Sonoma Raceway in California.

Surface: Road Course
Distance: 2.385 miles
Laps: 85

Sonoma is IndyCar’s tenth road/street course of the season, and also one of the toughest. The track features very short straights (one is made out of the drag strip located at the circuit), an esses section, and a brake heavy hairpin that leads on to a curvy front stretch. Besides navigating a rolling start with other cars around them on a narrow front straight, drivers also need to be ready for the heavy braking section heading into turn 2. The steep turn coupled with the braking can upset the balance of the car and send drivers running wide in qualifying and at the start of the race. 

The things teams will need to focus on this weekend are downforce through the high speed corners and acceleration rather than top speed. Cars don’t really get a good chance to top out going around this track, but getting up to speed on the slightly longer straights is imperative. Through the esses, maintaining momentum can really help you close up on a car that is struggling through the section. The hairpin like corners of 4 and 6 will provide some good overtaking opportunities in addition to the “classic” hairpin that is turn 11. A poor run out of the final turn will make you a sitting duck to cars behind on the front straight.

Sonoma is unlike almost any of the other road courses this series competes on. It doesn’t have a trademark long straight like we see in Long Beach or St. Petersburg. Therefore, it’s going to require a setup unlike any of the other tracks. Chevy have won six of the nine road/street course races this year, and they seem to have the upper hand heading into Sonoma as well. Their aero kit has been the winner most of the season despite Honda’s recent push in winning two of the last five road course races. 

However, some of the reasons for Honda’s slower pace could be because of higher downforce levels on the stock aero kit setup. Their front wing element has always had downforce in mind, with three flap elements and two endplates holding two more flaps. This has slowed them down on the straights but will benefit them in the turns. Also, if you look at their rear pod (pictured in red below), you can see the curved bottom edge that serves as a diffuser for the car. It sucks the air out from beneath the car, lowering the air pressure and therefore increasing downforce without adding any additional drag. 

Chevy opted for an angle parallel (no curve up) to the ground which makes their diffuser less effective. I don’t know if it will allow them to outrace the Chevy’s and win, but it could certainly help make them more competitive on a track where mid to high speed corners are plenty.

Update: 8/29 – If you have any more questions about the cars or Sonoma Raceway (or IndyCar engineering in general), let me know in the comments below and I’ll do my best to answer!

How Chevy and Honda Reinforced Their Aero Kits

IndyCar mandated that both Chevy and Honda reinforce their aero kits before the Indy Grand Prix of Louisiana this weekend. We got a chance to see these changes first hand during the free practice sessions on Friday. Here’s a look at what each manufacturer did to combat the debris problem we saw in St. Petersburg.

Chevy's reinforced upper element.

Chevy had two main regions to focus on when it came to making their adjustments: the front wing upper endplate and the rear bumper pod. Starting with the upper element, Chevy bulked up the part by adding four bolts and a reinforcement ring to the base of the upper and attaching that to the wing (shown in black with four silver bolts above). This reduces the chance of the upper being broken in the case of car to car contact on the side. This piece was very fragile in St. Pete and was a relatively simple fix.

Chevy's reinforced bumper pod with diagonal bar support.

Next we head to the rear of the car where Chevy has reinforced the bumper pod. They added a bar on the inside of the pod going diagonally from the left front to the right rear. This is highlighted in yellow on the No. 22 car above. The addition of this bar reduces the likelihood of the pod crumpling in or losing its form during contact.


Honda added two pieces to reinforce both sides of their endplate, as well as the bottom.

Honda’s changes to their aero kit were all centered at the front of the car, specifically on the front wing endplate. Honda has added two carbon fiber-esque pieces to the inside and outside of the front wing endplate to strengthen it. This is pictured in Derrick Walker’s hands below. The pieces glue on and add a good amount of structural support to prevent the plate from breaking in the event of contact.

Honda's reinforcement pieces.

The same piece, although slightly wider, has been added on the bottom side of the wing below the endplate, too. This helps support the three flap setup Honda has gone with on their kit, which is quite fragile as we’ve seen. These reinforcement pieces should make the wing that much stronger and make it less likely to break after light contact.

NOLA Motorsports Park is a fairly wide track with lots of run-off area, so we may not see just how beneficial these additions are this weekend. However, when the series heads to Long Beach, another tight street course, next week, we will get a good look at how well the reinforced kits hold up.

IndyCar Mandates Structural Upgrades to Manufacturer’s Bodywork Components

IndyCar announced on Thursday that it has “mandated structural upgrades to strengthen designated Honda and Chevrolet bodywork components” ahead of this weekend’s race at NOLA Motorsports Park, according to a press release.

Photo: Chris Owens

The modifications include the addition of components that will improve the overall strength of the bodywork for both manufacturer entries, Chevrolet and Honda. The components have been redesigned by each manufacturer and approved by IndyCar for implementation.

“We applaud both Honda and Chevrolet for their efforts to implement these changes,” said Derrick Walker, IndyCar President of Competition and Operations. “With a quick turnaround from St. Petersburg, our partners were very diligent in making these enhancements in time for this weekend’s event,” he said.

“We will continue this collaboration and expect additional improvements in the future.”

The upgrades introduced to the aero kits “were implemented to minimize the amount of damage to bodywork components in the event of car-to-car contact.”

“IndyCar delivers a quality racing product and we will always be proactive to implement changes that benefit our fans,” Walker added. 

“These upgrades are a good first step that will make immediate improvements to the race this weekend at NOLA Motorsports Park.”