With Chevrolet not building a true Corvette GT3 contender until 2023, IMSA allowed Corvette Racing to convert its GTLM car to something more resembling a GT3 car in order for the team to compete in this year’s new GTD Pro class in the WeatherTech SportsCar Championship. IMSA presented the team with a list of changes in order to fit in and worked with Corvette Racing to implement them – some obvious GT3 items such as adding ABS and a ballast box to the passenger floor footwell, where all GT3 cars are required to carry extra weight. And while seemingly straightforward, some of the changes are more complex than the seem.
“With [the addition of the ballast box] a lot of the components within the passenger area of the car had to move,” explains Corvette Racing team manager Marc Maurini. “The AC had to move, the fire bottle has had to move, and the chassis has been modified to hold all these components in a new location. It’s been quite a big tear-up in that area to make sure that we get to where we need to be.”
The wing hasn’t changed, but IMSA specified a greater angle of attack for Daytona which hurt straight-line speed; that angle of attack was reduced before the race weekend. Engine power has been limited via restrictor, which grew between the Roar weekend and the Rolex 24 at Daytona. There also had to be some changes within the gearbox.
“What the rules require in GTD Pro is that it’s strictly a limited-slip differential. We were not in compliance with that previously for GTE. The components we had to remove are some additional widgets and gadgets that make it limited-slip, plus,” says Maurini.
The change with the most impact, however, is the tires. In GTLM/GTE, the manufacturer could work with the tire supplier, in this case Michelin, to design a tire to its specifications. In GTD, however, the teams must run a customer tire, with everyone having the same construction and compounds.
“It’s a pretty massive change,” says Maurini. “Corvette tires [in GTLM] were designed with Michelin as a technical partner to work specifically with our car. Now, obviously, moving to a customer tire that everyone has, it’s not designed for us. So a lot of changes have been made on the mechanical side of the car to rebalance for that tire. And the tire is a lower-performance tire, as you’d expect with a customer option.”
It may seem odd that switching tires can have that big an impact – after all, both are Michelins. But different construction can mean different compliance, different effective spring rates and different behavior.
“From a driving point of view, there isn’t a great deal of difference,” says No. 4 Corvette driver Nick Tandy. “And I think the ultimate pace differential isn’t massive. The one thing that we kind of miss from the GTLM and the confidential tire was the free choice that we had. We could design and develop a tire with Michelin that works with our car – same as Porsche did, same as Ferrari did. Where here, we are given a tire and have to make the car work for that tire. This is one of the differences when the car is actually on track, and you’re driving it to the limit of the grip of that tire. There’s less ultimate pace out of that tire, but it’s a very similar sort of feeling.
“But that’s the biggest difference, the fact that we could tune a tire to the car where now we have to tune the car to the tire. So it’s good and bad in some ways, because you have one variable that’s out the window; but you also miss the chance to be smarter than the others and tune that variable to your advantage.”
Corvette Racing made good progress throughout the Roar weekend and through the Rolex 24, although it was likely hampered by the first three practices of the second weekend being marked by less-than-ideal track conditions. In the first practice session for the Roar, both Corvettes were more than 3s off the pace of the fastest GTD Pro cars. By the time the qualifying session for the qualifying race came around, they were 1.5-1.7s off. After some Balance of Performance changes for the Rolex, they were 1.0 to 1.8s slower than the fast cars in the final practice, and in the race the best times for both cars were just over a second off the fastest race lap.
“It’s been running pretty well,” said Tandy mid-race. “We find that when we’re in a pack we’re actually not too bad, because we can really draft off of the cars in front, and then we seem pretty strong in the infield. It just becomes different when we drop off the back of the pack, and then it looks like some of the leaders begin to stretch their legs out a bit.
“We were learning every session because the thing is, we know the car. We know a lot of everything that has to do with how the car operates. We’ve tested with these tires, we’ve tested the ABS system, things like that. What we’re learning here is how everything works together at Daytona with Daytona-specific aero requirements, suspension, geometry settings and tire pressure… stuff that is Daytona-specific.”
Now the team will have to figure out how to do the same for Sebring. Then WeatherTech Raceway Laguna Seca. Then Long Beach… But Daytona’s banking and Sebring’s bumps are outliers in the IMSA WeatherTech SportsCar Championship. Things learned in Monterey are more likely to apply at Mid-Ohio and Watkins Glen.
“I think IMSA has done a really good job,” says Maurini. “We’ve worked pretty closely with them and it made the process pretty streamlined. Certainly we’re outside of the standard ruleset, so we appreciate their effort to get us into the GTD field and allow us to compete. I put the engineering crew on this team up against anyone in the paddock, so I think we’ll get there quickly. I think we’re already very close, but there are certain things you can only learn in a race that we haven’t had a chance to learn yet.”