IMSA teams preparing for this weekend’s Chevrolet Sports Car Classic held on the streets of Detroit’s Belle Isle are in for one of the bigger technical challenges on the WeatherTech SportsCar Championship calendar.
According to renowned race engineer Jeff Braun, who looks after CORE autosport’s No. 54 Nissan Onroak DPi, Belle Isle is on a literal and figurative island compared to April’s stop on the streets of Long Beach.
“Most people would think, ‘OK, we’ve got two street circuits on the schedule, and Long Beach, Detroit, they’ve just kind of got to be pretty similar. We’ll take the same [chassis] setup to both tracks,” he said. “And, actually, they couldn’t be further from each other. They share a few things — walls at the exit of corners and things like that — but Detroit, it’s a faster, more open, more flowing street circuit.
“I remember the [Adelaide] Formula 1 race was in a park area. Well, Detroit’s the similar kind of thing. Yeah, it’s a street circuit, but it’s more like an actual natural terrain circuit; but then, what makes it completely different than that is, it is bumpier than all get out. The promoters spent money a few years ago to grind down some of the bumps on the left straightaway, which made it decent. You could at least navigate the track, but still, it is extremely bumpy.”
Engineers like Braun will use more of a road course mindset while tuning their cars for Saturday’s 1h40m race than a traditional street course approach.
“So you have this super-fast flowing kind of street circuit, with some twisty bits, but there’s some really fast flat-out fourth gear, middle of fifth gear kind of corners that, you think you’re at a Mosport or something, and then there’s these super tight 90-degree right-handers with huge braking bumps going into them,” he said.
“So it takes a completely different setup than what you would use at Long Beach. Aerodynamics becomes more important than Long Beach, because there are some super-fast corners. The other thing about Detroit is the track.”
A lack of grip is the one Belle Isle attribute that meets street course expectations.
“At Long Beach, the promoters have done a tremendous job over the last three or four years of really preparing the track and making it not so slippery,” Braun said. “They sweep it and sweep it and sweep it. As weird as it seems, at Long Beach, they actually run the drift cars the week before, and that actually puts some rubber down in a couple of the corners that are really important. So Long Beach starts as much more race-ready track and you can start making changes to your car in the first session.
“IMSA, unfortunately, is the first session out at Detroit, and it’s not as clean and it’s not as rubbered-down and stuff, so we’re going to be slipping and sliding for the first 35, 45 minutes before we can really change much and make any progress. A different animal than Long Beach in a lot of ways.”
Digging through CORE’s chassis setup sheets, Braun found one that stood out for its similarities in ride control needs that could be partially applied to Detroit.
“Well, you’d actually take more of a Sebring setup to Detroit than you would a Long Beach setup,” he said. “Sebring, obviously, super, super bumpy, bumps in a different way, and when we go to our seven-post shaker rigs, or when we’re just tuning dampers or building dampers for specific tracks, we consider the actual type of bumps. There’s the braking bumps that go across the racetrack and hit both tires equally.
“Sebring has what I call staggered bumps, where you can go straight down a straightway, but the right front might hit a bump, and the left front might be in a dip, or the concrete blocks are staggered in height. That’s a completely different bump and a completely different setup in engineering answer to deal with those than the ones we deal with at Detroit.”
The use of different curbing styles at Belle Isle poses yet another setup challenge.
“The curbs at Detroit, some of them are concrete, and poured concrete,” Braun continued. “Some of them are actually metal-fabricated curbs that they bolt down, like the right-hander at the end of the back straightaway where you go into the stadium section, so you can hit the curbs differently. So, what we do is super compromised. If the track was smooth, you’d like it stiff, low, because there’s fast corners where you need the aerodynamic downforce, but you’d skip [the underside of the chassis] off the bottom of the skid all the time if you did that. So big compromise, but you have to balance both of those, knowing that there’s a lot of grip in just getting over the bumps well.”
As is the case so often in IndyCar, Braun expects the winners and losers at Detroit to be separated by the quality of their damper programs.
“People who have really had a really good seven-post program, have their dampers dialed in, are going to have an advantage, because that allows them to compromise better where they can be stiff and have the platforms to build anything they need for the aero platform, yet still get over the bumps well,” Braun said.
“So it’s probably one of the biggest engineering challenges of the year, because you can go to Watkins Glen where it’s smooth and fast, and the compromise is not near as great as it is here.”