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Michelin Detroit Notebook

Michelin’s pre-event Detroit notebook ahead of Chevrolet Sports Car Classic…

Photo: Jake Galstad/IMSA

Same Circuit Plus 24 Months

The Chevrolet Sports Car Classic on the temporary circuit on Belle Isle is one of the pair (Long Beach) of 100-minute events on the IMSA WeatherTech Championship schedule.

Since neither event was held in 2020, this will be the first IMSA street race since Detroit on June 1, 2019, more than 24 months ago.

One recent and very happy announcement is that the paddock and IMSA grid walk will be open to the fans.

While the 2.3-mile circuit remains the same, the track surface may provide a few fresh bumps courtesy of two full years of Midwest winter-spring freeze and thaw cycles.

New Start Time

In recent years, the IMSA race has typically run at noontime on Saturday, in part to help facilitate overnight travel to the Le Mans test day for several IMSA drivers. The IMSA race was then followed by the first IndyCar race of the weekend.

That Saturday schedule is reversed in 2021, as the IMSA race will start at 5:10 p.m. ET and run to 6:50 p.m. The start time is just one hour after the finish of the first IndyCar race of the weekend.

Michelin has asked if IMSA and Detroit race officials plan to sweep the circuit of “marbles” between the IndyCar and IMSA races.

Evolution and Compatibility

The first IMSA practice session on Friday morning will likely offer dusty, low grip levels as the circuit sees its first race cars in more than 24 months. With relatively cooler morning temperatures, some teams may use the early part of the Friday morning session to scuff tires rather than chase chassis set-ups until the circuit grip level is more clearly established.

Between temperature changes and increased track activity, Michelin engineers expect the temporary circuit to evolve from the first practice on Friday morning through the second practice and qualifying that afternoon and then into the early evening race on Saturday.

In addition to temperature changes, IndyCar and Indy Lights teams which each use different tire makes and compounds are expected to log roughly 2,000 laps between the Saturday morning IMSA warm up at 10:15-10:35 and the 5:10 pm IMSA race start.

How the various tire compounds will interact is essentially an unknown heading into the weekend.

Tire Strategies

Tire allocations for the weekend reflect the shorter race duration. Friday’s schedule provides a 90-minute long first practice on Friday morning and an 85-minute second afternoon session with qualifying later that afternoon, nearly a full 60 minutes more than at many events.

The DPi and GTLM entries are each allotted nine sets of tires, with the GTD teams allocated five sets of the Michelin Pilot Sport GT S9M tires.

For GTD entries, the question will be when to use fresh tires. Teams must start the race on qualifying tires and generally plan on having a new set of tires for the mid-race pit stop.

That leaves three sets of tires for nearly three hours of practice, plus the Saturday warm up. Some teams may look to keep a lightly used set of tires available for a late race caution period.

The GTLM Corvettes can take full advantage of their proprietary Michelin options and even mix and match sets using different compounds on different wheel positions if they so choose.

In DPi, teams will likely hold back two fresh sets of tires for pit stops, with a new or lightly used third set in reserve.

Race Strategies

The key to 100-minute street races is often track position. Teams try to avoid being stuck in a train of cars. If they are, they may try to save fuel to stay on track for an extra lap or two (overcut) when the leaders pit or go off-strategy by pitting early (undercut) to emerge on a clear section of track.

Pit stops are critical to gaining or maintaining track position and any caution periods can dramatically impact strategies.


The DPi cars have a maximum fuel window of 35 to 40 minutes, almost certainly a two-stop race. The GTLM and GTD class fuel window is 55 to 65 minutes, making it possible to complete the race with just one mid-race pitstop.

Minimum drive time for the DPi and GTLM entries is just five minutes. For the GTD class, minimum drive time is 30 minutes. That gives teams a wide range of options in planning, and improvising race strategies, including tire strategies.

With a current forecast for temperatures in the low to mid-80-degree range Fahrenheit, conditions are not expected to be ideal for new records, but the level of competition in the WeatherTech Championship and the performance seen at prior events suggests that record are still possible.

Track Records

Here are the current Detroit records:

DPi / Juan Pablo Montoya / 1:19.373 / 106.5 mph / May 31, 2019
GTD / Bryan Sellers / 1:28.942 / 95.1 mph / June 1, 2018

DPi / Felipe Nasr / 1:20.923 / 104.5 mph / June 1, 2019
GTD / Bernd Schneider / 1:29.023 / 95.0 mph / June 2, 2018

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