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Detroit — It is a wonder anyone can figure it all out.

A new kind of Indy car on the tricky, long Raceway on Belle Isle would have made things interesting enough at the Detroit Grand Prix this year, especially with them sliding around on the concrete sectors, where the asphalt portions of the track suddenly yield to the brighter-colored stuff.

The squirrels of the state park have some tricks of their own, too, “playing chicken” with cars whizzing by.

But, from the looks of the forecasts for the week, everyone is factoring in Michigan weather, too.

Setting up critical strategies, especially for the use of tires, at the IndyCar series races today and Sunday are judgments fraught with uncertainty.

More: Krupa: Inner drive helps Will Power find his groove

On a hot and humid Friday, with sun in-and-out of clouds, IndyCar officials had to cut track action short, because of lightning in the area, with the scattered showers moving through.

Forecasts called for a cooling off today, a 10-to-15-degree temperature drop for the first race day. But plenty of sun, and far less humidity.

The second race day, Sunday, brings a forecast of a good chance of rain, with sun in and out of clouds. The biggest possibility of rain is forecast for just before the green flag drops at 3:50 p.m.

One thing for certain: Whoever has the best tires strategy might well win each race.

“There’s definitely a right lap to do things,” said Larry Foyt, the grandson of the great driver and team owner A.J. Foyt, who is the crew chief for the Brazilian rookie Matheus Leist and the president of A.J. Foyt Enterprises.

“It can really make a difference.”

CLOSE

John Niyo and Gregg Krupa preview the 2018 Detroit Grand Prix with IndyCar drivers Ed Carpenter, Will Power and Max Chilton. The Detroit News

Simple strategy

For the weekend, each team has 20 sets of tires: nine of primary tires, four of alternate tires and seven rain tires. They are used throughout the weekend, including qualifying

The primary tire is fast and wears long.

The alternate, designated by a red stripe on the sidewall, is faster, with more grip. But it has less longevity.

And the rain tires are a brand-new design, right out of the factory, never been used in competition.

More: IndyCar rookie Jordan King has rocky debut at Belle Isle

Firestone brought them to Detroit for the first time, touting the technology as eventually useful for passenger vehicles.

It could add a critical wild card to the Detroit Grand Prix, especially Sunday.

But even the choice between the two dry tires, with their slick surfaces, is a complex matter, a crucial judgment that can easily make the difference between finishing first and driving with the also-rans.

Both tires must be used in the races, for a minimum of two laps.

“The strategy, itself, is pretty simple,” said Mike Hull, managing director of Chip Ganassi Racing.

“You want to have red tires on the race car when you have (open) track position, when you can take advantage of the speed that’s on the tire.

“When you’re in traffic, and you’re obligated to get a black tire on there, that’s when you put it on,” Hull said

“And then, what you typically do is look for open track position for your next stop.”

But, in Detroit, an additional factor plays havoc with attempts to make the best judgment between the primary and alternate tire.

The extensive amount of concrete on the Raceway on Belle Isle provides less abrasion. So, among the singular characteristics of the idiosyncratic 2.3-mile course is less difference in wear between the primary and the alternate tires than any other road course on the circuit.

Precipitation equation

And then, what if it rains?

“Let me tell you, when the rain comes, it can really be stressful because of a lot of those quick decisions we have to make,” Foyt said.

“Obviously, with the slick tires on a street surface like this, if we get some water, you’re going to want the rain tires, for sure.

“And, especially when it’s wet going to dry, the guy who can get the dries on just at the right time can really, in one lap, get a 10-second gain on someone who stays out.”

The teams have deltas they strategize entering races, the variations in pace that suddenly tell them they simply stayed with the dry tires, or wet tires, too long.

“If we know there’s going to be some weather in the area, we’ll kind of have a lap time delta that we know if it drops to this, we’re probably going to go ahead and go to rain tires, because there’s that much struggle,” Foyt said.

More: Hinchcliffe looking for strong Belle Isle showing after missing Indy 500

Meanwhile, drivers can sometimes adjust their path around the course by mere inches in search of a dryer groove.

“Obviously, we really rely on feedback from the drivers,” Foyt said.

When the switches from wets to dries and dries to wets are properly executed, it can result in a winning driver leapfrogging much of the field.

The new wet tires have deep treads running in asymmetric and direct patterns. Firestone intends eventually to put the new pattern on tires for street vehicles.

“This is going to allow for maximum grip,” said Cara Adams, chief engineer for Bridgestone Americas Motorsport.

“We started development early last year, based on feedback. It’s a very new, innovative rain pattern.”

None of the 23 drivers in the field, already contending with a new model of IndyCar cars and the tough track on Belle Isle, have ever driven the new wet tires.

Chalk it up as just another big challenge for some of the finest racers in the world.

This is interesting racing.

It could get really interesting if it rains.

gregg.krupa@detroitnews.com

twitter.com/greggkrupa

DETROIT GRAND PRIX

When: Friday-Sunday

Where: Belle Isle

IndyCar: Dual IndyCar races on Saturday and Sunday, 3:30 p.m.; each day, 70 laps each

Tickets: DetroitGP.com

WEEKEND HIGHLIGHTS

Saturday

8:45 a.m. — Trans Am Series Race 1

10:05 a.m. — Super Truck Series Race 1

10:55 a.m. — IndyCar Series qualifying for Race 1

12:30 p.m. — IMSA SportsCar Championship

12:45 p.m. — IndyCar drivers’ autograph session

3:30 p.m. — IndyCar Series Race 1

5:45 p.m. — IndyCar Series post-race ceremonies

Sunday

10:45 a.m. — IndyCar Series qualifying for Race 2

11:45 a.m. — Trans Am Series Race 2

2:05 p.m. — Super Truck Series Race 2

3:30 p.m. — IndyCar Series Race 2

5:45 p.m. — IndyCar Series post-race ceremonies

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