Brooklyn II: Tony Stewart preview

It's a numbers game at Michigan. ATLANTA (Aug. 14, 2002) - If you're a math phobic, Sunday's Pepsi 400 at Michigan International Speedway may not be the race for you. Talk of downforce counts, drag coefficients and valance heights are joined ...

It's a numbers game at Michigan.

ATLANTA (Aug. 14, 2002) - If you're a math phobic, Sunday's Pepsi 400 at Michigan International Speedway may not be the race for you. Talk of downforce counts, drag coefficients and valance heights are joined by discussion of points standings, average finishing positions and lap times.

"Math, not racing, takes center stage at Michigan. So pay attention, especially you there in the back."

For instance, the Pontiac camp received a half-inch kickout to the front valance on the nose of their race cars. That means the leading edge of the Pontiac's front air dam must not extend more than one-and-a-half inches forward of the bumper. The rule change should give the Pontiac teams more front downforce, a term used to describe the amount of wind pressure on an object. "Counts" are the measuring increments used to determine how little or how much downforce actually exists.

"I hope you're writing all of this down, because there will be a test."

You'll also hear teams talk of drag coefficients, and how slippery their race car is through the wind. With Michigan being a fast two-mile oval, a good drag coefficient is key. The smaller the drag number you have, the better your car is aerodynamically. The drag coefficient is a number that aerodynamicists use to model all of the complex tendencies of drag on shape, inclination and flow conditions. The equation is simply a rearrangement of the drag equation where we solve for the drag coefficient in terms of variables. The drag coefficient (Cd) is equal to the drag (D) divided by the quantity: density (r) times half the velocity (V) squared times the reference area (A).

"Simple enough, right? Okay, moving on"

Points. It's really what NASCAR Winston Cup Series racing is all about. Finish the season with the most points, and the big trophy and $3 million check are yours. Heading into Michigan, the points race is extremely tight, with just 106 points separating the top-five, while 14 races remain on the schedule.

Tony Stewart, driver of the #20 Home Depot Pontiac, vaulted himself from seventh to fourth in points, 104 behind series leader Sterling Marlin, following a dominant win last Sunday at Watkins Glen (N.Y.). With an average race finish of 14th in the 22 events he has run thus far, Stewart has scored 52 more points this season than he did last year at this time. A strong run at Michigan, a track where Stewart won in June of 2000, would only add to his point tally and aspirations of a championship.

"Now break out your number two pencils you have 400 miles to complete the test."

We've been hearing all year of drivers complaining of an "aero push" while racing in traffic. What is an aero push?

"You have two types of balance on your race car. You have mechanical balance and aero balance. Your mechanical balance is comprised of springs, shocks, sway bars and suspension pieces. Your aero balance relates to the total aerodynamics of the car - how the air flows over the top of the race car and how it creates downforce in different areas.

"If you're running with a car right in front of you, you don't have the air hitting the front of your car as you would if you were running in clean air, where there's no one in front of you. When someone is in front of you and you're not getting that air pushing down on the front of the nose, the car isn't getting the downforce it needs to stick to the race track. That creates an understeer condition, which makes the car push out toward the wall. That's what's happening when you hear drivers complain of an aero push."

You received another half-inch kickout to the front valance of your Pontiac per a NASCAR rule change heading into Michigan. Will it help the aero issues Pontiac teams are facing and did the initial half-inch kickout you were granted back in June make much difference?

"Not much. Not the little bit that we've seen so far performance-wise. But it should get The Home Depot Pontiac closer to where it needs to be. We're not quite there, but we're racers, so I don't think we're ever satisfied with where we are at the current moment. I know the team took the car to the wind tunnel on Tuesday, so we have an idea as to how much of a help it'll be, but I don't think you ever really know until you get out on the race track. What I feel in the race car might be different from what the wind tunnel has told us. At the end of the day on Saturday, after those two practice sessions where we'll have had the chance to do some drafting, we'll know a lot more." Is it overall downforce where the Pontiac is deficient or is it specific to either the nose or the decklid?

"It's just overall. You go in the corner and it's tight, and you get on the gas and try and come off of the corner and it's loose. That's just total downforce, because The Home Depot Pontiac is typically really good without any changes. So it wasn't a bad set of tires. The tires have been pretty consistent all year. The only thing that's left is downforce. You hate to gripe about it, but all of these teams are spending a lot of money going to wind tunnels. They're not just out there watching the wind blow around them. They're making their cars better and better, and it's making the aero side of this business more important."

Track position and pit strategy seem to be the two biggest variables at Michigan. When and how do you make the decision to sacrifice tires for track position, or depending on the circumstances, track position for tires?

"I think it just depends on how your car is working. If your car is driving well, one that keeps you up toward the front all day because it's fast, then just two tires can keep you pretty quick. In that situation, you could make a big gain at the end by just taking on two tires and maintaining your track position. Even some guys who are behind and don't have their car the way they want, by taking on two tires, the track position they gain helps out more than four tires would. But when you get right down to it, I think Michigan is a track where if your car's good, then it doesn't matter whether you take two tires or four."

Because of the aerodynamic disadvantage you're dealing with, how much harder has this team had to work to overcome the aero issues associated with the Pontiac?

"We definitely have to work every bit as hard as everybody else does. The good thing is that we're not trying to reinvent the wheel. We're just trying to take what we've got and find a little bit here and a little bit there to keep making our Home Depot Pontiac better than what it already is. If we're able to do that, it'll keep us toward the front all day. If we're not able to do that, we're going to struggle."

Michigan is a track where a driver can search for different grooves, as opposed to Indianapolis or New Hampshire, where there is really only one true groove. As a driver, do you appreciate that more?

"It's nice knowing that as a driver you can help yourself out and you're not relying so much on the car. Regardless of what everyone else is doing, you can find a way to help yourself out. It makes you feel good knowing that because the place is so wide, you can move around, and basically, earn your money that day."

At what point do you start to move around on the race track to find a better handle for your race car?

"As soon as you feel like you're not where you need to be. If you feel like you're slower than the pace you need to be running, you're going to move up the race track and find a place that helps balance your race car. Really, from the drop of the green flag, you do it from there on out."

How big a role does drafting play at Michigan?

"It's big since Michigan is such a momentum track. You can work the draft pretty well, and if there are some guys racing up in front of you, it'll help you catch up to them. It's a place where you really have to watch and pay attention to the draft."

Do certain makes of cars, or more specifically, do certain team cars affect your car differently in relation to aerodynamics?

"Sometimes it does. It depends on what little things are done by each team to their car's bodies. Sometimes it makes it more difficult. Sometimes it makes it easier. You just have to go out there and run with guys during practice and find out which cars makes your car draft better."


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About this article
Series NASCAR Cup
Drivers Tony Stewart , Sterling Marlin