How to engineer a Brickyard winner

My notes go back to 1992 when, as a naive ex-Formula 1 engineer, I saw four, apparently geometrically identical, left-hand turns and thought, 'How hard can it be?' I soon realised that turning left at over 220mph with very little downforce isn't easy. And those four corners, they're all different.

The problem with Turn 1 is psychological. As drivers hurtle down the straight, the grandstands seem to encroach upon the track. This makes them turn in too soon; they apex early and then have too much turning left to do on the exit, resulting in excessive understeer, scrubbing off speed or even running out of road.

Turn 2 should be easier. The entry speed is slower owing to that scrubbing off in Turn 1, and the length of the chute between the corners. However, there is a tunnel below the track that has caused a dip, which can destabilise the car on entry. On exit, there is an access gate in the wall, which has also caused a discontinuity in the surface that can unsettle the car.

Turn 3 should be the same as Turn 1, but without the grandstands it's easier to negotiate. However, a series of ripples have formed in the track. These are what limit how low a car can be run around Indy.

With small wings, the majority of the downforce is generated by the underbody, and the lower the car, the greater the downforce. With the track bank angle here the car is at its lowest at the apex of the corners, and not at the end of the straights... or it would be if we could get over those ripples without bottoming. Turn 4 is described as the easiest, a slower entry speed like Turn 2, but without the bumps and ripples.

Andy Brown with Ryan Briscoe during this year's practice © LAT

All four turns also have another unsettling aspect, the effect of the banking on entry. One would think that banking the corners would help. This would be true were the angle the same all around, but at Indy the straights only have three degrees of banking compared to nine degrees in the corners.

As the driver approaches the turn, driving alongside the outer wall, with the angle winding up from three to nine degrees, he feels the effect of driving uphill. Then as he turns in at the top of the banking and drives down towards the apex, it's like going over a humpback bridge.

Trusting the spotters

Spotters are an important part of oval racing, making all the difference by describing if another car is trying to pass. The best spotters can provide invaluable assistance to the engineer by helping the driver take the correct line. The car handles completely differently at Indy depending upon which line the driver takes.

An ideal late turn-in makes for a straighter exit, therefore less speed is scrubbed with the front tyres, the result being more speed down the straights. Turning in too late, the driver will complain of being 'loose' on entry (a problem the engineer may not have to fix if the spotter can get the driver turning in at the correct point).

If the driver does apply a late turn-in, then excessive steering lock is needed to get the car to the apex, and speed can be scrubbed with the front tyres during this phase of the turn. The driver should definitely be taking the right line before attempts are made at tuning the handling.

Gauging the conditions

Temperature variations can be tricky to cope with, but the biggest weather problem is the wind. A tailwind into Turn 1 increases the road speed at which you arrive at the entry point, but effectively reduces airspeed. That means arriving faster but with less downforce. Then at the exit of Turn 1, you have a significant sidewind blowing you into the wall.

Brown worked with Wheldon at Gannasi © LAT

If you thought you had problems with entry oversteer/exit understeer before, then they just get worse. When you arrive at Turn 2 the sidewind is still trying to keep you against the wall, but as you turn into the wind on exit, and as the headwind hits the front wings first, it can 'pin the nose' of the car causing exit oversteer - the exact opposite set of problems to Turn 1.

It's been 21 years since I first went to Indy and I don't think I've got all four turns right yet. The times that we've won, we just got it less wrong than everybody else...

Toe

Stand behind a car set up for Indianapolis and you will notice each wheel leans over at a different angle, and points in a different direction. Because we don't want the rear of the car stepping out, we point both the rear wheels towards the centre of the corner.

The left-rear gets more loaded on entry and less at mid-corner, and the opposite is true of the right-rear. Having different absolute toe settings on each wheel is one of the most valuable tools for combating different handling on entry and at mid-corner.

Ride height

In the pitlane, the left-hand side of the car sits lower to the ground than the right ('tilt'). The car is at its lowest when at mid-corner, when the lateral loads as well as the vertical (banking) loads are also at their highest.

By selecting the static 'tilt' angle to match the amount of body roll in the corners, the underside of the car will then be parallel to the ground when viewed from behind in the turns, and hence it can be run as low as possible without one side or other of the bottom of the car rubbing the ground, and the other side still being 'up in the air'.

Loads

Whereas road-racing engineers try hard to arrange for equal loads on each front tyre so as not to lock up one wheel or the other under braking, at Indy we can set the static load on the right front to be, say, 100lb higher than on the left front, so as to take load off the right-rear tyre and hence extend its life.

Teams need to find the right balance between downforce and drag © LAT

On the other hand, if there is too much understeer, we put more load back onto the right-rear. (The driver can adjust this from the cockpit as well via a slave cylinder under the right-rear spring platform, effectively extending or reducing the length of the right-rear damper.)

If all else fails there are still the cockpit-adjustable front and rear anti-roll bars, plus springs (a different rate on each corner), and tyre pressures to play with.

Aerodynamics

The wings are standard fare. The compromise between downforce and drag is amplified at Indy. The front wings themselves are a good tool for helping mid-corner by adding incidence, but then this is also a good way to get the car to spin.

Andy Brown was talking to Ian Wagstaff