Tricky compromise on Indy set up

When you combine the unique characteristics of the American circuit with the 2003-style regulations, set-ups become a difficult thing to get right. Allan McNish, Renault F1 Team's test driver, explains.

The track on which this weekend's US Grand Prix is held is the product of two completely different philosophies in circuit design: a never-ending straight of 1.7km makes up one half, a twisty infield portion which resembles Budapest, the other. The challenge the engineers face is easily summarised: you need the best possible maximum speed down the straight, and the highest level of downforce in the tight corners. The problem? Grip calls for downforce. which is the main obstacle to achieving good top speed.

"That means that the best set-up is always some form of a compromise," explains Allan McNish. "Up until last year, there was a well-established strategy. On Saturday, the key was to put on a good amount of downforce because the way to get the best lap time is to maximise grip in the twisty section, even if you lose out a little in straightline speed. For Sunday, we would then take off some wing in order that you didn't get overtaken down the straight."

From now on, though, it will be impossible to employ this strategy. The rules state that the cars must go into parc fermé on Saturday, and leave on Sunday morning, with any set-up changes prohibited. "That makes our life much harder," continues Allan. "Before deciding on a set-up, we will have to get a rough idea of the strengths and weaknesses of our competitors so that we can decide how to weight our own set-up compromise."

"What's more, we will qualify having already decided on our strategy. If things don't go as expected, though, we will still be able to play with a number of parameters during the race to improve things: downforce levels on the front wing, differential settings, brake balance."

One other major factor must be taken into account when setting up the R23: tyres. "They generally work better with lots of downforce," explains Allan. "The extra load brings grip, which stops the car sliding and damaging the tyres. But at Indy, too much downforce means you are slow down the straight. and you will get overtaken. I think we will see plenty of passing on Sunday. Friday qualifying has already shown that the difference in top speeds between the different cars is quite high, so we will need to find the right balance between downforce and tyre behaviour."

And then, we will still have to wait and see if the rain comes to complicate matters further. "That will be a deciding factor," concludes Allan. "Typically, grip levels at Indy improve significantly between Friday to Sunday. If it rains, the rubber will be washed off the circuit and the track surface will be as green as on Friday. That will make it harder to generate mechanical grip, which might in turn have an influence on the choices we make with the aerodynamics. It's always complicated!"

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