Interlagos - a Formula One set-up guide 16 Oct 2009
Interlagos is a circuit of contrasting extremes, combining slow hairpins with one of the longest straights of the season. Sitting in a natural bowl, it undulates throughout its 4.309-kilometre length, and is notorious for its bumpy surface - although this has improved with resurfacing in recent years. The physical demands of the bumpy circuit are intensified by the fact that it runs anti-clockwise, subjecting the drivers' necks to the opposite loadings experienced at a normal clockwise track.
It's a circuit where overtaking is possible, particularly on the entry to Turn One, and the set-up compromise therefore tends to favour straight-line speed over optimum lap time, to ensure the drivers can make up positions, and defend them, during the 71-lap race. Renault explain how they plan to set-up the R29
The contrasting nature of the Interlagos circuit makes very different demands on the cars. The first and last sectors are made up primarily of long straights, where good top speed is necessary to maintain competitiveness and protect position; this means a low level of downforce is required. However, the middle sector requires the opposite - high downforce to ensure good grip under acceleration, braking and cornering through the twisting series of hairpins. Balancing these requirements gives an optimum downforce setting for achieving the fastest possible lap- time. However, this optimum is then skewed by the demands of racing with other cars. To do so successfully requires competitive end of straight speeds - and achieving these may drag us away from our optimum downforce to a slightly lower setting which allows the drivers to overtake and defend their position into Turn One.
As Fernando Alonso explains: "It's very important to get a clean exit and carry good speed through the final corner so you don't come under pressure down the long straight, which is also uphill. The end of the main straight is the best opportunity for overtaking and if you can get in the slipstream you have a good chance to get by at the first chicane."
The combination of high and low-speed corners means it is hard to find a suitable mechanical compromise at Interlagos. Just as with our choice of aero level, we prioritise certain sectors of the circuit over others. The most important corner at Interlagos is Turn 12, as it determines your speed along the uphill main straight - a full throttle period lasting over 15 seconds. We therefore pay special attention ensuring the car gets a good exit from this corner, even though this can generate some slow-speed understeer in the middle sector. However, any losses incurred with this understeer are outweighed by the benefits in lap-time and competitiveness achieved in Sector Three. The second important factor for the mechanical set-up is the track surface. This was traditionally very bumpy, but the recent resurfacing allows the teams to run lower ride heights. The circuit is relatively easy on the brakes, with just three major braking events, and overall braking energy similar to somewhere like Barcelona.
Alonso explains: "The section from Turns Six to Eight is a difficult part of the lap and shows the contrasting nature of Interlagos. You have to treat turns six and seven as one long corner, but it's important to take a very smooth approach and stay off the curbs. It's also bumpy which can unsettle the car and you have to be careful not to oversteer. Then after a high-speed corner, you have turn eight, one of the slowest on the circuit. This time you have to be aggressive with the steering and use the curbs as well as fighting understeer."
Interlagos includes relatively few high-speed corners with high lateral loadings on the tyres. Coupled with a track surface that is not particularly abrasive, this means we can use relatively soft tyres. Consequently, Bridgestone has made available the medium and super-soft compounds from its 2009 range for this weekend.
The long main straight at Interlagos means engine power is a critical factor at this circuit, and the longest single period at full throttle is over 15 seconds. All the engines, though, must contend with the effects of running at altitude, as the circuit is situated around 800m above sea level. The reduced atmospheric pressure costs the engines around seven percent of their power output; as a result, the 62 percent of the lap spent at full throttle is equivalent to 56 percent at sea level. While this reduces the demands on some components such as the pistons, other parts of the engine, such as the crankshaft, are still subjected to significant loadings. Driveability is also an important factor, especially through the winding middle sector. The drivers run in the lowest gears at this point on the circuit, with sudden changes of direction and significant brake and throttle inputs. Smooth power delivery can make a real and significant contribution to maintaining a stable balance, and optimum driving lines, in this part of the circuit.