19/10/2006
NEWS STORY
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 km length, and is notorious for its bumpy surface – although this was improved by resurfacing in 2004. 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 as at a normal track. It is a circuit where overtaking is possible, particularly on the entry to turn 1, and the set-up compromise therefore tends to favour straightline speed over optimum lap-time, to ensure the drivers can make up
positions, and defend them, during the 71-lap race.
Chassis
Aerodynamics: The contrasting nature of the Interlagos circuit makes very different demands on the R26. The first and last sectors are made up primarily of long straights, where good top speeds are necessary to maintain competitiveness and protect position; this means low level of downforce are 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 us an optimum downforce setting for achieving the fastest possible lap-time. At this point, though, we must also consider the demands of racing
around other cars, rather than just in isolation. In order to do so successfully, we need competitive speeds at the end of the long main straight – 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 1.
Mechanical Set-up: 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 priorities 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 3. The second important factor for the mechanical set-up is the track surface. Traditionally considered very bumpy, it used to force the teams to compromise their ideal ride heights. However, the resurfacing in 2004 improved this situation and now means that we can run our optimum ride heights.
Tyres: 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. These can be vulnerable to graining in colder-than-expected conditions, while rear tyres temperatures are also carefully monitored. The numerous traction events, and particularly the propensity of the inside rear tyre to spin in the slow corners, can lead to problems if they are not kept under check.
Weather conditions: The Brazilian GP weekend is often affected by rain at some point, and when it rains, it pours at Interlagos… Michelin's wet weather tyres have demonstrated excellent competitiveness in recent races, but wet conditions at Interlagos carry their own dangers. Most notably, the cambers and undulations of the circuit can lead to rivers down the hill between turns 1 and 2, across the track at turn 3 and on the main straight after turn 12. These unpredictable conditions can turn the race into a lottery.
Engine
Performance: The long main straight at Interlagos means engine power is a critical factor at this circuit. All the engines, though, must contend with the effects of running at altitude, as the circuit is situation around 800m above sea level. The reduced atmospheric pressure costs the engines around 7% of their power output; as a result, the 67% of the lap spent at full throttle is equivalent to 62% 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. Furthermore, both Renault drivers will benefit from new engines at this race. These units will only have to complete a single race cycle, rather than two weekends, and the performance potential of the engines will be allocated accordingly.
Driveability: Just as the contrasting mix of straights and slow corners has consequences for the chassis set-up, it also puts the emphasis on particular engine characteristics. A driveable engine is particularly important in the middle sector of the lap, through turns 8/9/10, as the drivers are running in the lowest gears, with sudden changes of direction and throttle and brake inputs. Smooth power delivery allows them to take the optimum line, without disrupting the balance of the car. The same characteristics bring their rewards in wet conditions as well.