Renault's guide to Interlagos set-up 20 Sep 2005
Fernando Alonsos race engineers, Rod Nelson (chassis) and Remi Taffin (engine) explain the technical requirements for achieving a fast lap around Interlagos, setting for Sunday's Brazilian Grand Prix.
Rod Nelson: Brazil is a circuit containing opposing characteristics: two sectors of the track include long straights which require good top speed, while the second sector is a tight and twisting succession of long corners which ideally requires higher downforce levels and good mechanical grip. In terms of downforce levels, the optimum one-lap setting is often higher than the levels we actually race at. This is because the only regular overtaking point on the circuit is into Turn 1, and we need good straightline speed to achieve this - so we end up moving away from optimum downforce to obtain the most raceable set-up possible. Drivers who favour one-lap speed will often end up rueing their decision for 71 laps on Sunday.
In terms of how we balance the car, the combination of high and low speed corners also makes it difficult to find the right mechanical compromise. The most important corner for lap-time is Turn 12, because this conditions your exit speed on the long uphill straight. We therefore set the car up to be quick exiting this corner, which can in fact result in too much slow speed understeer in the second sector and we often have to dial out understeer in turns 8, 9 and 10 through the weekend. However, the compromise favours this solution because the lap-time gained in Sector 3, and the ability to defend your position properly, outweighs the losses in the slower corners.
Historically, we have tended to consider Brazil as a very bumpy circuit, particularly through Turn 3 leading onto the back straight. Last years resurfacing has improved the situation on this front though, which allows us to run ride heights where we want to; any increase, particularly at the front, inevitably compromises mechanical and aerodynamic performance.
Tyres at this circuit are generally quite soft, as there are few high speed corners. If temperatures are lower than expected, this can lead to front tyre graining (as we saw last year with Fernando Alonso), and the numerous traction events mean that rear tyre temperatures need to be kept under control, particular on the left rear which is susceptible to wheelspin, as most of the corners are left-handers and this corner of the car is therefore more lightly loaded.
The weather can always be a factor in Brazil, particularly because we never encounter light rain: if it rains, it pours With a number of cambered corners, and a new surface, you tend to get rivers between turns 1 and 2 down the hill, across the track at Turn 3 (as we saw in 2003) and after Turn 12 on the start-finish straight.
Finally, Interlagos sits at 800 metres above sea level - the highest of any circuit in the season. The lower atmospheric pressure means the engines are around seven percent down on power, and the wings generate about seven percent less downforce and drag. Of course, this problem is not unique to us, and is the same for all our competitors.
Remi Taffin: Interlagos is situated at the highest altitude of the year, some 800m above sea level. This brings with it reduced atmospheric pressure, and power output is therefore around seven percent lower than we could expect in normal atmospheric conditions. As such, Interlagos becomes - for certain parts of the engine - a relatively easy circuit. For example, at a given engine speed, the pistons are subjected to nearly ten percent less loading than in normal conditions. Indeed, the cars are at full throttle for 58 percent of the lap, but the effort this involves is equivalent to approximately 54 percent full throttle at sea level. However, the circuit still includes high speeds, and one very long straight, so while it may be less demanding for certain engine components, others such as the crankshaft - will still be working hard.
As with any circuit which has strongly contrasting demands in terms of downforce, a powerful engine is a major asset - and the RS25 fits this description. Greater engine power will allow the chassis engineers to run more wing while achieving the same end-of-straight speed, and this additional downforce will in turn speed up the car through the twisting infield. Furthermore, the engines driveability is extremely important. Turns 8/9/10 see the drivers regularly using the lowest gears, and a driveable engine with smooth power delivery will help them place the car accurately and also disrupt the chassis balance less as they are changing direction and in the transition from braking to acceleration. The driveability of the RS25 is appreciated by the drivers, and should be an asset through this twisting sequence of corners.