The engineering challenge of Spa's legendary corner
Eau Rouge at Belgiums Spa-Francorchamps circuit is arguably the most famous corner on the Formula One calendar. Over the years, this complex has presented one of the biggest challenges in the sport, and over those years, the corner has, like the cars, been changed and developed. Renaults Executive Director of Engineering, Pat Symonds, examines the ongoing relationship between car, driver and that celebrated section of tarmac.
When we consider the nature of this (the Eau Rouge) challenge, and how it has evolved over the years, it is interesting to see that just as it seems to be getting easier, a change to the cars can put the ball right back in the teams' court. Indeed, this is what we expect to happen for 2005.
Speeds through the corner increased up until 1998 (peaking at 286 kph/178 mph in 1997), when the introduction of grooved tyres and narrow track cars brought a significant decrease in grip, and hence cornering speeds. From 1998 onwards, we see a steady increase in speeds once more, with a significant jump in 2001 as the tyre competition begun the previous year got into full swing. An equally significant step was made in 2002, when not only did the tyres develop further, but the corners were slightly realigned and also resurfaced, in the interests of safety. This led to the corner being easily flat in qualifying that year, although in the race it still required a small lift of the throttle through the corner. Having said that, even when taken flat, the high lateral accelerations and hence tyre scrub, coupled with the steep rise in elevation, result in the car losing around 20 kph/12 mph from entry to exit of the corners.
From an engineering point of view, the corner is an important one as good speed through here provides an overtaking opportunity at the end of the straight. In order to negotiate the complex quickly, it is important to have the right level of grip, and hence an aerodynamic set-up that does not compromise the high straight-line speeds required (around 320 kph/200 mph). In addition, the drivers need complete confidence in the car through this series of corners, and in order to achieve this it is necessary to have good high speed stability, and maybe even a touch of understeer.
Finding this handling sweet-spot is not just a case of achieving the correct aero balance, as the dramatic elevation changes in the corner have severe effects on the suspension. The left hand part of the corner generates a lot of suspension compression, and the car goes light in the final part. It is necessary to ensure the car does not hit the ground hard in the compression, but also that during this phase, any non-linear behaviour in the suspension, such as the bump rubbers, do not produce a sudden change in handling as the car tries to bottom out. Equally, ride heights can vary by as much as 25 mm/1 inch through the sequence. When choosing set-ups, just a couple of millimetres can make a significant difference to handling, and it is therefore obvious that the car needs aerodynamic characteristics that do not cause large movements in the centre of pressure even when ride heights and pitch angles vary. If these factors are managed correctly, if the driver has the grip he expects, and if the grip and the balance of that grip remain constant through the corner, then the challenge becomes a much easier one.
This year, we expect to negotiate Eau Rouge at approximately 310 kph/193 mph, compared to 286 kph/178 mph in 1997. Furthermore, with the progress in both car and tyre design over the past two seasons, the corner should be taken flat out for much of, and perhaps all, the race. Next year, though, the situation will change once more, as it has done through recent F1 history. Just considering the losses from the aerodynamic changes that we will be accepting for 2005, we can expect the minimum speed through Eau Rouge to drop by over 20 kph/12 mph (to 1997 levels), and indeed the top speed at the end of the straight will be 9 kph/6 mph lower. The drivers will also be lifting off the throttle for around 0.4 seconds, a level similar to that which we saw in 2000. The challenge of taking Eau Rouge flat, superseded by advances in car and tyre design since 2002, will return, and Spa will be all the more a true classic circuit for it.