EXPLAINED: What makes Spa-Francorchamps a tough track in terms of power units

Due to the combination of never-ending straights, high-speed corners and a slow chicane, it is vital to "optimise the available energy and fuel," claims Roel Sourbron, who works as ICE engineer at Ferrari.

Spa-Francorchamps is one of the most spectacular tracks, very popular with teams and drivers because of its technical complexity and the challenges it presents.

It is the longest track on the calendar, exceeding the seven kilometre mark by four metres. Its three sectors have very different characteristics: the first is the quickest and includes what are probably the most famous corners, Eau-Rouge and Raidillon.

Following the combination of Eau-Rouge and Raidillon, driver complete a long straight, followed by a heavy braking area. The second sector is more twisty, featuring a mix of medium-speed corners, several of them downhill, whilst the third sector is more flowing with a slight but nevertheless noticeable incline.

The Spa-Francorchamps track is one of the most demanding for the power unit. Asked what can be done to optimise the power unit's performance at Spa, Roel Sourbron, who works as ICE engineer at Ferrari, said: "At 7.004km the track is the longest the cars have to cover during the season. From a power unit point of view, the most important feature of the track is the two long “straights” from turn 1 to turn 6.

"Because the famous corners Eau Rouge and Raidillon are taken at full throttle, the drivers are asking the power unit to deliver its full potential for 23 seconds.

"That is 1.8km without lifting! This long stretch starts after the slowest corner on the track and it is therefore important to optimise the power unit potential from low speed, all the way through the gears to the car’s top speed.

"To complete the picture, from Eau Rouge the track goes steeply uphill, with a gradient of up to 14%. The corner and the hill stress the power unit so much that the car actually slows down despite delivering more than 900HP. The second long “straight” also contains a very high speed corner, Blanchimont, that is taken at full throttle.

"This time, the drivers do not lift for 20 seconds while covering 1.6km. These fast sections are connected by a combination of very high speed corners and a slow chicane. This makes it very important to optimise the available energy and fuel for the long straights without compromising in between.

"Due to the lap length, fuel consumption is high but the climbs and descents make the lap time sensitive to weight. Therefore, care must be taken to estimate the exact fuel consumption and carry the right amount of fuel, in order to be as light as possible."

Sourbron was born and raised in Belgium, close to the Zolder race track where F1 last raced in 1984 and only about one hour away from Spa-Francorchamps.

The Ardennes circuit is famous for temperature fluctuations and sudden changes in the weather. Asked how these two factors affect the power unit, Sourbron noted: "At Spa, you need to expect the unexpected. Rain and cold temperatures are as likely to happen as sunny and hot conditions.

"The track is especially demanding for the combustion engine in sunny and dry conditions due to the PU operating at its full potential, requiring maximum performance.

"However, in cold and damp conditions, the engine’s internal components are stressed in a quite different way, being prone to longer periods of extremely high combustion pressures.

"Due to the location of the circuit – whose highest point is 461 meters above sea level and features a total elevation change of over 100 meters – fluctuations in atmospheric pressure can also place additional demands on the turbo.

"As in Austria and even more so in Mexico, low barometric pressure requires the turbo speed to increase, testing the components to the limit of their design.

"Finally, if it rains, the track completely changes character. Rather than pure power unit performance, drivability and energy deployment become crucial.

"The high-speed corners, Eau Rouge and Blanchimont, are not taken at full load anymore and throttle pick-up needs to be smooth to guarantee drivability in slippery conditions," Sourbron concluded.