One of Portimao's most distinctive characteristics is the frequent elevation change, with the circuit rising and falling dramatically throughout the course of the lap like a rollercoaster.
These gradient changes are far steeper than they appear on TV, but although they don't pose a technical challenge to the cars themselves, they have a much bigger impact for the drivers.
Elevation change does not impact the performance of the car as much as you might expect. It does put a little more strain through the cars, but they are built to handle heavy kerb strikes and large forces anyway, so a bit of extra compression in the suspension is no bother for modern-day F1 machines.
But different types of elevation change impact the cars in different ways, depending on the circuit and the topography.
Some will require tweaks to be made to the car set-up, to really dial the car into the track characteristics and maximise them, while others will require the right compromise to be found.
Take Spa-Francorchamps as one example. The intense downhill and uphill complex of Eau Rouge requires teams to increase the front ride height of the car. This is to handle the vertical compression forces of around 3g that the car is experiencing, as it is pushed into the ground through the sudden downhill-to-uphill change while at almost vMax (maximum velocity, otherwise known as top speed).
The vertical compression of the tyres and suspension through this section of track is one of the highest on the calendar, which isn't particularly surprising considering Spa has the biggest difference in elevation change (102 metres between the highest and lowest point) in F1.
Yet this level of compression isn't a consideration at a track like Portimao, because while there are some steep slopes, the elevation changes aren't taken at such high speeds. The elevation change from lowest to highest point is also not as dramatic as a track like Spa, with a difference of just under 30 metres, but the ups and downs are more frequent.
However, these undulations do still have an influence on how the car handles and reacts during a lap. First, at Portimao there are uphill and downhill corner entries and exits, so a mix of gradient directions. You can't set the car up for one or the other, because that'll compromise too many of the other elements, so a middle ground has to be found to ensure the car reacts well enough in all of those scenarios.
Second, an interesting factor in Portimao are those downhill corner exits. The loads of the car go 'light' on exits such as Turn 11, which has a 16-metre drop, the steepest decline in gradient at the track, and the car effectively just wants to go straight on. It doesn't because of gravity and downforce, but the drivers still feel a noticeable lack of grip and this can make the car more unstable. It also makes traction trickier, so there is a delay with the drivers getting the power down.
Another track with some obvious elevation change is the Red Bull Ring in Austria. The cars don't experience compression or the 'light' feeling here, but there is track 'warp' to contend with. This is where there are different gradients on the track left to right, as you go along, effectively creating a spiral effect.
Turn 3 in Austria is a clear example of this, because the corner creates a crest - from the uphill entry and downhill exit. As drivers navigate this warp, the car tends to want one wheel (the inside front on this occasion) to get some air and this upsets the car balance.
As for the drivers...
Looking specifically at Portimao, the elevation change has a much bigger impact on the drivers than it does the cars. The undulations create some blind corner apexes, including Turns 8, 11 and 13. This makes it tougher for them to see the entries to the corners and create reference points for braking and turning in.
Because of this, it can make it more difficult to learn the track and build up speed during those initial laps in practice. This is certainly something Mercedes found last year, on its first visit to Portimao, where it took a little longer during practice for the drivers to settle in and know where they need to commit to their racing lines and braking points.
Arguably the trickiest complex for the drivers is Turn 10 and 11, because it is a double-right hander with a blind entry - as the track rises by roughly 12 metres - and a steep downhill drop on the exit of 16 metres. The steeper the slope, the more an F1 car wants to become airborne. But it doesn't due to gravity and downforce.
However, the load under the tyres (called the contact patch) reduces as a result and this impacts the grip the driver has on the exit. So, it does make the car a bit more unpredictable at these points on tracks like Portimao, where there is a dramatic drop in gradient.
The unsighted entry to the Turn 10/11 sequence and track width means we see plenty of different approaches by the drivers - particularly during practice, where they are finding the limit. Even with the blind entry though, over time and with experience, they know exactly where to point the car.
The elevation changes do put a little bit more force through the driver's body and make things more physically demanding during a lap. While this isn't too severe an issue in Portimao, owing to the speed the drivers tackle the crests and troughs, at a circuit like Spa-Francorchamps, this is a different story.
The sweep through the Eau Rouge, for example, is a massive compression. Just as it puts more forces through the car and its components, additional forces are also being experienced by the driver too. Thankfully for the drivers, where elevation is concerned, these are short, sharp bursts of additional force rather than more sustained forces experienced through cornering.
The undulating nature of some tracks has a small but important impact on the racing itself. For example, in Portimao the elevation changes and unsighted entries to certain corners create more than one line, which can create opportunities for overtaking or mistakes. But it can also make the racing line even more defined, depending on the local topography.
Safety and visibility are further factors for the drivers to consider, as there are several sections that are unsighted. The dip before the first corner is one such example at Portimao, as is the drop after Turn 8, where you cannot see what is ahead until you peek over the crest. These are all further challenges and thought processes being added to the drivers' workload during the sessions.
The blind corner entries also increase the risk of mistakes in Qualifying as the drivers are picking braking or turn-in points without the normal track reference points that they'd have in clear sight. So, it is tougher to be precise, particularly when on the limit during Qualifying at a track like Portimao.