There was a time when F1 teams could be pretty confident that any gains found in their wind tunnels could be bolted on their cars at the next race to make them quicker.
But ever since the ground-effect era returned in 2022, things have been slightly different, as there is no longer a direct link between extra downforce and improved lap time.
In fact, three years into the regulations, as teams approach the upper ceiling of what is possible, it appears there is more uncertainty than ever about the translation of the promise found back at base and it being realised out on track. It's why McLaren has stuck with its Miami floor up until now.
Over the course of this season, there have been repeated tales of upgrades brought to the cars producing some unintended consequences.
This includes Ferrari’s Spanish floor bringing back high-speed bouncing, balance problems triggered by Aston Martin and Red Bull’s upgrades, or uncertainty posed by Mercedes’ Spa floor.
But with the sophistication and knowledge of car development being at such a high level right now compared to previous years, why have teams hit trouble?
There is a two-fold answer to this, which encompasses both the nature of the cars and the difficulties of simulating them in wind tunnels.
As Aston Martin engineering director Luca Furbatto explained: “You need to run very close to the ground, but it's very difficult to test in the wind tunnel.
“Depending on the map you're running, something might look a bit better in the wind tunnel. So you do it, but then maybe you bring it to the track, and then there is a bit of bouncing, you need to lift the car up, and then you lose what you have gained.
“I think quite a few teams have fallen into that trap. So it's not super easy to develop.”
The ride height issue
The current ground-effect cars are far more sensitive to ride height (especially so close to the ground) than the older generation of grand prix machinery.
In fact, one phenomenon of the cars is that as they get closer to the ground, the downforce steadily increases – until they hit a point (or touch the track surface itself) where it is all released.
Teams are therefore walking a tightrope when it comes to finding that tipping point where performance peaks.
As Ferrari performance engineer Jock Clear explains: “In the past the cars would bounce off the ground, off the plank, but the aero was never that critical.
“Now these cars have ground effect, and have had for the last couple of years, which simply means that when the car does touch the ground, it [the downforce] all disappears.
“So you really have to be careful how aggressive that downforce is in those last couple of millimetres.
“It’s part of this genre of car, and it is something that is a trap that we've fallen into earlier in this season.”
Simulation problems
The issue with the cars operating in this narrow sweet spot between loads of downforce and it all being lost in an instant is compounded by the fact that teams cannot simulate this accurately in the wind tunnel.
F1’s current aerodynamic restrictions limit car models to be no greater than 60% scale, and there is a maximum wind speed of 50m/s – which is equal to 180 km/h or 111.85mph.
Considering that the critical speed where this peak downforce/bouncing dilemma hits is getting towards 200mph, it means there is no direct way to simulate it.
Teams are then having to utilise a bit of guesswork in terms of how things will cross over between the wind tunnel and the real world when they approach this critical point – but it is far from a perfect art.
Haas principal aerodynamicist Simone Benelli said that teams were trying their best to respond to warning signs – but they can never be totally sure.
“You come up with empirical metrics, which are based on physics at the end of the day, but it's all a simulation,” he said.
“You try to have some sort of experience base. But when you change floor concept completely, like we did in Silverstone, for example, you have to trust that the experience you build on a different concept is going to be still valid. It's not a simple one.”
The ability to predict things as accurately as required is made harder by the fact that wind tunnels cannot simulate perfectly how cars and aerodynamic parts interact with airflow as they transition through a turn.
Benelli added: “Low speed-behaviour is very difficult because you've got curvature.
“The wind tunnel model is in pure yaw, but the front wing is seeing wind from inside; the rear of the car is seeing much less, or even wind from outside.
“You generate a wake on the front with one yaw angle and that wake travels and hits the rear with a different [angle]. It’s not simply [a case of] saying, okay, the front is seeing minus something, plus something.”
Another factor, as Clear explains, is that wind tunnels are a clinically clean environment – unlike irregular track surfaces.
“The challenge is that what the wind tunnel sees is very pure,” he said. “You're not getting the bouncing that often gets initiated just by bumps, and the car bouncing off bumps, and which starts the aero bouncing initiative.
“But our models are getting better, and we are confident that we are now better able to get a little bit of that really, really aggressive downforce that you see in the bouncing, without initiating the bouncing.”
Another element too is that teams cannot find the actual physical limit of the track surface in the wind tunnel – because if the model floor touches the belt then there is the risk of a lot of damage being done.
As Benelli, whose squad uses Ferrari’s Maranello facility, said: “We don't want to smash Ferrari's wind tunnel. Obviously, in all the conditions where the car is touching the ground, it's not something you simulate in the wind tunnel, because you destroy both your model and the wind tunnel itself.
“So all of that is, what we say, operating outside the envelope. We try to maximise the [aero] map coverage – so that means a portion of the track that is actually covered by your wind tunnel map.
“But with this generation of cars it's super difficult. In the past, it [simulating the track] was almost complete, maybe end of straight, not – but in any case, we don't really care. This time, the high-speed corners in some cases are impossible to have [simulated] in the wind tunnel.”
An endless problem
This challenge of tricky cars and imperfect wind tunnel simulations means the problems that many teams have encountered with upgrades this year will not go away – and will likely hang around for as long as the current car formula exists.
And even for a team like McLaren, which appears to have been the least affected by developments going wrong this year, it’s not something it can ignore.
As chief designer Rob Marshall said: “The bouncing is kind of there on the edge the whole time. I think some people still experience it more than others.
“We do see it. We don't seem to have suffered particularly, but whether it limits us performance-wise, I think it's probably on the edge of limiting us.
“These regs have been with us for a while and they are much more limited in terms of what the aerodynamicists can play with.
“So I guess it's like scraping around the bottom of the jar for the last bit of lap time. You know, you've got a knife, now you're in all the corners. And not much comes out…”
