What is it about the current generation of F1 cars that has made them prone to porpoising?

Our readers’ questions vary from the highly technical to the ‘I always wondered why’ category. This one, from Stewart Moore, falls firmly into the former. He asks why the current cars are so prone to bouncing and porpoising, since even the 2021 cars relied on the throat effect of the flat bottom in front of the diffuser kick and therefore must have been prone to similar effects.

Looking at the 2021 machinery, these were effectively what were known as flat-bottomed cars. What this meant was that the floor could not have any real curvature in a fore/aft sense between the front of the floor and the start of the diffuser.

Rearward of this, which is essentially from the front face of the rear wheels, the floor was allowed to open up vertically in the area known as the diffuser. A limitation on the height of the trailing edge effectively limited the diffuser expansion, and hence the amount of load that could be generated by the floor.

More significantly in this context, the regulations dictated that two planes (horizontal surfaces) had to exist underneath the car. At the car centre line this plane, known as the reference plane, was the lowest part of the car and had to be at least 300mm wide and extend from 430mm behind the front wheel centre line all the way to the rear centre line.

This is the surface that the plank or skid block is attached to. Either side of this was what was called the step plane, which was 50mm higher and extended from the same forward position to the start of the diffuser.

The step plane, being relatively high, ensured that there was no chance of sealing the underbody to the ground. This severely limited the effectiveness of any ground-effect downforce generation and equally ensured that the underbody aerodynamics were very stable.

The way to generate downforce with these cars was to run very high rake; in other words a very low front ride height and very high rear ride height. This allowed expansion under the length of the car in the same way as a diffuser works, but left a large gap for the air to escape sideways.

This is why the so-called Y250 vortex was so important. This was a vortex generated by a discontinuity on the front wing, which twisted its way down the length of the car in an attempt to make an air seal at the edge of the floor and improve the underbody load.

Notable characteristic of the 2021 cars was very low ride height at the front and very high at the rear

Photo by: Mark Sutton / Motorsport Images

For the current cars, the design intent was all about producing a benign wake to mitigate the loss of downforce of following cars and bodywork that was also less affected by running in a leading car wake.

This was done to an extent by producing more underbody load by allowing more curvature in the floor and getting rid of the step plane in order to allow the throat, the lowest part of the floor, to be closer to the ground.

This greatly improved the amount of load that could be generated by the floor but, in order to generate that load, it now became imperative to run very close to the ground front and rear – very different to the previous generation of cars. 

The suspension was made very stiff to try to maintain low ride heights at both high and low speed – the natural tendency of course is that the car will be pulled down on its suspension as the speed and hence aerodynamic load increases.

Under the current regulations up to 60% of the downforce is generated by the floor and bodywork, the rest coming from the front and rear wings. With the previous generation of cars this figure was more like 50%

While the design intent of allowing cars to follow more closely was achieved, the combination of maintaining the throat of the floor very low and the very stiff suspension that this required resulted in an unstable aerodynamic condition.

This unstable condition arose from two areas. Firstly, if the throat got too close to the ground it could choke, limiting its flow and effectiveness, thereby reducing downforce. This in turn led to the ride height increasing and stability being restored.

Secondly, the vortices produced by the strakes at the entry to the floor underneath the radiator inlets could burst at low ride heights, which again reduced the effectiveness of the floor. This overstressed condition led to downforce being generated to a point where it forced the car too close to the ground whereupon the downforce diminished, and the car rose again such that downforce was regained. This of course is a thoroughly unstable condition.

To illustrate the importance of the floor, under the current regulations up to 60% of the downforce is generated by the floor and bodywork, the rest coming from the front and rear wings. With the previous generation of cars this figure was more like 50%.

The good news is that the 2026 regulations have found new ways of preserving good – in fact even better – wake characteristics while reducing the dependency of very low ride heights and unstable aerodynamic features, meaning that next year we can hope to see racing remain very close without the bouncing that the current cars exhibit.

Want to ask Pat a tech question for a future column? Let us know at autosport@autosport.com

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Next year’s regulations promise close racing without the low ride heights and aero instability that cause bouncing

Photo by: FIA