How to maximise downforce on flat floor+diffuser on race car?

[hsg]

If your main goal is to avoid front tyre wake entering under the floor, fences placed inside (inboard) of the floor edge are the better choice. Placing fences slightly inboard lets you catch and manage the dirty tyre wake before it spills into the low pressure floor area.

Main goal is to get maximum downforce with that floor, everything should be tailored to that goal.
One solution is use all floor area, second is use less floor area but with more quality airflow, which solution is better I dont know. If I have photos of of race cars floors I will come to conclusion which solution is better.

[Silent Storm]

If your main goal is to avoid front tyre wake entering under the floor, fences placed inside (inboard) of the floor edge are the better choice. Placing fences slightly inboard lets you catch and manage the dirty tyre wake before it spills into the low pressure floor area.

Main goal is to get maximum downforce with that floor, everything should be tailored to that goal.
One solution is use all floor area, second is use less floor area but with more quality airflow, which solution is better I dont know. If I have photos of of race cars floors I will come to conclusion which solution is better.

Right now you're trapped in a false binary...

It’s not “use all the floor and accept dirty flow” or “give up floor area to get clean flow.” Both solutions can work depending on execution...

The best solution is to use the maximum floor area available, while actively managing and cleaning the flow quality using fences, strakes, and tyre wake management.

Shrinking the floor area throws away huge potential downforce. The goal is to protect the floor, not delete it.

Every real aero car (LMP1, prototypes, even some touring cars) maximizes floor area and then uses intelligent flow control (deflectors, fences, slots) to maintain good pressure recovery.

Real world aero is always about finding ways to use what you have, not cutting parts away because flow isn’t perfect.

There’s no ready made answer or magic photo that tells you what to do. It’s always about applying principles to your specific situation and constraints.

[hsg]

If your main goal is to avoid front tyre wake entering under the floor, fences placed inside (inboard) of the floor edge are the better choice. Placing fences slightly inboard lets you catch and manage the dirty tyre wake before it spills into the low pressure floor area.

Main goal is to get maximum downforce with that floor, everything should be tailored to that goal.
One solution is use all floor area, second is use less floor area but with more quality airflow, which solution is better I dont know. If I have photos of of race cars floors I will come to conclusion which solution is better.

Right now you're trapped in a false binary...

It’s not “use all the floor and accept dirty flow” or “give up floor area to get clean flow.” Both solutions can work depending on execution...

The best solution is to use the maximum floor area available, while actively managing and cleaning the flow quality using fences, strakes, and tyre wake management.

Shrinking the floor area throws away huge potential downforce. The goal is to protect the floor, not delete it.

Every real aero car (LMP1, prototypes, even some touring cars) maximizes floor area and then uses intelligent flow control (deflectors, fences, slots) to maintain good pressure recovery.

Real world aero is always about finding ways to use what you have, not cutting parts away because flow isn’t perfect.

There’s no ready made answer or magic photo that tells you what to do. It’s always about applying principles to your specific situation and constraints.

Yes but my case 1. that you suggest me, is not that optimal solution. Case 1. is very dirty solution, inner front tire wake enter the floor 100%.
You can draw your solution

[Silent Storm]

Also, just to be clear, I’ve already given you a solution earlier...

Wheel arch vents or louvres can bleed off some high pressure pockets. Turning vanes at wheel trailing edge angled outwards rolls the wake away from your diffuser.

No solution fully stops tyre wake, even the cleanest race cars manage it, not eliminate it.

Case 1 is realistic, you use the fence to create longitudinal vortices that virtually seal the floor edge, improving the floor quality even if some tyre wake enters.

There’s no perfect isolation without enclosed tunnels, only smart flow management. That’s how real world ground effect works.

[hsg]

Also, just to be clear, I’ve already given you a solution earlier...

Wheel arch vents or louvres can bleed off some high pressure pockets. Turning vanes at wheel trailing edge angled outwards rolls the wake away from your diffuser.

No solution fully stops tyre wake, even the cleanest race cars manage it, not eliminate it.

Case 1 is realistic, you use the fence to create longitudinal vortices that virtually seal the floor edge, improving the floor quality even if some tyre wake enters.

There’s no perfect isolation without enclosed tunnels, only smart flow management. That’s how real world ground effect works.

Like this?
1. Isnt now enter X too small, how will this enter feed all floor?
2. that outwash fences will produce turbulence, isnt that bad for floor?

[The Rusted One]

The vortices from the fences can produce massive downforce if you manage it correctly like in the current ground effect F1 cars.

[Silent Storm]

Also, just to be clear, I’ve already given you a solution earlier...

Wheel arch vents or louvres can bleed off some high pressure pockets. Turning vanes at wheel trailing edge angled outwards rolls the wake away from your diffuser.

No solution fully stops tyre wake, even the cleanest race cars manage it, not eliminate it.

Case 1 is realistic, you use the fence to create longitudinal vortices that virtually seal the floor edge, improving the floor quality even if some tyre wake enters.

There’s no perfect isolation without enclosed tunnels, only smart flow management. That’s how real world ground effect works.

Like this?
1. Isnt now enter X too small, how will this enter feed all floor?
2. that outwash fences will produce turbulence, isnt that bad for floor?

https://i.ibb.co/mCKcTyg0/Untitled.png

You don’t need massive flow ingestion at the front... What matters is having clean, low energy air under the floor with stable pressure gradients. Modern underbodies control and condition the flow, not just dump huge amounts of air inside.

Also, regarding Case 2...
Case 2 sacrifices valuable floor area just to chase slightly cleaner entry flow, but it kills overall pressure recovery, ground effect strength, and diffuser feeding.

You win more downforce by using maximum effective floor area and managing the flow, not by shrinking the floor to avoid wake.

Fences absolutely generate vortices, but properly controlled vortices energize boundary layers, stabilize separation, and help maintain effective suction over the floor and diffuser.

“Turbulence” isn’t automatically bad... It’s about managing organized vortical structures versus chaotic separation. Current ground effect F1 floors, LMPs, and prototypes all use this principle.

[hsg]

The vortices from the fences can produce massive downforce if you manage it correctly like in the current ground effect F1 cars.

Current f1 cars will remove these fences if they are allowed to use side skirts?
F1 use fences because they must used them by rules or because they want to used them?

What is your solution for floor?

[The Rusted One]

The vortices from the fences can produce massive downforce if you manage it correctly like in the current ground effect F1 cars.

Current f1 cars will remove these fences if they are allowed to use side skirts?
F1 use fences because they must used them by rules or because they want to used them?

What is your solution for floor?

This isn't a F1 car 100% within the regs and I didn't make this car, but as you can see

The blue and green from the floor is where major downforce is generated from the vortices from the car. And as Slient Storm said

Fences absolutely generate vortices, but properly controlled vortices energize boundary layers, stabilize separation, and help maintain effective suction over the floor and diffuser.

Obviously in a unlimited rulebook, I don't know whether a side skirt will be better over a lot of variables (ride height, yaw, etc), but the floor fence solution seems to work for F1 teams in a limited rulebook. There's not a lot of examples with free reign over design, so there will never be a one size fits all solution.

In the case of a flat floor on a road car, the 992 GT3RS does have strakes next to the front wheels, so you can take inspiration from that. Along with the front diffuser and this really cool strake on the suspension arms. I think looking at stuff on production roadcars is more realistic than looking at prototypes (limited ruleset) or time attack cars (too extreme)

[hsg]

I think looking at stuff on production roadcars is more realistic than looking at prototypes (limited ruleset) or time attack cars (too extreme)

Do you think that production cars start use this outwash strakes from 2022, because they copy them from F1?
Are they here because they are cool or they are better then skirts?
I never see them before.

Why here write that diffuser can operate at 20° without flow separation? I think this is not possible, problem starts already above 8°

https://www.racetechmag.com/2017/08/wil ... diffusers/

[The Rusted One]

I think looking at stuff on production roadcars is more realistic than looking at prototypes (limited ruleset) or time attack cars (too extreme)

Do you think that production cars start use this outwash strakes from 2022, because they copy them from F1?
Are they here because they are cool or they are better then skirts?
I never see them before.

Why here write that diffuser can operate at 20° without flow separation? I think this is not possible, problem starts already above 8°

https://www.racetechmag.com/2017/08/wil ... diffusers/

Oh no, this isn't some new concept, Champcar/CART had these outwash strakes in the 90s. And the Porsche 992 GT3RS came out in 2022, which means development started years before the new F1 cars. And they are most likely not there to look cool. Why have stuff under the car that "looks cool" when you can have them in a visible place......

As for the diffuser angle, I think you have too much of a binary view of aerodynamics, as others have said. It depends on a lot of variables that without CFD, is really hard to make sure. If the diffuser is made poorly, it could separate at super low angles and vice versa, if made well can get to very high angles...