Rake- what does it achieve?

[SiLo]

Having seen Red Bull and Ferrari running quite a lot of rake last year, this year teams seem to be pushing it to the maximum, with cars almost looking bent in a bid to have the most rake but not upset the aerodynamics of the car on top.

What exactly does it achieve?

[scarbs]

It effectively makes the diffuser steeper, as they are so tightly rescricted on exit height.

[horse]

It's mostly to do with the down force generated by the floor and the diffuser I believe. By angling the floor up (while keeping the upper body level) you effectively make the underfloor more wing shaped which will improve the down force generated by the floor. It also increases diffuser angle relative to the ground.

This might also have an impact on the centre of pressure which (I'm really guessing) should move it forward. I'm surmising this as the region of greatest flow velocity will be at the leading edge of the floor as it will be the closest part to the ground.

[Belatti]

Last year I was at a team running two sport prototypes here in Argentina. I used to stablish the minimum height at the front and 5mm more at the back, give the kit car we were racing.

A suspension consultor told the team manager to increase 10mm the rear ride height for aerodynamic reasons. I told him not. He listened to the "expert" consultor = fail.

There were several things not taken into account, like the change of suspension geometry (more impact at the rear) and a thing one of the 2 drivers didnt like, plus driveshaft inclination beyond 10° (3 DNF´s cause of that, till they listened to me ).

Now I left the team, but still I wonder if that aero change would have worked given the time and resources to develop rear susp pick up points and engine/gearbox position to something more "logical".

[segedunum]

Now I left the team, but still I wonder if that aero change would have worked given the time and resources to develop rear susp pick up points and engine/gearbox position to something more "logical".

Possibly, but you have to live within what's possible with the mechanical side of things and you need solid mechanical wizardry if you're to make it work. Where they failed within your team was not speaking to you about the impact of increasing the rake and how you could make it work. They failed because they didn't see that there was a lot of development needed to go into that one, seemingly tiny, change.

That's why Adrian Newey has Rob Marshall.

[n_anirudh]

Usually rake is set up, so that the front wings are closer to the ground and can exploit the benefits of ground effect

[raymondu999]

At what point, though, does the lower ride height & CoG at the rear of the car outweigh the benefits of rake?

[marcush.]

static rake is one thing ,but really what you need to know is where your rake is in dynamic conditions and have an idea where your rake should be at certain points of the track.

Of course ..if your car is already borderline with mechanical setup and you try to play with rideheights to get the desired rake that can make it all tip over but 10mm static rideheight at the rear will not yield much in terms of downforce usually.So if something else is drifting away you got the mess of reality not matching expectations...and possible dnfs on top of it.

A sportscar with almost 10m²of bottom area has huge potential for producing ground effects downforce .But this will only work if you are producing something really precise and stiff facing the ground.To slam a piece of aluminiumsheet on the bottom and think it´s somewhat flat and hope for tons of downforce is not working.
As we have seen last year with F1 the hot exhausts baking/warping underfloors eroded all potential gains coming from the tricks that caused the overheating..

The smaller the throat of your flat bottom(small front ride height) the quicker your diffusser will be starved of airflow ,so small rideheights will not allow steep big diffusers and the transition between floor and diffusser is highly critical for angle and radius (precision as well).
F1 with their stepped nottom and sidepods starting only at half wheelbase will always have an entry height of 50mm to the stepped flat bottom ,starvation is not happening ,so you can exploit steeper difusser angles for the sides. To fill the centre section you may also need additional flow from the sides/stepplane.

[kilcoo316]

What exactly does it achieve?

Increases the area ratio between floor inlet (splitter/sidepod floor) and floor outlet (diffuser).

Thus more air for a given diffuser design.

[kilcoo316]

It effectively makes the diffuser steeper, as they are so tightly rescricted on exit height.

Being pedantic, they don't want to make the diffuser steeper*, but they do want to increase its exit height (well, area really). At the same time, they don't want to increase the splitter/sidepod floor height (cross-sectional-area).




*after all, a diffuser is a piss-poor substitute for real ground effect.

[scarbs]

Kilcoo, Fair point....