McLaren 650S Le Mans - question about louvres and downforce.

[acosmichippo]

Hello everyone,

I was just reading the press releases about McLaren's 650S LE Mans edition (BBC Article here), and this bit about the louvres over the front wheels sounded odd to me:

"Then there are the front wings with new louvres to reduce pressure over the front wheels and increase downforce."

Wouldn't reducing pressure above the wheels by definition also reduce downforce? Can someone explain how these things work?

Does it reduce pressure in the wheel well? That would make more sense.

Here's a pic for reference:

[Paul]

Exactly, they bleed the high pressure air, thus reducing lift/producing down-force.

[wesley123]

Yes, they reduce pressure build up in the wheel well and prevent air bleeding in the underbody by providing an alternate path. This reduces the lift.

[acosmichippo]

In that case, why don't more cars have them? Seems like a pretty simple way to increase downforce.

[Paul]

Probably balance. Road cars usually are designed with inherent under-steer, so more lift at the front is OK as long as there is similar lift being produced at the back.

[bdr529]

In that case, why don't more cars have them? Seems like a pretty simple way to increase downforce.

Sorry couldn't resist, it's the first thing that came to mind

[MadMatt]

As Paul said, you want under-steer on a road car, therefore, enhancing front downforce is not really wanted. What you want is to reduce rear axle lift. I have to add that a lot of the lift produced in the front wheel well is generated by the air pushing up under the tyre's front face (aka when you look at the car's left side from the side, the quarter at the bottom left).

[ylk1]

I believe TVR Sagaris had such vents in it's initial form. Then later, they removed them as dust and stones keep thrown onto the windshield. This was mentioned in the TopGear's episode too. May be McLaren 650S being a track car, they allowed them.

[No Lotus]

As Paul said, you want under-steer on a road car, therefore, enhancing front downforce is not really wanted. What you want is to reduce rear axle lift. I have to add that a lot of the lift produced in the front wheel well is generated by the air pushing up under the tyre's front face (aka when you look at the car's left side from the side, the quarter at the bottom left).

Yes. I have a patented retractable wheel fairing system and when deployed they defeat this lift, as confirmed by CFD. The same is true for the rears, but the lift back there is less marked.

[andylaurence]

I fitted louvres to my car and can confirm that rain/stones/grit/rubber come flying out of them. If it's wet, then the dirty water flows neatly over the bodywork making the car dirty in moments. On the flip side, the car's faster...

[acosmichippo]

seems like you could eliminate most debris by fitting a wire mesh in the louvres.

[MadMatt]

The positioning of the louvers is also very important. People tend to fit them as far up front as they can in a longitudinal plane, but I cannot really see any relevant research proving that concept. I believe it has to do with what I explained, the high pressure in front of the tyre, as there is indeed a low pressure area behind the wheel so why would you want to exhaust it on top of the car, hence the louvers located at the front of the wheel well.

[SectorOne]

In that case, why don't more cars have them? Seems like a pretty simple way to increase downforce.

Except that your "supercar" also needs to handle everyday life and having giant holes sending rocks straight up in the air is not so good for your car and others


If you´re talking about racing cars, they are there in all kinds of variations.

[J.A.W.]

Well now, y'all do realize that them good ol' NASCAR boys already done had them thangs.. `bout 1/2 a century back..

See here.. https://www.youtube.com/watch?v=N9ZSNM8MweA

[Cold Fussion]

In that case, why don't more cars have them? Seems like a pretty simple way to increase downforce.

Except that your "supercar" also needs to handle everyday life and having giant holes sending rocks straight up in the air is not so good for your car and others


If you´re talking about racing cars, they are there in all kinds of variations.

http://upload.wikimedia.org/wikipedia/c ... C_Fuji.jpg

That's purely by regulation. When rules for giant holes above the wheels weren't there, no LMP1 car run with such giant holes, they all featured louvers.