Front Wheel Air Deflectors

[Redd]

I'm thinking of getting an Mporium alu skid pan. This is an all flat piece which means that the front wheel air deflectors (the stock triangle felt pieces) will be removed. I can easily replace air deflectors using E9x non-M parts, but wondering if it's actually worthwhile purely from a performance/handling standpoint (I don't care about fuel economy).

Been doing research on this and have mixed views:

1. GT86/FRS and S2000 owners add them and it supposedly improves front end handling.

2. One Prius owner built his own alu undertray and then added air deflectors and he found that it improved fuel economy but made front end handling worse.

3. Porsche 718 GT4 has them, but the manual recommends owners remove the front wheel air deflectors for trackdays or when the rear wing is set at a high AOA.

4. Porsche 991 GT2 RS Clubsport doesn't have the front air deflector, but the 992 Turbo S does.

I'm so confused! Any input is appreciated.

[roastbeef]

it is highly dependent on the car, that is why you're reading conflicting instructions on when to run them.
aero like this is tricky, and its hit and miss without wind tunnel testing. it isn't as easy as a splitter or a wing. if the car has them, run them.

[omgzirra_exe]

1. GT86/FRS and S2000 owners add them and it supposedly improves front end handling. ;- if they have a front splitter it helps.

2. One Prius owner built his own alu undertray and then added air deflectors and he found that it improved fuel economy but made front end handling worse. - hybrid owners are weird they will do anything for extended miles, a flat undertray would work better with fins to reduce air tumbling in the rear.

3. Porsche 718 GT4 has them, but the manual recommends owners remove the front wheel air deflectors for trackdays or when the rear wing is set at a high AOA. - this is correct, the front splitter on the GT4RS doesn't produce enough downforce with a high rear AOA.

4. Porsche 991 GT2 RS Clubsport doesn't have the front air deflector, but the 992 Turbo S does. - the GT2RS fenders already reduce air pressure under the wheelwell already so it does not need front deflectors to redirect air around the wheel/tire

[Redd]

Originally Posted by omgzirra_exe

3. Porsche 718 GT4 has them, but the manual recommends owners remove the front wheel air deflectors for trackdays or when the rear wing is set at a high AOA. - this is correct, the front splitter on the GT4RS doesn't produce enough downforce with a high rear AOA.

So based on this, removing the front air deflectors theoretically should produce more downforce/grip over the front axel?

[LakeSurfer]

My aerodynamics knowledge is limited and only based on what I learned from my aviation degree.

To create down force (from a wing standpoint) you would need a curved surface paired with a rounded surface to create lift. Up force requires a curve on the top and flat on the bottom and down force would be the opposite. This is very general though.

So in regards to any under tray creating any type of force it would depend on the upper surface. In this case the hood and the rest of the upper surface of the car and the rest of the undercarriage for that matter.

The car has a more round upper surface and adding more flat to the bottom seems like you would be creating more lift and therefore reduce downforce and that would or could make steering at speeds worse?

The car would be more aerodynamic and produce cleaner air off the rear but at a cost of grip. So I would think you would need to counter act all those new forces and add, I don't know, splitters and a wing or something?

I also don't like those flat trays because they attach to the bumper cover which is flat and needs to be straightened to get them to fit. The install puts tension and stress on parts of the bumper that is currently installed in a relaxed stress free way.

All of this is probably why they work well on some cars and not so well on others. It all depends on the upper surfaces.

But at the end of the day I have no idea what I'm talking about.

I'm sure BMW didn't get everything right on this car but flat under carriages have been a thing long before our M3's so why didn't they make them flat from the factory? They tested the car in wind tunnels and computer simulation. Plus it was probably way more expensive to build the OEM set up then it would ha e been to build a flat 1 piece part.

Just my thoughts

-Mark

[Bimmer Barney]

My 335i oem undertray was flat. The M3 is not. To me, seems very intentional and agree it appears to be higher cost to build the M3 pieces.

[Redd]

Originally Posted by Bimmer Barney

My 335i oem undertray was flat. The M3 is not. To me, seems very intentional and agree it appears to be higher cost to build the M3 pieces.

The E9x non-M have these pieces that attach to the flat undertray.

https://www.fcpeuro.com/products/bmw...136525#fitment

Not sure why they didn't use it for the E9x M3. It looks a lot tougher than the stupid triangle felt pieces.

[Bimmer Barney]

Originally Posted by Redd

The E9x non-M have these pieces that attach to the flat undertray.

https://www.fcpeuro.com/products/bmw-pressure-lip-seal-front-left-51627136525#fitment

Not sure why they didn't use it for the E9x M3. It looks a lot tougher than the stupid triangle felt pieces.

I don't remember those on the front tray but maybe I'm just forgetting.

[Redd]

Originally Posted by LakeSurfer

I'm sure BMW didn't get everything right on this car but flat under carriages have been a thing long before our M3's so why didn't they make them flat from the factory? They tested the car in wind tunnels and computer simulation. Plus it was probably way more expensive to build the OEM set up then it would ha e been to build a flat 1 piece part.

I'm not convinced that every decision made around the M3 is a performance decision. Perhaps those deflectors are there for fuel economy, I don't know. If deflectors have such aero benefits, all performance models would have it. But we see it also on normal Fords, Prius, etc, and some extreme performance models like C7 ZR1 ZTK removes them (but ZR1 has them). Hence my confusion.

[LakeSurfer]

Originally Posted by Redd

I'm not convinced that every decision made around the M3 is a performance decision. Perhaps those deflectors are there for fuel economy, I don't know. If deflectors have such aero benefits, all performance models would have it. But we see it also on normal Fords, Prius, etc, and some extreme performance models like C7 ZR1 ZTK removes them (but ZR1 has them). Hence my confusion.

I agree. I would be surprised if they helped fuel economy. A flat surface at the leading edge of the car, seems like they would hurt it.

I was thinking that they're sort of an afterthought and maybe help out with cooling the engine, oil or radiator? Perhaps they designed the front and were already committed to it and found that the air in the engine bay wasn't flowing properly so they came up with these things to help.

[Redd]

Been doing a bit more research on this topic. Julian Edgar, published aerodynamicist, has a lot of info on the subject of front wheel deflectors.

This video talks about how front wheel deflectors reduce drag which has a direct improvement on fuel economy.

http://origin.autospeed.com/cms/titl...2/article.html

In his article above, he references a Volvo study on front wheel deflectors of various sizes. In almost all cases, front wheel deflectors decreased drag but increased front end lift. He then goes on to test it on his own Prius with similar results.

The article is an interesting read. Sounds to me like the deflectors are there for drag/fuel economy, which also explains why high performance vehicles remove them.

[LakeSurfer]

Originally Posted by Redd

Been doing a bit more research on this topic. Julian Edgar, published aerodynamicist, has a lot of info on the subject of front wheel deflectors.

This video talks about how front wheel deflectors reduce drag which has a direct improvement on fuel economy.

http://origin.autospeed.com/cms/title_Modifying-UnderCar-Airflow-Part-2/A_113182/article.html

In his article above, he references a Volvo study on front wheel deflectors of various sizes. In almost all cases, front wheel deflectors decreased drag but increased front end lift. He then goes on to test it on his own Prius with similar results.

The article is an interesting read. Sounds to me like the deflectors are there for drag/fuel economy, which also explains why high performance vehicles remove them.

So I wonder if you directed the cooling air up and out of the wheel fenders you would increase downforce and have better handling?