Presented by Nine Lives Racing
Ed Higginbotham
Ed Higginbotham UberDork
9/28/21 9:22 a.m.

So I was sitting around staring at my empty shell of a race car ('95 BMW 325i), thinking of things to remove for weight savings. I still have the front fender liners in there. It's just a couple pounds but it got me thinking. Is it possible that they serve any kind of aero purpose? There's a nice big parachute shaped hole inside the rear of the fender that is covered by the fender liner. Even if it's just the slightest advantage one way or another, does anyone have an opinion on this? Will an E36 even be going fast enough for it to matter?

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
9/28/21 9:31 a.m.

Probably the largest possible effect is brake cooling. 

Iirc, the E36 has cutouts in the front of the front fender liners with a little deflector to push air to the rotor.

If you've got different brake cooling in place, then maybe not so useful anymore.

But also, the wheels are awful aerodynamically. You do ideally want them sealed off from the underbody flow. Vents above the wheels work to relieve high pressure air from the wheel wells (because otherwise it would invariably bleed under the car where it isn't ideal).

Ed Higginbotham
Ed Higginbotham UberDork
9/28/21 9:48 a.m.

Hm okay that's good info. There will be dedicated brake ducting so I'm not super worried about that. 

I can't run any kind of vents since this is a spec series, but is it possible the cavity behind the front wheels would help expel the that high pressure from the wheels?

Again this is all probably just academic in my application but any little bit helps. 

I wonder what people do on cars where it actually does matter. Like does a land speed car have smooth, tight wheel wells?

dr_strangeland Reader
10/16/21 3:40 p.m.

LSR cars are a bit weird, at least if you're going supersonic. I couldn't find good details on, say, Bloodhound. Those wheels are extremely narrow and might not be a useful comparison.

I'm just going to go out on a limb and say if you could reduce air pressure in the wheel well you would reduce drag. Like, if there was no air pressure in there, there would be no drag. If BMW is trying to create negative pressure in there, that would make a lot of sense to me. 

I think the liners are mostly practical on a street car. The less clearance there is over a wheel, the more drag you'd expect due to surface effects. 

The practical effect on a street car is likely to be minimal.

pushrod36 Reader
10/22/21 7:32 a.m.

If you don't have a hood vent opening the fender liner can be a good way to extract high pressure from under the hood.  Multimatic did this on the GT350R-C.

jh36 HalfDork
10/23/21 9:59 a.m.

Does spec3 allow hood or fender venting?  Doubtful, but if they do, I would fold that into this equation. 

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