Functional rear spoilers?

[2mAn]

I take laxatives before I race, every pound counts.

Im going to sand my car down to bare metal eventually, but first I must take care of aerodynamics :hitler:

[blue plates]

Hahah

[TheTacoMan]

M3 style or this is what I would consider if you want the look.

[2mAn]

function, not for looks. that looks like it would cause a lot of drag...

which brings me to a semi functioning brain. I dont really know what the goal here is, downforce perhaps

[Liquidity]

Maybe it would cause a lot of drag if the air flow behind that nearly vertical rear window wasn't almost stagnant. The spoiler is barely in the flow of air, it needs to be aggressive like that if it's to do anything.

[MPLFoster]

M3 style or this is what I would consider if you want the look.

What spoiler is this? looks like the Rocket Bunny S13 wing...

[Bearmw]

My car is hardly slippery but I run a plain later eta front lower lip on my vert (I don't run an oil cooler on my m30). I like to imagine it makes some sort of difference plus I like the plain look without the oil cooler opening.

They say the factory plastic engine undertray makes a difference as well. Also I notice that some later cars have the small aluminum tray that covers most of the trans. It has to make some kind of difference or BMW wouldn't have added it.

[Liquidity]

What spoiler is this? looks like the Rocket Bunny S13 wing...

RPerformance is the brand.

http://rperformance.blogspot.com/p/product.html

[Sykohtic]

My car is hardly slippery but I run a plain later eta front lower lip on my vert (I don't run an oil cooler on my m30). I like to imagine it makes some sort of difference plus I like the plain look without the oil cooler opening.

They say the factory plastic engine undertray makes a difference as well. Also I notice that some later cars have the small aluminum tray that covers most of the trans. It has to make some kind of difference or BMW wouldn't have added it.

Totally agree. BMW wouldn't have put it there if it didn't have a purpose. The only reason I keep running my car without an undertray is pretty much because I keep breaking them through extenuating circumstances, and probably also because I'm too cheap to buy a repop and just keep using ones I find laying around that are as brittle as a gingerbread wafer...

Really, if you wanted a cool project you could go through a figure out how to mount covers all the way back for the engine, trans, drive-shaft, diff and half-shafts and then build a mild rear diffuser. As long as you vented it properly so as not to cause too much heat build up anywhere, doing that would really lover some drag with a properly matched valence. Add in some good ducting to feed the brakes front and rear and you'd be set with something better than factory, assuming you kept the weight down.

Interesting...i'd like to know as much info about my Hartge spoiler as possible. Was wondering if there is any benefit to either drag coefficient or down-force.

I think the Hartage Spoiler is a lot like the Pfeba Heckspoiler that's going on my car, if the spoiler you're talking about is on the car in your sig. I know that my Heckspoiler is considerably bigger than my IS spoiler, and definitely stretches back off the deck-lip farther. I haven't been in any sort of wind tunnel, but from my dose of knowledge in aerodynamics, I'd say it definitely is gonna add some downforce over the IS spoiler. A marginal amount of downforce, but downforce all the same. As far as drag goes, I don't really see how it can add all that much drag considering there's not much direct airflow at the forward edge of the spoiler.

As dumb as it sounds, I'd honestly be even interested to know what the effect of even raising the sunroof up does to the aerodynamics of an E30.

I've always understood that downforce is negligible at speeds under 100 mph with just about any wing on any car.

I'm not sure about that... I'd say downforce starts becoming a thing around 65-70 no?


--Mike

Actually, you're both a little high. The effects of downforce, drag and airflow are a thing even down to like 45 miles and hour. Downforce itself really becomes a thing around 45, 50, 55-ish, though if can be seen having a sort of effect even before that. Reason I know is because for a project I was part of an experiment with using the rear hatch of a Honda Insight as an airbrake for a Bonneville prepped Honda Insight lol Never got to run the car or test it in the wind tunnel, but the testing was done on the open road in the back of a modern Insight with a simple scale rig set up attached to the rear hatch and setting the cruise control to 55; you cant get much more real world than that. I wish I still had my sheets and math to show you all, but you'd be surprised how much downforce (and drag too in some cases) was generated at only 55 mph, given we are talking about a trunk hatch with quite a lot of surface area versus a wing off the deck lid behind a pretty boxed off roofline.

[roznic]

I am interested to know the stats on Mtech 2 spoiler or kit in general if any?!

[2mAn]

found this pic and it really makes me wonder

[Sykohtic]

found this pic and it really makes me wonder

This is one of the biggest mistakes most people make whenever they look at aerodynamics visually. Smoke is NOT a very good indicator of airflow, and it's only because of commercials and tv that people think it is. Smoke is not as fluid as air, doesn't flow and move as freely, and also disperses fairly quickly off the roofline of cars like ours. I assure you the spoiler of the car i the image is working, else that was an extra few pounds BMW could have saved from the trunk, rear sail, and wing to put or use somewhere else. Also food for thought... not all spoilers are for downforce alone. Many actually direct airflow in such a way as to improve the airflow off the back of the car and reduce aerodynamic drag, with downforce being actually a secondary byproduct. Examples of this are the active aerodynamics on a 1991-95/6 Mitsubishi 3000GT VR4. The active-aero serves more to make the air flow over/under/around the car more smooth, and improve airflow off the tail. Downforce is a byproduct and happens naturally as the redirected airflow does more to reduce lift than actual air pressure on the wing, which also translates to higher stability at high speeds.

There's a reason that M3's have a rear sail, raised trunk lid, and all those extra body bits. The E30 M3 was a racecar, and functionality was quite a bit more important than form. If it didn't need to be there, it wouldn't have been. It is also possible the aerokit served more to optimize airflow as I stated before instead of actually directly targeting downforce itself. This would explain gurney flaps, as it would detail people wanting to increase the amount of actual "dowforce focusedness" the rear of the car had.

Long story made short, actually putting your car in a real windtunnel on the scales is the only method by which you can tell what difference each wing is actually making. Smoke wont tell you very much, and (no offense intended) is usually a device used to show off to people who don't know what their looking at or to make aerodynamics visual for a photo-shoot or a commercial where the viewer otherwise couldn't actually see what was going on in the windtunnel.

[nando]

people don't even have the basics right.

a spoiler disrupts the turbulent air at the rear of the car, making it more aerodynamic by reducing drag.

a wing provides downforce. it increases drag.

E30 M3s have wings. regular E30s have spoilers.

also, the stock is spoiler actually is effective at what it's meant to do - reduce drag.

Seeing how the M3 was built for racing, I'm going to hazard a guess that BMW put a wing on it that does what it's supposed to do. In fact most of the race cars used the same basic wing, but made it more effective with the big DTM flap.

also, the entire point of redesigning the rear window and trunk on the M3 was to make the wing more effective by raising it up and making the transition less steep.

[Sykohtic]

people don't even have the basics right.

a spoiler disrupts the turbulent air at the rear of the car, making it more aerodynamic by reducing drag.

a wing provides downforce. it increases drag.

E30 M3s have wings. regular E30s have spoilers.

also, the stock is spoiler actually is effective at what it's meant to do - reduce drag.

Seeing how the M3 was built for racing, I'm going to hazard a guess that BMW put a wing on it that does what it's supposed to do. In fact most of the race cars used the same basic wing, but made it more effective with the big DTM flap.

also, the entire point of redesigning the rear window and trunk on the M3 was to make the wing more effective by raising it up and making the transition less steep.

I mostly agree, and the last three parts of your post are essentially what I was saying, you're just being more specific and condensing my expanded statements, which is a good thing, so thank you. I will note additionally, however, that the OP was more interested in knowing more about the most effective spoiler for the back of his car from an overall standpoint (general balance between low drag, dowforce, etc.) than actually debunking the effectiveness of the non-M3 stock IS spoiler (at least he wasnt originally).

I will say, while you detailed wings and spoilers as white and black, they're more incremental and mixed than that. Im sure you were being intentionally basic and specific, but there are spoilers that serve a high dowforce focus. Examples would be NASCAR. Those are spoilers, but they definitely have a very strong focus on downforce as opposed to optimizing airflow (not that they don't also work to that purpose as well). The 3000GT VR4 I mentioned oppositely uses a wing. It is detailed as a wing by Mitsubishi who built the car. This wing's purpose with the VR4 active-aero feature is to optimize airflow along/over/off/under the car. It DOES produce downforce as well, make no mistake, but dowforce is NOT its full focus. Also, by white and black definition, how do you define the setup on, say, the McLaren P1 which has an active-aero system to use as airbrakes, dowforce, stability, AND drag reduction at high speed? However, that is NOT to say you are at all wrong about the setup on the E30 M3, as your description is synchronous with mine.

[nando]

yeah I agree with you. I think you posted yours while I was still typing mine.

still, I think the distinction is important. shopping cart wings from the F&F days are definitely not for the same purpose as an is trunk spoiler. :p