E30 Aerodynamics request

[EtaSax]

When BMW tested the iS spoiler, they found a 2% reduction in turbulence at the rear. I cannot source that, as I merely read it somewhere and it may be completely made up.

I just wonder what kind of effect that actually has on performance and if it affects downforce. I'd imagine that the iS spoiler does indeed reduce drag by lessening the effects of the low pressure pocket at the rear of the car, but does it affect downforce as well? Shouldn't downforce be clearly visible in these proposed pictures as flow of air in an upward path extending from the top of the bootlid or would it be very subtle? That is, of course, if the differences between spoilers are indeed visible at all.

[2mAn]

makes me want an mtech1 spoiler

[Gleb]

.

[ELVA164]

I just wonder what kind of effect that actually has on performance and if it affects downforce. I'd imagine that the iS spoiler does indeed reduce drag by lessening the effects of the low pressure pocket at the rear of the car, but does it affect downforce as well? Shouldn't downforce be clearly visible in these proposed pictures as flow of air in an upward path extending from the top of the bootlid or would it be very subtle? That is, of course, if the differences between spoilers are indeed visible at all.

I would expect that the effect on downforce would be extremely negligible if existent at all. The flow of the air over the spoiler would not directly correlate to a downforce measurement; there are too many other factors to consider. For example, a large amount of downforce on a wing may result in a large deflection of the airstream, but something like a twin-plane wing could produce a similar number with less deflection at each surface. Or if there were something like a gurney flap on a flatter plane as opposed to a larger plane with a less aggressive lip, they could provide similar amounts of downforce with different effects on the airstream as seen in your situation.

[bastianshaw]

I think the IS spoiler adds like 100lbs of downforce at 60mph. But you have so much drag that you can't accelerate much faster than a Prius.




Totally serious. ;-)

source?

[bastianshaw]

simple thought would be have a car with and a car without spoiler follow each other a few hundred yards apart and take pics/video. rules out variables on temp/wind/water.

i doubt it is that much of a difference. likely to have more spray difference due to tire tread/size, ride height, mudflaps, bumper design, etc than spoiler/no spoiler.

that rules out variables?

[bastianshaw]

.

nice

[downforce22]

spoiler > no spoiler

Trust me, i know downforce.

[EtaSax]

simple thought would be have a car with and a car without spoiler follow each other a few hundred yards apart and take pics/video. rules out variables on temp/wind/water.

i doubt it is that much of a difference. likely to have more spray difference due to tire tread/size, ride height, mudflaps, bumper design, etc than spoiler/no spoiler.

that rules out variables?

I don't think those variable would even matter. It is the shape of the spray we are looking at, not the amount. The shape would tell us about the actual aerodynamic effects. Amount of spray would tell us everything that we aren't looking for.

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