DTM cars: fins behind the rear wheels

[PNSD]

Anyone want to explain what all the fins do at the back behind the rear wheel? Ive never understood the design philosophy of DTM cars and looking at this years Audi A4 it looks very messy at the back. If anyone could shed any light that would be nice.

[vyselegend]

I've always thought they were producing downforce, but now you question it, I have doubts, especially looking at it on the mentionned car, that part has become so hollow! I think the main consequence of this design (by opposition to a "filled" rear soulder), is about weight reduction. Then, looking at the pic, it obviously has something to do with rear wheels turbulences management, maybe the upwash produced by the rotating rear tyres can be smoothed out that way, reducing overall drag...

Just a wild guess. Waiting for the aero guys to explain it fully.



Although this is probably unrelated, note that the front flip-ups (those looking like sportcar's ones) are very similar in shape and angle.

[zac510]

I'm sure the original placement of them had merit but a few years on the cynic in me tells me that they're mainly there to reinforce the look, style and 'image' of the DTM series.

[PNSD]

About the front ones, they're called dive planes... apparently very efficient, low drag high downforce devices depending on the posistion.

I hope it is much more than just being their for looks really !
Ive always thought it must be something to do with the wheel rotation but what I dont know!

This years Audi A4 has 6 of these flipup style things!!

All looks very messy.

[vyselegend]

I'm sure the original placement of them had merit but a few years on the cynic in me tells me that they're mainly there to reinforce the look, style and 'image' of the DTM series.

Yes I see your point. The overall look is quite extreme, the tunning ricers would typically love that sort of design on their car. I doubts car spending most of their time between 100 and 200 km/h would rely so much on aero anyway...

Still, both Audi and Mercedes are extremely serious about the DTM, I don't see them jerking around with ridiculously sized aero bits just for the fun of it. Having just watched the opening round at Hockenheim (men, that was the most borrying DTM race I've ever seen ), I'm impressed by the pace of the 2008 spec A4. For sure this "messy" arrangement didn't slow it!

Double-thinking about it, it probably also helps extracting hot air from the brakes...

Speaking of the brakes, the speaker on Motors TV mentionned two paddles were fitted behind the steering wheel, one acting like a handbrake, and the other is told to command a cooling device for the brakes! Anybody knows how it works exactly?

[mx_tifoso]

I don't believe that the rear end 'flipups' are for reducing weight, since if they were to be pressed down they would fill in the gaps made by their current position. And it would appear to me, at least, that only the top 'flipup' serves an [incoming] aero purpose, to produce downforce that is. Since the rest underneath are highly affected by the rotating tire, so as other people have mentioned, are probably meant to clean up the disturbed airflow and reduce rear end drag. Or maybe the ones underneath do produce downforce, in conditions where the car is not running perfectly straight, such as when turning, the only conditions where the 'flipups' under the very top one face "forwards" (so to speak) (?).

And I agree with the notion that DTM cars have a very 'messy' look to them.


PS. The subjective comments above are from a business student, so as you can tell I don't know [much] about aerodynamics.

[Scruffy]

The turbulence created by the wheel and tyre, the air flow from the brake cooling through the wheel and the air flow along the side of the car.

To gain some control over the air movement the aerofoils are reliant on the overall speed of the car to direct the flow into the vanes and increase the down force on the rear.

Quite simple really. Three different flows, redirected to add to the overall efficiency of the rear end.

DTM don't do decoration on cars, very utilitarian and efficient

[vyselegend]

Hi Scruffy, welcome to the forum.

Still had no infos about that, so I give it a little "up":

the speaker on Motors TV mentionned two paddles were fitted behind the steering wheel, one acting like a handbrake, and the other is told to command a cooling device for the brakes! Anybody knows how it works exactly?

Anyone heard about it as well? What sort of additional cooling could you bring to the brakes? Variable brake duct's intake maybe?... I'm puzzled by this.

[roost89]

Hi Scruffy, welcome to the forum.

Still had no infos about that, so I give it a little "up":

the speaker on Motors TV mentionned two paddles were fitted behind the steering wheel, one acting like a handbrake, and the other is told to command a cooling device for the brakes! Anybody knows how it works exactly?

Anyone heard about it as well? What sort of additional cooling could you bring to the brakes? Variable brake duct's intake maybe?... I'm puzzled by this.

I've done some googling and I came across this: http://www.gmeurope.info/social_media_n ... 20626.html it has a wee section on brake cooling. It basically says that DTM have allowed upto a 5 litre tank of water for cooling the brakes. They get sprayed with water via a button on the steering wheel when coming into the pits.
I can imagine they'd be used to cool the brakes at other points aswell. The article is from 2002, so it will be a bit dated. I'll have a look for a newer one.


I can't imagine what the hand-brake would be used for on a track-car. Rally yes, track no. Anyone shed some light on this?

[vyselegend]

Thank you for the information! From what you say it's not a very recent system! Yet I wasn't aware of it at all. Sound so simple, water on the discs...

Maybe the handbrake's purpose is just to lock the car while on the grid or in the stand (and the driver is not in it). Like handbrake's purpose in any car. Come to think of it, the only reason F1 doesn't need handbrake is because it is dismounted before travelling, it never needs to stand still with the tyres mounted and no driver inside.

[zac510]

DTM don't do decoration on cars, very utilitarian and efficient

How do you know this, do you work in DTM or just believe the hype?