Aerodiscs at the track?

[bronco100]

Supposedly they create extra downforce and improve brake cooling. Does anyone know if that's actually the case? Particularly for the Rotiform aerodiscs as they are probably the most popular. If it's true then surely I'd see these more often at the track?

 

[Mad Hatter]

I guess the direction of flow would be important, so the don't clash with any brake ducts etc. Wasn''t this quite the in thing in the 80's?

 

[mavisky]

They're as much of a style statement now as an effect. If there was a strong benefit to running them we'd see them being used at World Time Attack I feel and I can't recall seeing a single set.

 

[Bill Pemberton]

But after the event you can use them at the local Frisbee Disc Golf Course!

 

[Vettel-ish]

Porsche does on the MR kits they have for the gt3rs. That car is a nurburgring weapon.

 

[mavisky]

Porsche does on the MR kits they have for the gt3rs. That car is a nurburgring weapon.

True, but those are more flat disc's to smooth the air going around the rear of the car vs these which are vented, finned, and attempting to serve as an active part of a cooling solution and actually protrude out into the airflow

 

[JDee]

View attachment 88343

Supposedly they create extra downforce and improve brake cooling. Does anyone know if that's actually the case? Particularly for the Rotiform aerodiscs as they are probably the most popular. If it's true then surely I'd see these more often at the track?

I thought those were only to cool brakes? Going way back in the day to when Audi ran a couple of 4wd weapons in TransAm, they had those disc's on the wheels. I spoke to Walter Rorhl (think that was his name) who drove one and he said brake cooling was their use. Those cars were 4wd turbo 5 cyl if I recall correctly and they were supposed to be making around 1000 hp and they needed all the brake help they could get, tires being what they were back then.

 

[bronco100]

It's very interesting for sure. I think it's got to be more for looks than anything, but I'm sure there's some aerodynamic and/or thermal effects, whether positive or negative, so I'm surprised it hasn't been studied more. I happen to think it looks really neat, particularly in the SEMA build Mustang pictured in my original post. I think it may be a bit of a trend as well, as seen on all of the new RTR FD Mustangs.

 

[bronco100]

They're as much of a style statement now as an effect. If there was a strong benefit to running them we'd see them being used at World Time Attack I feel and I can't recall seeing a single set.

I agree! But also, they can be found on some time attack cars!

For example, the Industry Garage 240z.


And the Evasive Motorsports S2000.



Perhaps @AJ Hartman could comment?

 

[mavisky]

Of your two examples, the S2000 one is like the Manthey Racing aerodiscs that are flush with the outer edge of the wheel. I fully believe that this would work to smooth airflow down the sides of the car.

In regards to the Industry Garage 240z, I don't know how much trust I'd put into any of that car being "aero tested" as the pictures I find online seem to show about 8 different configurations and none of them seem to show it with a rear window at all which we can all agree would terribly disrupt airflow to any rear spoiler or wing they have back there.




Based on your multiple posts abour aerodisc wheels and vented fenders it seems very obvious that you want to build a time attacked themed time attack car, and I don't want to seem like I'm trying to stop you. Just understand that sometimes it's more about style than performance.

In watching some videos towards the buildup of the new RTR cars for this season I think they were mentioning running them in an attempt to suck smoke out from under the fenders to make their smoke trail wider as that would make it more difficult for their competitors to chase them while drifting. They certainly don't need more brake cooling on the rear axle of their drift cars. James Deane runs some on the front of his new FD RX7 drift car and it's 100% for style on his build

 

[Dave_W]

Just understand that sometimes it's more about style than performance.

Or to have more parts you can sell to people who think they're cool.

attempt to suck smoke out from under the fenders

Ha! That's exactly what I was thinking.

To get a real brake cooling effect, it's not just the disc or even mostly the disc - the wheel spokes and/or disc mounting tabs (and you need a lot of them) have to act as radial fan blades like in a turbo compressor wheel. Imagine if you only had the outer 10-20% of each blade on the compressor wheel - that's what that wheel design is trying to do if it's done right. It's the same thing as the vanes in a vented brake rotor are doing.

 

[JAJ]

The first time I remember seeing these things was in pictures of the Porsche 935 race car in the 1970's. No! Wait! I actually saw them in person! I took this photo of Peter Gregg in the Brumos Porsche at my local (Westwood) track in Vancouver in 1977:



I've wondered about using them occasionally over the years, but the challenges always seemed to outweigh the benefits. First, which way does the air go? If it's pulled in, then it messes with all the aero that's trying to create low pressure under the car. If it flows out, it disturbs the airflow around the car. Either way, it could create unbalanced brake cooling - making the outer face of the disk cooler than the inner face. Now, if you've got 850 turbocharged HP and an endless supply of new brake rotors, you can overcome the problems regardless, but that's not most of us.

As an aside, I never saw the 935 close up, but I did get a guided tour of a "disassembled" 934. It was a "mid-engined" Porsche. For these cars, you could get reverse-pitch final drive gears. With the special gears you could remove the engine and gearbox, turn it 180 degrees and reinstall it so the engine was in front of the rear wheels with the gearbox in the space at the back where the engine used to be. It sounds unbelievable, but that's how the 934 was set up. Must have made for a very warm drive... Thing was, set up that way there was plenty of room back there for big cooling ducts and big turbos, along with improved weight and balance and lower rotational inertia. Stunning.

 

[bronco100]

First, which way does the air go?

Surely someone in here is a CFD expert, get on it!

 

[Mistaricky]

I'm no aero/ cfd expert. But I personally loves these and want to put some on my build as well. From what I've read online the smooth ones, that do not have fines like on the GT3RS MR are done in an effort to reduce drag, which, will give smoother cleaner air to the wing or potentially diffuser. You can find smooth style wheel covers on a lot of economy cars and many economy cars have minimal holes. Think how the base model 3 wheel covers reduce drag to gain range and they have very little openings.
I haven't read anything online from porsche or others stating this would help rear brake cooling. If anything I would think it hurts brake cooling in the rear because there is less open area for the heat to extract from.
Don't quote me on this, but I'm pretty sure we don't see turbo fans or fin aero discs on front anymore is for
1- in wheel to wheel, it would likely make debris really easy in case of contact. So that is likely outlawed
2 - you're adding drag to cool, front brake ducts will likely be a better drag to cooling ratio. I'm sure they do help cool the brakes if well designed with fins, but in my opinion you are likely making too much drag. We all know your tires are bad for aero because they're rolling which is why we need to vent the top and rear of our fenders or even guide the air away from the wheels like with spats or canards. adding these also effectively makes your car wider so you inevitably add more drag with more frontal area.
I imagine the flat/ smooth discs up front would help to also reduce drag. But the front brakes get significantly hotter than the rears and I'm sure the higher end builds only put the smooth discs in the rear because the rear brakes don't get as hot.
I personally would run a smooth rear disc to reduce drag just like the GT3RS MR. I probably wouldn't put anything in the front. I personally also wouldn't add any turbo fans or fin discs from a performance aspect.
I'm no expert, just another track rat thinking out loud. I'm sure AJ could give way more valuable opinions. Hopefully this helps someone. In the end of the day, do what you want to your car to make you happier whether that's with cosmetic or competitive intentions.

 

[Mistaricky]

Also, F1 has a long history of wheel covers. the current designs are really flat and I believe that was done in an effort to make drafting or chasing down another car easier.
If you go back about 10 years or more, teams were trying a large range of wheel covers. Some stationary, some attached to the wheel, some with intakes, some without. I'm sure some of those designs could be beneficial on a car with no rulebook to follow.

 

[blacksheep-1]

They were a big deal for a while back in the 80s with IMSA 962s and some Audis. I think they probably faded away because wheels are a consumable, and there were better ways to get the job done. If you just want an aero improvement old skool Moon Discs work fine and are much cheaper.