Showcase for Wheel Discs

[serialk11r]

Re rotors, on most cars I've seen the rotor's "intake" is on the far side of the wheel, so if you block off air from flowing out through the face, you're going to have hot air recirculating in the wheel well. The way I drive and most people around here drive, probably not an issue of course. But if you need the brakes I would guess that the cooling capacity is going to drop by a lot.

I've been looking at CFD pictures and I suspect that generally the spokes pushing air outward creates flow separation and thus reduced pressure recovery at the back of the car. Perhaps the Honda Insight/supercar rounded cutaway area behind the front wheels helps extract air from the far side of the wheel instead, and simultaneously helps air reattach along the side of the car. In high performance cars with brake ducts, the ducts go straight to the center of the rotor so it would be fine to have that air exhausting through the wheel well.

[rob.e]

I found this paper some time back on the aero / drag reduction of various wheel designs:

https://research.chalmers.se/publica...2_Fulltext.pdf



Looks like the basic flat cover isn't necessarily the best option.

The "thick outer radius cover" performs the best according to this research - probably why ABT use this sort of design on their formula e car and RS4: i posted about that wheel here but no one responded

https://ecomodder.com/forum/showthre...hts-37743.html

I'm thinking of trying out something like this on mine.

[teoman]

Looks like an interesting mod. Considering the outer edges are the fastest moving part, it should be the most benefiticial.

[teoman]

My car has an inward fan design. So maybe covering could prove to be a negative effect.

[Daox]

Originally Posted by rob.e

I found this paper some time back on the aero / drag reduction of various wheel designs:

https://research.chalmers.se/publica...2_Fulltext.pdf



Looks like the basic flat cover isn't necessarily the best option.

The "thick outer radius cover" performs the best according to this research - probably why ABT use this sort of design on their formula e car and RS4: i posted about that wheel here but no one responded

https://ecomodder.com/forum/showthre...hts-37743.html

I'm thinking of trying out something like this on mine.

I think you're reading the wrong chart. Figure 10 is about ventilation resistance. You want to look at figure 12 - "Percentage difference in aerodynamic drag for different configurations". This shows a full cover is the best. Though, there are a couple that are close behind it.

[rob.e]

P6

"As expected fully covered wheel shows good results, but as it can
be seen thick outer radial cover actually performs better throughout all velocity range"

P8 conclusions:

"..rims with large outer radial cover were known to perform well in terms of aerodynamic drag force. They have been proven to be good in regards ventilation resistance as well. Moreover having a rim with thick outer radius cover was proven to be more efficient then having a fully covered wheel."

[California98Civic]

Wow. Cool article. On a different point, the authors also make this surprising claim:

"As it has been previously investigated when the wheel starts to
rotate there is an expansion in the tire due to inertia [6]. This
expansion changes the tire shape, see Figure 6, and affects the
rolling resistance. The tire radius may change by as much as
8mm, depending on the material properties, weight of the
vehicle and speed. For the set-up used during the test the
maximum tire expansion measured was 2.5 mm for the
velocity of 200 km/hour."

8 mm would be a quarter inch and 2.5 a tenth of an inch. Not insignificant, though not huge, either.

EDIT: Back to the main point of this discussion for a second, it seems figure 13 is the most important in the article as it takes into account both ventilation drag and aerodynamic drag for a calculated total figure. Here's that graph:



2CD EDIT: (don't hate me for all these edits, lol)... rim configurations.





ARTICLE AUTHOR'S PREFERED CITATION:
Vdovin, A., Bonitz, S., Landström, C. et al (2013)
Investigation of Wheel Ventilation-Drag using a Modular Wheel Design Concept
SAE International Journal of Passenger Cars - Mechanical Systems, 6(1): 308-315.

[freebeard]

On a different point, the authors also make this surprising claim:

If you see an AA-Fuel dragster heating up the tires before the starting line, they grow by 2-3 inches.

[California98Civic]

Originally Posted by rob.e

... a rim with thick outer radius cover was proven to be more efficient then having a fully covered wheel."

The difference between the thick outer radius rim and the fully cover Grimm is so modest, however, that I have to think this result might turn out to vary a little bit according to the car and the shape and design of the wheel well that needs to be ventilated.

[rob.e]

Originally Posted by California98Civic

The difference between the thick outer radius rim and the fully cover Grimm is so modest, however, that I have to think this result might turn out to vary a little bit according to the car and the shape and design of the wheel well that needs to be ventilated.

agree 100% difference will be modest - one positive for me with not having the wheel fully covered is that you can more easily access the lugs for wheel removal, and having some ventilation will help with brake cooling.

i'm going to make a start on mine shortly... and a grille block