Better wheel covers than 'smooth'?

[aerohead]

*going over the paper,it looks like only 'flat' discs were investigated.
*convex discs (MOONs) have lower drag than flat discs (I'll have to did for that data)
*when the Spirit of Ecomodder.com video is available,you'll be able to see the turbulence within the tire sidewall bulge-generated void, present with a flat cover,but mostly eliminated with the MOON-type cover.

[freebeard]

The best treatment I've seen. The wheel rim appears to be 1-2" inside the circumference of the cover, inside and out. And wide compared to the tread width.

There was a Mariani Farms car on the Salt this year, but it wasn't nearly this slick. When I asked about it, they said "Oh, that's probably my brother."

[Madact]

Originally Posted by Cd

Am I missing something ? I read this as meaning that a fully covered wheel is best for low drag :

" Also, as predicted, the Fully covered rim design produced the lowest aerodynamic resistance, closely followed by the Thick outer radius cover."

The paper defines the term "aerodynamic resistance" as the linear drag acting on the car due to air flowing past it, and "ventilation resistance" as the force retarding the rotation of the wheels due to the way they move air in the wheel housing and between the wheel housing and the outside of the car. Obviously, for efficiency purposes we want the total energy cost of the wheel design, so they sum the two for the overall result.

[Madact]

Originally Posted by aerohead

*going over the paper,it looks like only 'flat' discs were investigated.
*convex discs (MOONs) have lower drag than flat discs (I'll have to did for that data)
*when the Spirit of Ecomodder.com video is available,you'll be able to see the turbulence within the tire sidewall bulge-generated void, present with a flat cover,but mostly eliminated with the MOON-type cover.

Interesting - any idea how much better the moon covers are? It sounds like it could be quite significant...

Of course, that still leaves open the question of whether moons with holes (or even just one smallish hole, in the middle) to reduce ventilation resistance might perform even better - quite likely not, of course, if the hole mucks up the attached flow, but if only a small region of the airflow was affected, it might. Oh for a personal wind tunnel

Originally Posted by freebeard

The best treatment I've seen. The wheel rim appears to be 1-2" inside the circumference of the cover, inside and out. And wide compared to the tread width.

Very nice - I've thought about covers which are wider than the rim, I'm a bit leery of trying to apply that to a daily driver though... I don't like the idea of the sidewall rubbing on stuff

[Madact]

Originally Posted by aerohead

*convex discs (MOONs) have lower drag than flat discs (I'll have to did for that data)

BTW, if you find that data, I'd be extremely interested to know *how much* convexity is optimal... I presume the minimum which eliminates the turbulence, but how much that is would be useful to know. Not an easy thing to tuft-test... though I am working on a smoke generator / smoke wand, which could be useful.

[freebeard]

I don't like the idea of the sidewall rubbing on stuff

I hear that when the subject comes up. 1/4" gap couldn't hurt.

IMHO it wouldn't rub; more of a press and release. Notably at the bottom where the tread will flex. If the rim is wider than the tread it braces the sidewall to increase what's called 'turn-in' and reduce sidewall flexing. A soft wide tire on a narrow rim can be rolled right off in hard cornering. The hubcaps tend to go first.

Not an easy thing to tuft-test... though I am working on a smoke generator / smoke wand, which could be useful.

Put 'smoke' in the search field. Personally, I like to drive on the freeway in a heavy rain and observe the forward-rolling outward-expanding spray; and how it varies from vehicle to vehicle.Since the water particles have more mass than air, you can read them like vectors in a CFD diagram.

[Madact]

Originally Posted by freebeard

Put 'smoke' in the search field.

Have done - going the propylene glycol route, it's easily controllable, and as far as I can tell completely safe (provided you aren't breathing directly from the smoke output )...

[COcyclist]

I couldn't get the link to work just now. Hmmm.

I have tried flat coroplast covers on my VW Golf and they didn't help and may have hurt my tank averages compared to the alloy 9 spoke summer wheels. Sorry, no true A-B-A testing though.

[NeilBlanchard]

These look pretty sweet, as well:

[Madact]

They look sweet indeed, and appear to be vented in the middle. Apparently they have a website http://www.mooncraft.jp/ though it looks like they're a racing company, rather than selling on to the public :-/