VW Hub Caps

[hardingfv32-1]

As stated from the manifold thread:

"Not to go off topic, but for those who are viewing this issue (manifolds) with concern about the class, check over at ApexSpeed.
The FF guys are debating new wheels at maybe $2400 a SET!"

Could these FF wheels be the new aero flush surface type? They do make a difference.

Could we run stock VW hub caps if a mounting system could be developed since the hub cap clips are not allowed?

Brian

[Matt King]

Moon discs.

[hardingfv32-1]

Yes ..... Moon Discs

With special lug nuts (free hardware) that you screw the flat head mounting screws into.

Brian

[Bill_Bonow]

That was pretty much exactly what had been done here in CenDiv in the late '80's by Rich Sharpe in a Citation. Looked really cool, but he claimed it was a real pain to change wheels. He got away with it for an event or two before tech made him take them off. He argued free hardware and ridgid attachment, but in the end he took them off.

Hey, but that was around 20 years ago. Most of those tech guys are pushing up daises by this point. I say bolt 'em up. Besides, I'm still waiting to see that offset front wing you're going to build.

[billinstuart]

The first Caracal D I saw had an airfoil in front of the rear tires.

[Bill_Bonow]

Bill,

Now that one I have a photo of, but I've been digging around trying to find it.... no luck. My photo was of Kerry Bowman's spotless yellow D car at Road America around '81 or '82 (when D cars were truely skinny). They were pods/pontoons that hung "on-a-stick" in front of the rear tire. Most guys put their car number on them to prove they were bodywork. Same deal, lots of controversy. Most of the fast guys took them off. Not because they had to, but because the car went faster without them.

This was in the great FV era of "basket handles, tabs and epaulets". Ah yes, the good old days.

[Bill_Bonow]

I couldn't find it the first time I looked, but in the GCR under 9.3.10. "hub caps must be removed in all classes". Once I read this, I remembered Rich Sharpe's argument, that they were not hub caps but in fact they were valve stem protectors and in his veiw, a safety item.

[hardingfv32-1]

Well, this was worth posting. Was not aware of the GCR hubcap rule. End of subject, no grey here.

Are the new FF wheels in fact smooth surface aero types?

Offset front body work will have to wait until next year. Will be tied up at Monster Manies getting other competitors ready for the Runoffs.

Brian

[Bill_Bonow]

Are the new FF wheels in fact smooth surface aero types?

Brian,

You tell me.

[ external image ]

They are (4) piece monocoque wheels made of spun sheet aluminum with inner/outer hats and inner/outer centers.

IMO, if they have an advantange, it has more to do with minimizing rotating weight than aero. But hey, for only $2,400 per set, you can get the best of both worlds

[dd46637]

I do believe the initial advantage was almost all psychological judging by the uproar on apexspeed. 9 page thread and still going

[Mad Dog Racing]

I thought "hub caps" were the metal covers on the front brake drums that cover the spindle nuts. You know, the ones that get knocked off when you don't give a full car width and two coats of paint in a corner.

(I know, common term for wheel covers is "hub caps", for those of us of a certain age.)

[hardingfv32-1]

I have a aero study that shows these Moon Discs work.

The wheels are 65% of the aero drag for a Vee, I would estimate the number at 75% for FF with wider wheels and sleeker bodies.
Could be at least 40% of FF HP going to move the wheels through the air. Would not take much to save 2-3 HP. Don't ask your engine builder for such a gain.

Brian
hardingfv32@verizon.net

[nick_fv71]

This may be a dumb question, but isn't the majority of drag from the wheels due to the frontal area and therefore the aero effect of smooth wheels on a FV at our slow speed would be negligible?

[hardingfv32-1]

The drag is a function of Fa (frontal area) X Cd (drag coefficient). In the case of the Moon Discs we are trying to improve the Cd part of the formula. Yes, the shape of the front of the wheel is terrible, but this is a system with a front, middle, and rear. The Cd will be improved a little if the air flow is kept out of the wheel interior.

Yes, the improvement in a Vee would be hard to detect, but the FF is a little different.

Brian

[Matt King]

A Hub Cap is specifically defined in the GCR as being a "decorative" cover, so if it has an aerodynamic purpose, which is functional, a Moon disc should be legal since it is not expressly prohibited in the FV rules like it is in the FF rules. I think they would look cool on my XTC! Ooops, that would make them decorative. So I think they would make my XTC more aerodynamic, and protect the valvestems and wheel weights.

[FVartist]

A grease or dust cap covers the wheel bearing and a hub cap covers the wheel rim or lug nuts.