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Old 08-17-2006, 04:47 PM   #1
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Do smooth hubcaps (for example, a "Baby Moon") help with FE? Has anyone tried it? If so, how much did it help?

This seems to me like it might be one of the easiest aerodynamic mods to make (since you just buy the hubcaps, and put them on). And it is pretty cheap to buy a set of hubcaps. But does this help? My thinking says it could go either way:

1) It might hurt FE, because the wheel covers will weigh something, and this will (slightly) raise the weight the wheel has to turn. OTOH this added weight isn't that high (especially compared to the weight of the tire and wheel itself).

2) OTOH it might help FE, because smooth hubcaps should make the wheels more aerodynamic, by covering over the places the air can get trapped in.

Either way, this mod should be reasonably cheap and easy to do (just buy a set of hubcaps, and put them on). And unlike some aerodynamic mods, this one isn't likely to draw a lot of attention to itself (as many people snap hubcaps on their wheels). And it should even cover up the rust on the wheels themselves.

But has anyone tried this (and if so, how well did it work)?

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Old 08-17-2006, 04:57 PM   #2
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See this thread.

On a side note I am kicking around putting them on my Yaris.

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Old 08-17-2006, 04:57 PM   #3
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Somebody just did full moons...even had pics.
Leading the perpetually ignorant and uninformed into the light of scientific knowledge. Did I really say that?

a new policy....I intend to ignore the nescient...a waste of time and energy.
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Old 08-17-2006, 04:59 PM   #4
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As a general rule of thumb, I think aerodynamics > weight for FE.

One of the newer members just did this actually, but I haven't seen any results yet:

I say go for it. Basjoos has done it as well. Other people I'm forgetting at the moment, sorry guys/gals!

Edit: Damn, I got pwned.
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Old 08-17-2006, 05:25 PM   #5
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My wheel covers are also smooth, but they don't necessarily look it in the photos due to my awesome fabricating skills.

Some actual figures to chew on:
Indeed by completely sealing all four rims, Cd can be reduced by 0.08 to 0.012 (ref. 6). The maximum drag difference between a good and a poor set of rims is probably even larger.
Source: Contribution of different devices to the total drag

There's a section in that report devoted specifically to wheels, rims and wheel housings.

Edit: my wheel covers were pretty well designed to begin with, so my gain is likely on the small end of the scale (and further reduced by the rear wheel skirts). Small enough that I haven't tested it, and probably won't bother.

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Old 08-17-2006, 06:03 PM   #6
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Once I get my 14 inch tires (Ahem Bunger) and LRR Insight tires, I'll get some smooth hubcaps too... why not?
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Old 08-17-2006, 07:57 PM   #7
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I'm working on my first full tank with the moon caps installed... I'm only about 200 miles into the tank, and I'll be out of town for the next two weeks after I get off work Friday morning so I won't have data to share for awhile (unless I decide to fillup on my way home - but I hate short-tanking).

No promises, but my SG tank MPG reading is showing a tad higher than my last tank of 50.16MPG, which was a personal best.

No issues with brake temps, but the darned things are noisy at slow speeds!
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Old 08-17-2006, 09:22 PM   #8
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I rather question my vx rims at times because of my expearince with bicycle wheel airodinamics, the spokes of a bicycle wheel work alot like an egg beater, each spoke stiring up the air, thus the justifide demand for blade like bicycle spokes for racing, and me left wondering how good the 8 spoke vx rims really are, so it makes sence that the hybrid civic has wide flat spokes, and the insight has near disk rims with smal vents around the outer edges, so the worst rims you can get, airodinamic wise would be the ever so popular thin spoke large diamiter alloy rims (the spokes look thin, but are really wide flat blades, like a whole bunch of little fan blades...
We just got some of the spun alluminum Moon hub caps for the metro, but we haven't owned it long enough to have a solid feel of the mileage, nor do we have a scangauge yet and I haven't taken the time to find out what they weigh, but I'm sure I'll do it at some point.
either way, unless you get some heavy stainless steel caps or something crazy like that, smooth caps should help.
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Old 08-18-2006, 02:35 AM   #9
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I noticed the water spray out of the rear wheel well of other cars on Tuesday highway trip and it seems that a lot of spray comes off the top of the tire blowing forward and then out of the top of the wheel well. That has got to be wasting power. I think a layer of clear shrink wrap over my hubcaps will have some effect - need to find a wide piece - I think I have some from a laser toner cartridge shipment that should be wide enough - pop off the caps wrap and pop them back on.
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Old 09-09-2006, 09:38 PM   #10
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I have had the snap-in baby moons. They are gorgeous but they fly off in a good bump (always my front passenger rim, maybe it's a front wheel drive physics thing particular to my previous Saturn coupe). The "real" baby moons that you see on hot rods are screwed onto the wheel rim.

How about the "floating hubcaps" that are on Taxis? I have a bunch of URLs but none of them look exactly like the ones I have seen in Los Angeles. Also, it doesn't look they are offered retail. You need to buy them in mass. Finally, they are not "flush", there is a gap between the tire rim and the floating hubcap, or the circumference is slotted, so I don't know if that negates the benefits of the flat hubcap (the ones in LA do look cool, though). (in French)

Old School SW2 EPA ... New School Civic EPA :

What's your EPA MPG?
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