Experiment: smooth wheel discs tested A-B-A - 4.6% mpg improvement @ 65 mph

[Otto]

Hoerner's Fluid Dynamic Drag book is the bible for aerodynamics of aircraft, and has a section on various drag profiles of landing gear and wheels. Smoother is by far better, as seen in the tests noted above.

A few years ago, about 30 of us with Porsche 944 cars did a 500 mile ratrace through the interior of British Columbia, at speeds, ah, well above posted limits. The cars, being all 944s, had identical sheet metal and shape. Various wheels made a radical difference in slipstreams, as seen by the mist thrown out at high speeds on wet roads.

My car has Porsche Design 90 wheels, basically shaped on the outer surface like the pizza pan thing, but with vent slots forming 7 short, wide spokes out near the rim. Other cars had the whole range of Porsche and aftermarket more radically spoked wheels. My car had little visible wake, but the more radically spoked-wheel cars threw out a lateral column of mist ~3' out into the slipstream along the sides of the car. In other words, those radically spoked wheels, in effect, made frontal area of those cars about twice as wide, i.e, the hole punched in the ambient air was much bigger than the smooth-wheeled car.

As it happens, the disk-shaped wheel is likely to be lighter than a spoked wheel, and to have its mass closer to the center. This means less energy to accelerate and decelerate such a wheel, i.e., better fuel economy and braking on that account, too.

[Memorytwo]

why not just do what i'm gonna do, get some coroplast, cut it in a circle that fits the inner lip of the rim and zip tie them on the wheels.

i reccommend the black ties because they're more uv protected than the other colours.

and if you think 1 solid colour for the coroplast wheel covers is bland, get some spray paint out and stencils. I was going to try to put "ecomodder.com" with the logo on them. (once i can find coroplast, and the time to do it)

[Sean T.]

MY car came with a hubcap removal tool so HA!

Instead of an "X" shaped lug wrench, I have something similar to this:

http://www.debellajeepparts.com/LUG_WRENCH_SPECIAL.jpg

but with a flathead screwdriver-style end on the long side. It's curved just slightly, almost like a crow-bar.

I do have a question though... for those of you holding the pizza pan onto the center cover of your wheel, how do you get it off? Do you have to unscrew the pizza pan and completely remove the hardware?

I have a spare set of center caps for my new alloy wheels, but they are held on pretty tight to the wheel, so I know that if I bolted a pizza pan to them, I wouldn't be able to just pry the pizzapan off like a hubcap with the center cap attached.

[mobilerik]

Oh, hey! I never saw this thread. I did the Walmart pizza caps as well. I secured them with Zip ties after failing with every other idea. Right now I have no access to the valves, but I'll add a hole and valve extenders in the next few days. At under $4 a wheel, they're quite the bargain. I'm going to see if I can polish 'em up next weekend. By the way, they're not aluminum - they're steel, as my magnet accidentally discovered.

[NeilBlanchard]

Hello,

Here's an idea: take apart some old hard drives, and remove the (very strong!) magnets that drive the heads; glue the magnets to the wheels -- and stick the pizza pan/wheel covers to the wheels.

[Sean T.]

I don't think any magnet is strong enough to hold a pizza pan on while hitting a pothole at 40+mph.

[mobilerik]

Originally Posted by Sean T.

I don't think any magnet is strong enough to hold a pizza pan on while hitting a pothole at 40+mph.

I did try adhering the pizza caps with neodymium magnets, but the shape was wrong. Neodymiums can be made awfully strong. I had a hell of a time prying them off my rims. They're also cheap enough that you don't need to tear apart hard drives any more. Try magnets4less.com. They carry a safety warning - you can seriously injure yourself, as they'll readily leap a foot through the air to mate with another. Like some of us, I suppose.

And if one falls off... remember, we're talking about a $4 instant aerodynamic hubcap. If it falls off or gets stolen, then you go to Walmart and get another one!

[Christ]

HDD magnets are fun. You can make really old HDD magnets attract through a 1/2" thick oak table, which freaks people out, when something w/ a magnet hidden in it starts moving around on the table and no one is visibly manipulating it.

PC7 epoxy should be plenty strong enough to bond some magnets to either the rims, or to the pizza pans, and obviously, magnetism will do the rest. I'd say 3 decent HDD magnets, postitioned 72* apart, around the circumference of the wheel, would be more than sufficient to deal with everything except a pot-hole or a thief.

[DieselHybrid]

Look at what I stumbled upon:

Ferrari F1 F2008 | Formula 1 Photo Gallery

Look closely at the wheels. Can someone say "wheel covers?" Pretty nifty the way they painted them to look like their BBS sponsor's signature wheel pattern.

Open wheel racing is burdened by the enormous amount of drag generated by those large exposed wheels.

F1 gives them a toroidal shape and slaps covers on the ends. Presumably this lowers their drag.

However, if you look closely at the picture you'll notice that the covers don't spin- as evidenced by the vents.

Anyway... I thought I'd share.

[NeilBlanchard]

Hi,

My best guess as to how much smooth wheel covers (which are I bought from Hubcap Mike's) have helped my xA is: ~6.5%. It has been impressive.