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We are surrounded by a plethora of solid-spoked alloy wheels on motor vehicles. These are expensive to make and buy, but there seems to be minimal aerodynamic attention in the design process, particularly to the all-important shape of the spokes. Wheel manufacturers give no thought to this at all -
it's full speed ahead, maximum bling-bling and gratuitous über-chrome everywhere.
Since the patch of wheel touching the road is always stationary, the top of the wheel is actually moving forward at twice the vehicle velocity. Drag is of course a high order function of velocity.
It would seem that a modicum of CFD design engineering should be done to shape the spoke and spoke/rim interface to reduce drag at this high-velocity point where it's most critical. This could increase your Ford Excretion's fuel efficiency from its 7.5mpg by at least 19ipg (inches per gallon).
"Moon" wheel covers
http://www.autoznet.com/Moon.jpg
[half, Oct 04 2004, last modified Oct 05 2004]
Honda Insight wheel
http://images.autob...k_2_x_exwheel_x.jpg
"Low drag" wheels on a Honda Insight hybrid car [discontinuuity, May 31 2006]
[link]
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This is a big deal with bicycles. |
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How much of an automobiles wheel is actually causing drag (as opposed to the tire)? |
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Would a set of good old-fashioned "moon" hubcaps do the job? |
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The Nissan/Renaut GTR35 concept uses the spokes as fans to cool the brakes...kind of related... |
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//The Nissan/Renaut GTR35 concept uses the spokes as fans to cool the brakes...kind of related...// |
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Which ties into my "Thermally-controlled hubcap" idea. Why blow air over brakes to cool them if/when they aren't even warm? |
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[supercat] to help reduce brake dust and other junk? I know my Ford F-150's rims have ports on them to direct air on the brakes and back. |
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oh, and *Excursion not Excretion |
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Fashion the wheel spokes into turbine blades to evacuate the air from under the body. You'd have to have "directional" wheels. |
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"Wheel manufacturers give no thought to this at all."
What makes you think that? Wheels have to provide cooling for the brakes, plus have minimum drag and more importantly, low inertia to allow for acceleration. On top of all that, they must be designed for consistent behaviour when they are being cast, plus minimum machining afterwards. To suggest that they're just drawn on a computer somewhere and then mass-produced is a little off the mark. |
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The point of spoke wheels is to be cool, not to save gas. Same with spinners. |
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The point of wheels, at least how I see it, is to give something upon which to mount tires. |
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The purpose of spinners is to look foolish. |
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What do the F1 folk do for wheels? I'd think they'd be the people to put the most effort into all-around efficient wheel design save maybe the Indy folks (or the land speed record guys). |
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I used to draw cars all the time (almost failed trig because of it), and was struck by the lack of air control under vehicles: in through the radiator, then who cares where it goes? There's only one place: underneath. That's why I liked our old SAAB with its full flat bodypan and no greeblies in the wind.
Give the spokes a profile that gives them a positive effect, drawing air out from under the vehicle. This should increase downpressure a tiny bit for better roadholding, and cool the brakes too. |
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[david_scothern], there's a difference between FEA (finite element analysis, primarily used here for structural analysis) and CFD (computational fluid dynamics). They'll check to make sure that the rims are strong, safe, and easily manufactured, but style is far more important than aerodynamics because style sells to morons with more money than brains. |
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I believe the Honda Insight has wheels
made with aerodynamics in mind, or at
least wheels made to look aerodynamic
(see link). |
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I dont think this is really a big issue for automobile wheels, as they are generally burried inside a fender and the big aerodynamic zones are at the nose and over the roof. The comments on racing technology are very valid here. All racing formats pretty much do not use special aerodynamic wheels with the exception of Land Speed vehicles and bicycle racing for time trials. Ithink the benfit is of limited if not no value at all. |
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