What you were seeing is not actually a spoke cover - I can see easily how it
looks like one. It is actually a totally different designed wheel called a
disc wheel.

The two common places to find them are time trials and velodromes (indoor
bike tracks).

Here's a few notes on them from Sheldon Brown's web page (an excellent
resource for many things in cycling)

http://www.sheldonbrown.com/home.html

Disc wheel
A disc wheel is a wheel with solid sides, instead of spokes. Although disc
wheels are heavier than spoked wheels, they have less air resistance, and
permit a cyclist to go noticeably faster. They are not usually used on the
front, because they can cause severe handling problems in cross winds. They
are not usually used for hilly conditions, because the added weight is too
much of a disadvantage on the climbs.
The illustration is from Archibald Sharp's Bicyles and Tricycles, originally
published in 1896, reprinted by the M.I.T. Press in 1977.

The front wheel has cutouts to reduce steering problems that result from
crosswinds when disc wheels are used on the front.


Bruce





>From: "bmkr94" <bmkr94@...>
>Reply-To: tourofthesciotorivervalley@yahoogroups.com
>To: tourofthesciotorivervalley@yahoogroups.com
>Subject: [TOSRV] Wheel Spoke Cover
>Date: Fri, 03 Aug 2007 08:00:12 -0000
>
>During the tour time stages, I observed some riders whose bikes had a
>center wheel spoke cover mounted on the rear wheel and not the front.
>If not being used on both front and rear wheels, what benefit, if any,
>are covers on just the rear wheel? In some cases the bikes with a
>cover on the rear were using what appeared to be a carbon, 3 spoke,
>aero front wheel.
>
>Use of wheel covers raises some question about the material used and
>any build up of static forces that could react to rotational motion of
>the wheel that might impact the bike. For example, magnetic plate
>stationary bike trainers, these use magnetic plates to generate an
>opposing force between magnetic plates, causing rear wheel resistance,
>causing extra force to combat resistance at the pedal crank.
>
>Yes, I know the latter is a stretch but, it is 4:00 AM as I write this.
>
>

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