"VeloCat" <
[email protected]> wrote in message
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>
>
> Andy Coggan wrote:
> > "VeloCat" <
[email protected]> wrote in message
news:[email protected]...
> >
> >>Andy Coggan wrote:
> >>
> >>>Based on its Ksyrium-like profile, I suspect that the AC 420 wouldn't
be
> >>>much more aerodynamic than a standard box-section rim.
> >>>
> >>
> >>The Ksyrium rims are 24mm deep in cross section. The AC420s are 34mm. Why don't you think there
> >>would be a difference? The Zipp 303s are
> >>40mm. I would say the AC420 is more Zipp-like than Ksyrium-like.
> >
> >
> > Take a closer look:
> >
> >
http://www.amclassic.com/Rims.html
> >
> > Given the squared-off inner circumference, I can't see the extra 10 mm
of
> > depth being all that helpful.
> >
> > Andy Coggan
>
> While the Zipps have more of a bowed lateral surface, the inner circumference looks about as
> squared off as the American Classics. The only cross section I can find is:
>
>
http://www.zipp.com/Wheelsets/303_clincher.html
>
> I would think that there is some minimum flat area required for the spokes on the inner
> circumference.
I've looked at Zipp 303s, and own a Zipp 404 - there is no flat area like that found on the Kysrium
and AC 420 rims. (BTW, the "bowed" lateral surface of the Zipp is covered by a patent co-owned by
Hed and now Zipp, and is key to low drag when the wind comes at a slight angle).
As I responded to Michael Hoyt, there's more to rim aerodynamics than just depth, and I stand by my
prediction that the AC 420 is likely to more Kysrium-like than Zipp-like in its drag. (Kraig Willet
should be headed to the Texas A&M wind tunnel any day now...would be nice if we get an AC 420 wheel
to him to test.)
Andy Coggan