If you define aero as a high aspect ratio and a curved profile I would go with the Conloy Asps as an early example. These are such a nice alloy rim, first available in the mid 1930's. After production of these rims stopped (mid 50's?) I doubt if there was a clincher rim available to equal them for 20 years.
Great Notch, NJ
> My 1878 Rudge has what could be considered aero rims. They are box
\r?\n> section with the profile height being greater than the width.
\r?\n> I'm sure that others predate the Rudge in this respect.
\r?\n> Steven Maasland
\r?\n> Moorestown, NJ