Hi Craizie
I was just Googling "Ariel Cycling Club" when I stumbled across your post. though it looks as though I'm about 3 years late in replying! My great grandfather was a member of the club (which was a bicycling club and not a motorcycling club).
I have in my possession a bound copy of 'The Ariel Gazette' (the club magazine) which covers the period May 1893 to March 1894, and it certainly contains some references to your great great uncle.
Attached are a couple of images which I hope will be of interest. The first is an advertisement:

it looks as though your great great uncle was the proprietor of a bicycle shop.
The second is a short piece about William E. Prust:

Chris