Of course there is a site dedicated to the various motorcycles used by Henry Winkler as Arthur Fonzerelli / The Fonz / Fonzie on Happy Days. Fun fact, he couldn't ride a motorcycle, never could, and didn't. Actually that page part of a larger site dedicated to the first 3 seasons... the cool ones... of Happy Days.
The second bike was the most used, a silver painted Triumph TR5. The actual one below.
Sidenote: wasn't his apartment over the garage the jam? It even spawned a phrase in real estate; the Fonzie flat.