Illustrating Jon's comment my 13" MotoLita has a nominal diameter (core of rim) only a little greater than 12". Suits my power assisted Roadster perfectly though and doesn't look too small IMO.

[Linked Image]

This is the thick rim version BTW which I recommend.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone