If you're ever wondering what rim sizes to get for your tyres then follow these simple guidlines:
For a 4.00x19 tyre, 4x18 tyre or any old 4" tyre, use a...
WM 2 rim
You can use a WM3 rim BUT the tyre will look a bit stretched and won't have the nice balloon look.
For me, the 4.00x18 tyres are perfectly proportioned, especially for a chop. The 4.50s are a bit too big and square on a zig zag Firestone. Maybe a Firestone ANS (with the lego tread) might look better in a 4.50. The ANS's also make an almighty squeal when you lock up the rear wheel.
For a 3.00" tyre, such as the common 21" avon speedmasters / on speed / pee masters..
..you should use a WM1 rim.
The WM2 will be too wide. This is on a WM1 and it looks perfect, I definitely wouldn't want a wider rim but different tyres may differ...
And yeah so what I wanted to show off my Grasshopper tyres again. But whatever you probably don't care because you don't have a trye fetish like me.
The Borranis were the first motorcycle parts I ever bought.