Hi, Edward,
Sorry I've taken a while to respond, but like you I've been searching through my bookshelves and magazine piles for that article I just knew I had seen somewhere. Well, I finally found it in a Japanese magazine. The only bit I could read was the following list of rim/tyre sizes.
1. A 1.20 rim fits 2.25 section tyres.
2. A 1.40 rim fits 2.50 section tyres.
3. A 1.60 rim fits 2.75 and 3.00 section tyres.
4. A 1.85 rim fits 3.50 and 4.00 section tyres.
Be aware also that the angle of the spoke holes varies according to the size of the hub. If you lace a rim designed for a disc braked wheel onto a big drum brake, the spokes will acquire a definite bend at the rim end - probably not a good idea unless you're desparate.
The BS175 uses 1.60x18 rims front and rear, but the Dual Twin's 2.50x18 tire does look a bit small on that rim. It rides OK, but looks wrong. I've settled on a 2.75x18 front trye and 3.00x18 rear on my DT and the slightly fatter tyres look better at both ends. The 175HS and 200SS use (I think) 300x18 tires as standard which fit the rims perfectly.
I've confirmed some of these sizes by looking at the original "Takasago" rims on my Suzukis. These cleverly have the sizes stamped on them. Bridgestone used "DID" rims which have no such markings!
Hope that helps.
Graham
