Originally Posted by
noglider
I'm sure that's correct. There was a gear that meshed into that ring, which spun a cable which ran to the speedometer/odometer mounted to the handlebar.
You can see it in the pic, the white cable has the little gear on it.
This is a cool bike. I know there's a distributor in Canada (babac) that sells 571mm tires too but I would imagine they are the same CST tires you found. A friend has an old CCM that has the same tires and they were the only ones I could find in that size that are anything close to balloon tires.