Well, got curious, went out to the shed and measured the external width of my Weinmanns. 19.2 or something. I'm thinking I should be good with the superlite's 18mm external width. But, I'd love to hear about someone else's experience with these wheels and larger tires.
Also, there is a graph at this link what also answers my questions
THE RIGHT TYRE WIDTH ON THE RIGHT RIM WIDTH - Engineerstalk : Engineerstalk