You can go up to a 180 mm wide on your stock rear rim, not a lot of tire selection to pick from at that width. If you want a 200mm rear, then the easiest route is a 5.5" rim laced to a spoker America hub. With a 200mm wide tire you get close to 5/32nds" tire to chain clearance, any wider than 200 and you will need to shim out both sprockets and do some relief trimming on your chainguard. This the best deal around on a wide rear rim going:
5.5_40H I called Devon rim service in the UK first, as I wanted to stay with a 15" diameter and for $695 plus some obscene shipping costs, he would provide me with a 5.5 x 15" Stainless rim, so opting for the Buchanan rim was a no brainer, cost wise. Besides, a 200/80-16 Avon Venom looks the stuff and handles great.
