Recent posters are concerning themselves only with the RD's upper jockey wheel clearance for big cogs, while ignoring the cage length necessary to wrap large ranges between big and small cogs. You cannot use a short cage (or even medium) to shift 11-50T! Luckily, most folders aren't ridden in conditions where a long cage is in serious danger. The cage is running close to the rear wheel itself and may well be inside the overlap of a large section (~40mm+) clincher. I wouldn't worry about it. That said, I really wonder how necessary a 15" to 18" gear really is on a folder. The low gears of modern folders are getting ridiculously high in order to provide satisfactory top end. A 39T to 42T chaining used to be common on folders but they are now in the 50T plus! Anything that can be done to bring this down is admirable. I'd be chuffed to have a 22" low on my folder. I've learned much in this thread that I intend to further investigate. Grazie.