Thank you, JohnF3 and all. Lots of cheerful help, here!
In comparison, I posted the same question in the Husaberg section of Thumper Talk and didn't get a single response.
Thanks to all!
Well, this is a very late reply but for future info, I put the 140/80-18 MT21 on my 570S with no problems. I do like these tires especially for their good manners on road. I will buy them again but I want the try the Kenda K760 Trakmasters just out of curiosity.