Here is the kart tire I hope to use. I would like to think a racing kart tire, known for running an excess of 130 mph, is any less appropriate than some trailer tire. But asking is the best course.
Also attached are three muffler choices for my wife's 250 Triumph. Straight pipe, open tube, shorty, and tunable cone. It would seem the tunable cone is the obvious choice but as is it chokes the flowed head.