The TART is small bike friendly. There are sections near Lake Winona and in the Weyerhauser Forests that would present problems for anything larger than 650.
JoeNuclear did the TART with his XRL however, he is an accomplished rider and his bike is set up for it. There are some long sections of pavement on the TART due to lack of adjacent gravel or trails and rivers without crossings. But, the paved sections (which were unpaved three years ago) are nice and twisty so it makes up for being paved.
Damn Gubermint is screwing with roads by paving them...ack For those who are interested in tying the Missouri trail into the TART you will find routes and tracks HERE