With the increasing popularity of cyclocross in this country has come an increasing demand for knobby tubulars and large-diameter file-tread tubulars. This is because you can run tubulars at 25 or 30 psi without worrying about pinch flats. The rough courses and sideways loading generated by knobby tires really puts your gluing technique to the test. The minimal gluing that is adequate for riding a well-inflated tire on smooth surfaces will not do the job under these conditions, or any rough-terrain riding.
Brent