On my 1971 Camaro the side windows are frameless, that being said I took the initiative to replace rollers, channel felt, and other various things and adjustment to make my window fit tight. No problems to dang near 260. Also a lexan window can blow out of the car too, thus upsetting car aero and handling. What ever happened to racers making sure their equipment is up to standards and thus eliminating rules for every situation that could happen? Just a thought.