I wouldn't do bike teaching in a gym, because if/when the bike falls over, the pedal, or handlebars, or axle, will gouge the expensive varnished wood floor. Some gyms have rubbery floors, better, provided nothing will slice that. If you must teach inside, pad all places on the bike that could impact the floor. Also, the wood floor is smooth enough that the tire can slip out in a hard turn, most especially if a drop of any liquid, like sweat, is on the floor.