Classes generally use specialized stationary bicycles. Features include a mechanical device to modify the difficulty of pedaling, specially shaped handlebars, and multiple adjustment points to fit the bicycle to a range of riders. Many have a weighted flywheel, which simulates the effects of inertia and momentum when riding a real bicycle. The pedals are equipped with toe clips as on sports bicycles to allow one foot to pull up when the other is pushing down. They may alternatively have clipless receptacles for use with cleated cycling shoes. Padded shorts aid comfort and avoid the chafing caused by the sewn seams in underwear.