However, on deep pile carpeting, very soft padding or chair mats, soft wheels which are resilient and give, provide a better and safer ride. They can harm the mat or hard floor surfaces. Just as tires must have the proper tread for safe driving on dry pavement as well as slick or snow covered roadways, chair movement depends on wheels that provide appropriate traction on hard or soft wheels. Caster wheels that are incorrect for the floor surface can pose risk of serious injury. Hard floor surfaces require soft wheel casters to prevent dangerously rapid movement while user is seated or rolling away, when user rises, or when user bumps empty chair causing it to move out from under user.
Muscle strain can also result due to the users effort to keep chair in place.
Hard wheel casters are necessary for carpeted surfaces as they allow the chair to glide smoothly over carpeted surfaces. Soft wheel casters used on carpeting can also cause muscle strain due to the increased difficulty in making chair move. Then it is a soft wheel. A hard wheel would not have any resilience. No, some caster manufacturers use round tops, some flat - makes no difference.