Carpet means HARD WHEELS!
Picking the right wheel material for your type of floor is very important. Casters with Hard Wheels will slide on a hard floor like ceramic tile or hard wood. When they slide, they can scratch the wood and on tile the wheels can actually be "sanded" down a they slide over the grout lines. This leaves bits of black plastic on the floor. Hard wheel casters work best directly on carpet. For short pile carpet, a 2" or 50mm wheel will work fine. For deeper pile, a larger wheel of 60mm or 75mm is needed. If the pile and padding is very deep, use a floor mat; a FLOOR MAT is HARD and needs Soft Wheels.
Tile and Wood means SOFT WHEELS!
Casters with Soft Wheels can get "traction" on a hard surface. Just like the rubber tires on your car, caster wheels will have some sort of soft material applied to a wheel. When a wheel is rolling on a hard floor, it can not scratch the floor. Hard floors can get damaged even with soft wheels. If the floors are dirty and grit or sand becomes embedded into the tire, it can scratch the floor. If the wood used on the floor is soft, it is possible that the wheel could "dent" the wood. We will not "recommend" any type of caster for a wood floor. We can tell you that the "softest wheel" will work the best. A good rule of thumb is that if you have a wood floor, find out what the Janka Rating is for the floor. If the Janka rating is higher than 1290 ( the hardness of solid Red Oak ), you should be able to use wheels with soft polyurethane wheels. If it is softer than that, you must use a soft rubber.
Watch the CAPACITY OF THE CASTERS!
Casters are rated by how much weight they can hold. That doesn't mean that they will roll well with that much weight as there are many factors that affect how it rolls. Too much weight on a caster with a small capacity is not safe. Under normal conditions, when you figure capacities, you multiply the capacity of each caster times the number of casters used. This will give you the maximum weight that can be held by this set of casters. This is true for furniture as long as the weight is equally distributed but if it is not, add more casters to the heavy end to try to balance the load. CHAIRS are another issue with capacity. When you sit in a chair and don't move, your weight is fairly balanced on the casters. As you try to roll, you shift your weight and now some of the casters are carrying more weight. The worst part is when you lean back or lean forward. It is possible that ALL of your weight is transferred to the front 2 casters instead of 5. The maximum capacity for chairs should never be more than 3/4 of the total capacity of all the casters. Please think SAFETY when putting casters on a chair.