The larger the curved surface area of the wheel, the easier it rolls on all surfaces (due to the reduction of pressure). On smooth surfaces hard treads roll the easiest, but consider potential floor damage on rough or soft surfaces, where soft treads roll easiest.
In theory a wheel transfers its load to a hard floor along a line of contact. In practice this is an elongated area which is - Narrow for Cast Iron wheels, wide for Polyurethane wheels and widest for Rubber wheels. On smooth, hard surfaces a cast iron wheel with a narrow contact area may roll more easily, but its unit load will be very high. The unit load (crushing pressure) is the total load divided by the area of contact. If this pressure is too high it will damage the floor. In practice the crushing pressure of cast iron wheel will often exceed the compressive strength of concrete, particularly when the load is further concentrated at expansion gaps, cracks etc., or when the loads are increased by speed and inertia. In practice cast iron is recommend for towed use. Polyurethane spreads the load sufficiently to avoid damage to floors, without a large increase in the ‘push’ necessary. Its great resilience and abrasion resistance makes it an ideal material. It also cushions the load, and avoids damage to the castor and trolley. The concrete floor of any warehouse or factory must be protected from damage by choosing the appropriate REXELLO CASTORS & WHEELS. Rubber wheels, although popular, are too hard to push at high loadings and can get adversely affected by oils, chemicals, etc., and they last only 1/5 (or less) the life of polyurethane wheels.