A hard wheel is often a solid material. Hard wheels will roll smoothly on smooth surfaces. A hard material is a good choice for smooth warehouse floors or hard floors that you do not mind getting marked or scratched. (I would not recommend using steel wheel on that new wood flooring in your house)
- Cast Iron
- Ductile Steel
- High-Temperature Glass Filled Nylon
A soft wheel is often made of 2 materials. The inner "core" material is usually a hard material and the "outer" material or "tread" is the soft material. There are some wheels that are made from a solid soft material. The benefit of using a soft tread is that it will roll more smoothly over debris that a hard wheel would get hung up on. A soft wheel is used often in hospitals and recording studios when rolling sensitive equipment around.
- Polyurethane on Cast Iron
- Polyurethane on Polyolefin
- Rubber on Caster Iron
- Polyurethane on Aluminum
- Solid Polyurethane
Imagine a Steel wheel being used on a cart that is being rolled down the sidewalk. Every crack in the sidewalk will provide an opportunity to stop your cart. The steel wheel will not absorb the impact, and the heavier the cart the more difficult it will be to roll over debris.
Now imagine a Soft Wheel in the same scenario. The Soft tread allows for the debris to be absorbed and the cart will likely be able to roll over it will little impact.
There are exceptions to these points, as with anything, but this is a safe rule to follow.