A flat spot on your wheel tread can form when the wheel is loaded in a stationary position for extended periods of time. Soft rubber and polyurethane are the wheel materials where flat spotting most often occurs. There is a chance that the flat spot can disappear as the wheel begins to roll and take its true form again back to its original state but this does not always happen. Whether the flat spot rolls out or is still present on the tread surface, having a flat spot will make moving the wheel into a roll from a stop much more difficult. A polyurethane material’s tendency to flat-spot is determined by its compression set value so choosing a polyurethane with a lower compression set value could solve your problem. Another approach is to use a wheel with a larger diameter or width which reduces the stress on the urethane.
Wheels can develop flat spots on their tread due to a variety of causes. Heavily loaded polyurethane wheels that are stationary for long periods of time can develop flat spots. Heat buildup in polyurethane, or interaction with liquids or chemicals in some wheel compounds can cause internal softening of the wheel’s material. When loaded, these soft areas can then deform which will cause them to form a flat spot. A wheel with a flat spot may be hard to roll and hard to push once in motion.
Another issue that can cause a flat spot on many wheel materials is sheering. Often times people roll carts into place and then push the rigid casters sideways to “stack” their carts in line for storage. This sideways sliding for on the wheel can break down any wheel material and cause flat spots all around the tread. There is no real fix for this last issue other than working with one of our professionals to try and structure your storage process in a way where the sideways pushing is not necessary. Otherwise these wheel flat spots may be unavoidable.