A flat spot on your wheel tread can form when the wheel is loaded in a stationary position for extended periods of time. It is possible that the flat spot will disappear as the wheel begins to roll and take form again to it original state but this is not always the case. Whether the flat spot rolls out or is still present on the tread surface, having a flat spot will make moving the wheel from a stop more difficult. A polyurethane material’s tendency to flat-spot is determined by its compression set value. Choosing polyurethane with lower compression set values could solve the problem. Another approach is to use a wheel with a larger diameter or width, which reduces the stress on the urethane. This is also the same for soft rubber wheels. Soft rubber and polyurethane are the wheel materials where flat spotting most often occurs.
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 compounds can cause internal softening of the wheel’s material. When loaded, these soft areas may deform, forming a flat spot. A wheel with a flat spot may be hard to roll, and hard to push once in motion. If flat spots are a problem, consider replacement with a wheel material rated for the load, or one that will withstand the softening effects of liquids or chemicals.
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.