Many different factors affect how much weight a wheel can carry and every application is different. The "capacity" of a wheel to carry weight, or a wheel's ability to sustain a load will differ from application to application, and will depend greatly on;

• the variety of stresses and strains placed on the wheel
• in what direction loads are applied to the wheel
• how often loads are applied to the wheel
• how fast loads are applied to the wheel
• the manner in which a load is set against the wheel
• environmental rigours – temperatures, caustic mediums, etc.
• the speed at which a wheel is made to travel
• the number of wheels that will be used together to carry a load, and how they interact with one another

Users often ask "how much weight a wheel can hold"? The unique demands of every application make it difficult to provide a clear-cut answer, but rating systems have been developed to provide some insight. To give some idea of a wheel's suitability for an application, manufacturers and suppliers often discuss a "load rating" or "load capacity." Both terms are general and provide a basic description of the maximum amount of force that can safely be applied to a wheel in an ideal situation. A more definite term is safe working load (SWL).
Safe working load, sometimes referred to as normal working load, is the maximum weight that a manufacturer suggests a wheel can safely hold or transfer under ideal circumstances. It is calculated by determining the wheel's breaking point under a static load, and then dividing that number by an appropriate factor of safety. To help ensure jobsite safety and to mitigate its customers' risk, conservative factors are often applied when determining suggested SWL limits; determining the SWL requirement for an application requires an assessment by a competent person of the maximum load the wheel can sustain in the environment in which it will be used.
Not all applications are performed under ideal circumstances and wheels are often made to perform in hostile environments that may adversely affect a wheel's ability to bear weight. In these situations, it may be necessary to consult a professional. Some additional adverse factors that may indicate that a professional assessment is necessary include:

• a moist or damp environment
• abnormally hot or cold conditions
• any customizations to the dimensions of the wheel
• potential exposure to any chemicals
• speeds that will exceed 3 mph (4.82 kph)
• load that cannot be distributed evenly against the tread of the wheel
• multiple load or stress conditions; that is an operating environment where the wheel may be exposed to more than one type of load and/or more than one load direction