Radial Load Basics

Along with torque overloading and shock loading, excessive radial loading (overhang load) is one of the top reasons gearboxes fail. It is also one of the least considered elements when integrating speed reducers with gear, belt, and sprocket drive systems.

A radial load, or overhung load (OHL) as it is also called, is a bending force imposed on a shaft due to the torque transmitted by belt drives, chain drives, or gears. Radial forces can also be created by belt or chain tension and by a misaligned shaft coupling.

While shaft size is a consideration, it is the type, size, and center distance of the bearing system that most determines radial load capacity. Other elements that affect capacity are the rotational speed, the load distance from the bearing, and to a lesser extent the torque capacity utilization of the gearbox.

Radial load due to torque can be quite easily calculated if you have the appropriate information.

Inch System:

Metric System:

After calculating the radial load, the value should be compared to catalog data. Please note that different manufacturers calculate radial capacities at different speeds and different shaft locations. Typically, capacities increase at lower speeds and reduce at higher speeds. It is important to compare relevant data. It is also wise to provide safety for load due to belt tension. Excessive tension can actually create a higher radial force than that created by torque. If the calculated load is less than the rated data, you are probably good. If it's higher, there are design options to be considered.

The simplest option to consider is increasing the drive radius. Choosing a larger pulley, sprocket, or gear will have a direct relationship on the reduction of overhung load. The minimum radius allowable can be calculated using the following formula:

Other options to consider include installing a different bearing type to increase radial capacity and the possible altering of gearbox and pulley ratios to develop the optimum load to speed characteristic. All of these options can be discussed with your DieQua Representative.

Radial load capacities for all DieQua products can be found within the respective product catalog. Or, contact your Sales Support Representative for application assistance.

Remember to take a close look at the radial load issue when designing your next drive system or analyzing a reducer failure. It is a critical element too often overlooked.