The size of a monorail guidance system is determined by the demands made on its load carrying capacity, rating life and operational security.

The load carrying capacity is described in terms of the basic dynamic load rating C, the basic static load rating C₀ and the static moment ratings M_0x, M_0y and M_0z, Figure 1.

The calculation of the basic dynamic and static load ratings given in the dimension tables is based on DIN 636-1 and 2.

Suppliers from the Far East frequently calculate basic load ratings using a basic rating life based on a distance of only 50 km compared with 100 km to DIN .

The dynamic load carrying capacity is described in terms of the basic dynamic load rating and the basic rating life.

The basic dynamic load rating is the load in N at which the guidance system achieves a distance of 100 km at a survival probability of 90% (C₁₀₀).

The basic rating life L and L_h is achieved by 90% of a sufficiently large group of apparently identical bearings before the first evidence of material fatigue occurs.

According to DIN 636-1, the equivalent dynamic load P should not exceed the value 0,5 · C.

The formulae for calculating the basic rating life assume that the load P and speed  are constant. Non-constant operating conditions can be taken into consideration by means of equivalent operating values. These have the same effect on the life as the loads occurring in practice.

Where the load varies in steps, the equivalent dynamic load is calculated as follows:

Where the speed varies in steps, the equivalent dynamic speed is calculated as follows:

If the direction of the load acting on an element does not coincide with one of the main load directions, an approximate value for the equivalent load is calculated as follows:

If an element is simultaneously subjected to a force F and a moment M, an approximate value for the equivalent dynamic load is calculated as follows:

The operating life is defined as the life actually achieved by monorail guidance systems. It may differ significantly from the calculated life.

The following influences can lead to premature failure through wear or fatigue:

• excess load due to misalignment as a result of temperature differences and manufacturing tolerances (elasticity of the adjacent construction)
• contamination of the guidance systems
• inadequate lubrication
• reciprocating motion with very small stroke lengths (false brinelling)
• vibration while stationary (false brinelling)
• overloading of the guidance system (even for short periods)
• plastic deformation.

The static load carrying capacity of the monorail guidance system is limited by:

• the permissible load on the monorail guidance system
• the load carrying capacity of the raceway
• the permissible load on the screw connections
• the permissible load on the adjacent construction.

For design purposes, the static load safety factor S₀ required for the application must be observed, see tables starting link.

The basic static load ratings and static moment ratings are those loads under which the raceways and rolling elements undergo a permanent overall deformation corresponding to 1/10 000 of the rolling element diameter.

The static load safety factor S₀ is the security against permanent deformation at the rolling contact:

The equivalent static bearing load is determined in approximate terms from the maximum loads:

Static load safety factor S₀ for design of linear guidance systems, see tables starting link.

For the design of linear guidance systems, the static load safety factor S₀ according to the following tables must be taken into consideration.

If the fixing screw threads are of a sufficient size, monorail guidance systems can be subjected to loads up to the static load carrying capacity C₀ and M₀ according to the dimension tables.

The load must be transmitted via locating surfaces.