Definition: Shock load rating describes a caster’s ability to withstand sudden, short-duration load spikes above its normal operating load.
What it affects: Structural integrity, bearing life, and resistance to catastrophic failure.
Why shock load rating matters
Casters frequently experience loads far higher than their rated capacity during impacts and transitions.
- Occurs when rolling over thresholds, dock plates, and debris
- Common during drops, curb impacts, and floor transitions
- Amplified in rigid frames and high-speed movement
- Causes sudden stress on wheels, bearings, and forks
Reality: Shock loads are the leading cause of cracked wheels, bent forks, and bearing failure.
Common sources of shock loading
- Floor joints and expansion gaps
- Dock plates and ramps
- Uneven or damaged concrete
- Manual drops or impacts during handling
Design factors that affect shock resistance
| Design factor | Impact on shock resistance |
|---|---|
| Wheel material | Softer materials absorb shock better |
| Wheel diameter | Larger diameters reduce impact severity |
| Kingpin vs kingpinless | Kingpinless designs handle shock better |
| Fork thickness | Thicker forks resist deformation |
Common engineering mistakes
- Using static or dynamic load ratings as shock ratings
- Selecting very hard wheels in impact-prone environments
- Ignoring speed and operator behavior
- Underestimating floor condition variability
Rule: If impacts are unavoidable, derate capacity or upgrade caster design.
FAQs
Are shock load ratings published?
Rarely. Shock resistance is typically inferred from design and application experience.
Can softer wheels eliminate shock damage?
No, but they significantly reduce peak impact forces.
Does speed affect shock loading?
Yes. Higher speed dramatically increases impact forces.
How do I design for shock loads?
Use larger wheels, softer materials, kingpinless designs, and appropriate safety factors.