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Wheel Chock Sizing: A Practical Guide for Fleet Operators
An undersized wheel chock does not fail loudly. It creeps, then it slips, then the vehicle moves. Sizing a chock correctly is a two-minute calculation that prevents a category of accident most fleets never see coming.
The core rule: chock height vs. wheel diameter
A wheel chock works by presenting a wedge taller than the tyre can climb without deforming. The industry rule of thumb:
Chock height ≥ wheel radius ÷ 4, or roughly one-quarter of the tyre diameter. Below that, the tyre rolls over the chock instead of being stopped by it.
| Vehicle | Tyre diameter | Min. chock height | Typical model |
|---|---|---|---|
| Car / small van | 600–700mm | 100mm | Small rubber chock |
| Box truck / rigid | 800–900mm | 130mm | Medium rubber chock |
| Semi-trailer / bus | 1000–1100mm | 150mm+ | Heavy-duty chock |
| Mining / earthmoving | 1800mm+ | 250mm+ | Oversized custom chock |
Load matters as much as height
A chock that is tall enough but too light will split or extrude under a loaded truck. Check the maximum axle load the chock is rated for. Standard rubber chocks are rated 3–10 t; heavy-duty polyurethane or steel-reinforced models go to 40 t and beyond.
Multiply your gross vehicle weight by the number of axles you are chocking, then add a safety factor of at least 1.5. A 32-tonne semi chocked on two axles is not a 16-tonne problem.
Slope changes the calculation
On a flat surface, chocking the downhill side is enough. On any slope — and “flat” asphalt in a yard is rarely flat — you need more:
- Up to 3% grade: chock both rear wheels on the downhill side
- 3–8% grade: chock both sides of at least one axle, plus set the parking brake
- Above 8%: chock both sides of two axles, and do not rely on the parking brake alone
Material: rubber, polyurethane, or steel
Rubber grips best on wet or oily concrete and will not spark — the right default for warehouses, depots, and fuel-handling areas.
Polyurethane is lighter, resists oil and chemicals better, and lasts longer outdoors. Costs more per unit.
Steel is used for mining and heavy plant where loads exceed what polymer chocks handle. It is heavy and can spark, so it is not a general-purpose option.
Watch for oil. A rubber chock on an oil-soaked floor has a fraction of its dry grip. If your yard has hydraulic leaks, switch to polyurethane or specify an oil-resistant compound.
Three things fleets get wrong
- Chocking only one wheel per axle. The unchocked wheel on the same axle lets the vehicle pivot. Chock both sides.
- Using the parking brake as the primary restraint. Brakes fail, cables stretch, and air systems bleed down. The chock is the primary restraint; the brake is backup.
- Leaving chocks on the ground when vehicles depart. Run-over chocks are the single most common cause of chock replacement. Get a wall-mounted rack and make stowing part of the departure checklist.
Equip Your Fleet Correctly
Tell us your vehicle types, axle loads, and floor conditions. We will spec the right chock sizes and quantities, with oil-resistant or anti-spark compounds if you need them.
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