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SRT Calculator

This tool estimates the Static Rollover Threshold (SRT) of a heavy vehicle or trailer unit based on its dimensions, axle group configuration, suspension, tyre properties, and payload characteristics.

SRT is a measure of rollover stability during steady and level cornering and is required for certification in certain networks. A minimum SRT of 0.35g or 0.40g typically applies, depending on whether dangerous goods are carried.

Start by selecting a vehicle configuration, then enter the required details in each section. You can use the “Target SRT” setting to compare against required thresholds.

For trailers, ensure you provide accurate payload height and suspension data. Warnings will appear for values outside typical safe ranges.

This calculator is based on the TERNZ Static Rollover Threshold Calculator v3.01wa, developed by the Transport Engineering Research New Zealand (TERNZ) group. Validation of the original calculators method using a tilt table has been undertaken as outlined in the report (2001).

For more information on usage, refer to the SRT Calculator User Guide.

SRT image
This value sets the minimum rollover threshold required.

Select the type of vehicle or unit being configured.
Number of axles at the front of the unit (usually truck or lead trailer).
Number of axles at the rear of the unit (drive or trailer group).

Front Tyres
m
Width between outer edges of the outer tyres. Used to calculate track width.
Rear Tyres
m
Width between outer edges of the outer tyres. Used to calculate track width.

Front Axle Group
kg
The maximum front axle group mass at which the vehicle will operate.
kg
The unladen vehicle front axle group mass.
kg
Rear Axle Group
kg
The maximum rear axle group load at which the vehicle will operate.
kg
The unladen vehicle rear axle group mass.
kg
Front Unsprung Mass (Optional)
kg
Overrides the mass of the front unsprung components (e.g. axle, wheels).
kg
m
Overrides the centre of gravity height of front unsprung mass.
Rear Unsprung Mass (Optional)
kg
Overrides the mass of the rear unsprung components (e.g. axle, wheels).
kg
m
Overrides the centre of gravity height of rear unsprung mass.
Sprung Tare Mass Details (Optional)
m
Overrides the vertical distance from ground to the centre of gravity of the sprung mass.
kg
Tare masses less unsprung masses.

Geometry of the vehicle deck influencing load-height calculations.
m
Height of the deck floor above ground in laden condition.
m
Peak height of the payload or body.
Estimate payload CG height based on load type or specify (only standard deck style).
m
Specified vertical distance from ground to the centre of gravity of the payload.

Front Suspension
Rear Suspension

SRT Result

Static Rollover Threshold
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Pending
Tilt Angle (φ)
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No speed results available. Please calculate SRT first.