Static roll threshold calculator

Welcome to the SRT calculator

This calculator program can be used to assess the stability of most standard heavy vehicles (not buses).

Note: The SRT calculator has been updated (September 2003) to include the following additional features:

• sloping deck vehicles
• vehicles with two level decks at different heights
• a table in the results page to show acceptable intermediate gross mass /load height combinations for vehicles which do not meet SRT at full mass and full height
• updated Help page and User Guide.

The following features are also included in the Calculator:

• Provision for trucks with two front axles and one rear axle;
• Two types of Generic Air Suspension (High Stiffness and Low Stiffness);
• Provision for overweight vehicles up to a Vehicle Axle Index of 1.1.;
• Provision for very stiff suspensions;
• Conversion factors to convert from different systems of units;
• A printable Calculation Summary page.

It is designed for use with class TD trailers (with a Gross Vehicle Mass over 10 tonnes) and class NC trucks (with a Gross Vehicle Mass over 12 tonnes). Both these classes of vehicle will need to have a minimum Static Roll Threshold (SRT) of 0.35 g to comply with the Vehicle Dimensions and Mass Rule. Only Class TD trailers with a body or load height above 2.8 metres need to be certified for SRT.

See the updated Factsheet 13e "Static Roll Thresholds" for the conditions and implementation dates for these requirements. Details of the appropriate type of certification for a particular vehicle (level 1 or level 2) are included.

See Heavy vehicle stability guide (PDF, 170 KB) for information on heavy vehicle stability issues and suggested techniques for minimising the risks of rollover and loss of control crashes.

If you have any suggestions for improvements to SRT Calculator, please email them to info@nzta.govt.nz.

Last updated: 4 September 2003
Page created: 11 June 2002