Overview
ISO 22135:2023 specifies a calculation method to determine the steady-state rollover threshold for heavy commercial vehicles and buses. The standard provides an analytical model - not a dynamic test - to estimate the maximum lateral acceleration a vehicle can sustain in a steady turn before rolling over. The method intentionally excludes effects from active control systems and focuses on key physical contributors such as centre of gravity height, effective track, tyre lateral stiffness and vehicle roll stiffness.
Key topics and technical requirements
- Primary factors considered
- Height of centre of gravity (Hcg), sprung mass CG, and roll centre heights
- Track, equivalent track (for dual wheels) and vehicle effective track
- Tyre lateral stiffness (Cyt) and tyre normal stiffness (Czt)
- Axle, suspension and tyre-induced roll stiffness and their distribution
- Calculation workflow
- Compute equivalent and effective track (accounts for dual wheel spacing and axle loads)
- Compute axle roll stiffness from suspension geometry and tyre normal stiffness
- Sum tyre lateral stiffness across axles to obtain vehicle effective tyre lateral stiffness
- Calculate first lift-off and total lift-off lateral accelerations and interpolate to obtain steady-state rollover threshold
- Parameter accuracy
- The standard specifies required accuracies (examples): axle normal force ±500 N, track ±5 mm, roll centre and CG heights ±50 mm, tyre stiffness and suspension roll stiffness ±10%
- Scope limits and notes
- Linear tyre and suspension parameters assumed; non-linear effects (bump stops, backlash) are not considered
- Semitrailer effects covered via kingpin representative track and roll stiffness
- Alternative experimental methods: ISO 16333 (tilt-table or test track) and reference to ECE R111 calculation approach where tyre stiffness is treated as infinite
Applications and users
ISO 22135 is useful for:
- Vehicle manufacturers and chassis/suspension designers assessing rollover risk during design
- Vehicle dynamics engineers and simulation modelers validating handling and stability models
- Safety engineers and OEM compliance teams performing vulnerability or comparative analyses
- Regulatory bodies and type-approval labs using analytical estimates alongside test data
Practical applications include pre-test design evaluation, sensitivity studies (e.g., effect of load distribution, tyre choice), and integrating rollover thresholds into active safety system development (even though the method excludes active controls).
Related standards
- ISO 16333 - Experimental test methods for steady-state rollover threshold (tilt-table / test track)
- ISO 8855 - Vehicle dynamics vocabulary (normative reference)
- ECE R111 - Related calculation approaches referenced in ISO 22135 for limiting cases
Keywords: ISO 22135, steady-state rollover threshold, heavy commercial vehicles, buses, calculation method, vehicle roll stiffness, tyre lateral stiffness, centre of gravity, effective track, semitrailer, kingpin.