Vehicle Rollover Stability Factor Calculator
Vehicle dynamics & crash avoidance: Calculate the NHTSA Static Stability Factor (SSF = T / 2H), critical lateral tip-over acceleration, and un-tripped rollover risk.
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Frequently Asked Questions
What is the Static Stability Factor (SSF) and why did NHTSA mandate it?
The Static Stability Factor SSF = T / (2 * H_cg) is a fundamental geometric ratio that compares a vehicle's half-track width (T/2) to its center-of-gravity height (H_cg). In rigid-body physics, when lateral cornering acceleration a_y exceeds SSF * g, the overturning moment exceeds the righting moment, lifting the inside tires off the road. Mandating SSF public ratings spurred automakers to widen track widths and lower powertrains to earn 5 stars.
What is the difference between tripped and un-tripped rollovers?
An un-tripped rollover occurs purely from severe lateral tire friction on dry pavement during high-speed steering maneuvers (fish-hook tests) when tire grip exceeds the vehicle's rollover threshold. A tripped rollover (which accounts for ~95% of real-world rollovers) happens when a skidding vehicle slides sideways into soft ditch soil, curbs, or guardrails, violently tripping the tires into an airborne roll.
How does roof cargo dramatically increase rollover risk?
Because the roof sits high above the ground (typically 1.5 to 1.9 meters), placing just 75 to 100 kg of cargo (roof boxes, kayaks, luggage) on roof racks shifts the vehicle's overall center of gravity upward by 30 to 50 mm. This lowers the SSF significantly, turning a 4-star stable vehicle into a rollover hazard.