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Vehicle Stability Factor Calculator

2026-09-27 6 min

Static stability factor (SSF) and rollover-G threshold from track width and CG height.

Stability Factor
1.50 SSF
Rollover Threshold
1.50 g

Calculator

Track Width(in)
in
CG Height(in)
in
Results update live as you type

Live statistics

Stability Factor

1.50 SSF

Rollover Threshold

1.50 g

Results

Optimal

Stability Factor

1.50SSF

Rollover Threshold

1.50g

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

1.5Stability Factor
1.5Rollover Threshold

Stability Factor vs. Track Width

Stability Factor

1.5SSF
0.81.8

Formula

NHTSA static metric: footprint half-width over CG height approximates tip-up lateral acceleration.

SSF = track / (2 x CG height)

Alternative Form

Rollover threshold ~ SSF in G

Variables

SymbolNameUnitDescription
SSFStatic stability factor-Higher = more stable

Explanation

Tall narrow vehicles tip near 1.0 g while sports cars exceed 1.5 — geometry decides the ceiling before suspension helps.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Track Width:60 in
CG Height:20 in
Result: 2 inputs ready
Step 2

Apply the formula.

SSF = track / (2 x CG height)
Result: Primary result = 1.50 SSF
Step 3

Read every derived output.

Stability Factor:1.50 SSF
Rollover Threshold:1.50 g
Result: Stability Factor = 1.50 SSF
Final Answer
1.50

Worked Examples

See how the calculator works with different scenarios.

Scenario

Sport sedan.

Inputs

Track:60 in
CG:20 in

Calculation

60/40 = 1.50

Result

SSF 1.50, ~1.50-g threshold.

Interpretation

Five-star rollover territory; tires saturate before tip-up.

Understanding Your Result

Your Result: Stability Factor: 1.50 SSF

What This Means

Geometric rollover resistance in one number.

Why It Matters

Screens lift, load and tire upgrades for tip-up risk.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

  • •Double-check units on every input before trusting the result
  • •Compare against the worked example below to sanity-check magnitude
  • •Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Tip-up risk is footprint width versus CG height.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

  1. Fill to first click at the same pump, record the odometer (Tank 0).
  2. Drive normally for 2–3 tanks; always refill to first click at the same pump.
  3. MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
  4. Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
  5. Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

  • •Roof loads raise CG fast — recheck SSF
  • •Wider track wheels help modestly
  • •Tires that grip past SSF need care

Common Mistakes

Mixing units (inches with mm, psi with kPa)
Convert every input to the unit shown on its field before calculating.
Trusting a single output blindly
Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.
Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.
No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

What SSF is safe?
NHTSA 5-star needs ~1.24+; sports cars run 1.4-1.6; tall SUVs dip near 1.0-1.15.
Does suspension change SSF?
No — SSF is pure geometry. Suspension changes dynamic rollover, not the static factor.

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG
Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km
Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe
Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE
Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance
Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag
Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling
Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II
On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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