# Stopping Distance Calculator - Crash g-Force, Cornering, 0-100 & Energy Use

> Car physics: stopping distance by speed, reaction time and road with animation, crash g-forces, cornering and rollover limits, 0–100 time and energy use.

- URL: https://qilingtools.com/en/physics/vehicle-dynamics
- Category: Physics Tools (https://qilingtools.com/en/physics)
- Tags: [Physics](https://qilingtools.com/en/tags/physics)
- Last updated: 2026-10-29
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

A set of teaching calculators for car physics. The stopping-distance page splits reaction distance from braking distance and lets several cars at different speeds react to the same hazard, animating how fast the faster cars are still going where the slowest one stops. Three more pages estimate occupant deceleration in a crash, sliding and rollover limits on curves, and 0–100 km/h time, top speed and energy use per 100 km integrated from power, drag and rolling resistance. The models are deliberately simple, built for intuition and orders of magnitude, not accident reconstruction.

## How to use

1. Pick a tab: stopping distance, crash impact, cornering limits or acceleration & energy
2. Set speed, driver state, road surface, slope and the other inputs, or choose a preset
3. On the stopping tab, enter a few speeds to compare and press Play to watch the impact speeds
4. Read the result cards and charts, and check every formula in the box at the bottom

## Features

- Reaction plus braking distance with slope, ABS versus locked wheels
- Side-by-side animation of several speeds with the impact speed at the slowest car's stopping point
- Crash energy, average and peak g, force on the occupant, belt and airbag comparison
- Flat and banked curve sliding limits, SSF rollover threshold and a rear-view force diagram
- RK4 0–60 and 0–100 km/h runs that separate traction, torque and power limits
- Constant-speed EV kWh and petrol litres per 100 km, plotted against speed

## FAQ

### Why does going 60 instead of 50 km/h make such a difference in a crash?

Stopping distance is the reaction distance v·t_r plus the braking distance v²/2a. A 20% higher speed means 44% more braking distance on top of the extra ground covered while reacting. At the point where the 50 km/h car just stops, the 60 km/h car has barely started to slow down: on dry asphalt with a 1.2 s reaction it is still doing over 40 km/h, like falling from about 7 m.

### Why does ABS shorten stopping distance, and does it on gravel and snow?

Tyres grip best with a small amount of slip (peak friction); a locked, sliding wheel drops to the lower sliding friction, typically 10–25% less. ABS holds the wheels near the peak, so the car stops sooner and can still steer. On loose gravel or deep snow, locked wheels can build a wedge of material in front and sometimes stop shorter; the gravel values here are only typical averages.

### How is the crash g-force estimated?

With constant deceleration: average a = v²/(2d), where d is the occupant's stopping distance relative to the ground. A belted occupant rides down the car's crumple zone with the cabin, plus belt stretch and airbag compression. An unbelted occupant keeps moving after the car stops and hits the interior with only a few centimetres of give, so the g-force is about ten times higher. Real crash pulses peak at roughly 1.5–2 times the average.

### When does a vehicle roll over before it slides?

When the static stability factor SSF = track width / (2 × centre-of-gravity height) is lower than the tyre friction coefficient, the tipping condition is reached first. Cars have an SSF of about 1.3–1.5 against about 0.9 grip on dry roads, so they usually slide. Tall vans and double-decker buses are near or below 1 and can tip first. Suspension roll and tripping on kerbs make real rollovers happen even earlier.

### Why does energy use climb so fast at motorway speeds?

Aerodynamic drag ½ρC_dAv² grows with the square of speed, and the energy per 100 km is simply the resisting force times 100 km. For a compact car about 70% of the road load at 100 km/h is drag, and 120 km/h costs roughly 50% more energy than 90 km/h. An EV's drivetrain is far more efficient, so for the same road load it uses about a third of the energy of a petrol car.

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