Skid Mark
Definition
A dark rubber deposit left when locked wheels slide along the road surface. Length combined with the friction coefficient allows calculation of minimum entry speed using the standard kinematics equation.
- Appearance
- Dark rubber deposit on the road surface
- Cause
- A locked wheel sliding rather than rolling
- Primary use
- Estimating minimum pre-braking speed
- Key inputs
- Mark length and the road-tyre friction coefficient
Common questions
Why is the calculated speed described as a minimum?+
The formula only accounts for speed lost during the visible sliding phase, so any braking before the tyre locked or speed changes after the skid ended are not captured, understating the true speed.
Do vehicles with ABS leave conventional skid marks?+
Rarely, because ABS prevents full wheel lockup, so reconstructionists often rely on other evidence like yaw marks or event data recorder output instead of a classic skid mark.
Related terms
- Coefficient of Friction (Mu)
- The dimensionless ratio of frictional force to normal force between tire and road. It determines how quickly a skidding vehicle decelerates. Typical...
- Conservation of Momentum
- In a collision, the vector sum of all momenta (mass × velocity) before impact equals the vector sum after, provided no significant...
- Critical Speed Yaw Mark
- Curved scuff marks deposited when a vehicle slides sideways. The radius of curvature and friction coefficient yield the vehicle's minimum speed at...
- Delta-V
- The change in vehicle velocity during the crash event, recorded by the EDR as a time-history. It is the integral of the...
- Perception-Reaction Time (PRT)
- The elapsed time from when a driver can first perceive a hazard to when the brakes begin to apply. Olson and Farber...