Tire Behavior

Vehicle Dynamics Govern the Motion of an Automobile

Background: Ignoring vehicle aerodynamics and collision forces, all of the external forces applied to a vehicle (bicycle, motorcycle, passenger car, race car, truck, etc,) are generated by the tires. Tire behavior is determined experimentally through flat-track tire test machines which measure forces and moments as the rolling tire is steered, braked and cambered, and also via full scale road testing.

What We Did: A Ferrari passenger car equipped with significant negative camber (tire lean angle ) was driven to the point that the inner edges of the drive wheels were worn down to the tire cord (see photo). Specially prepared tires were used that were ground to the edge-to-edge profile of the accident tires. The potential for degradation of the frictional properties of the tire in this condition was investigated using a tire test machine. We were able to show that the worn tires did not contribute to the accident loss of control.

Relevant Publications:

  • Metz, L. D. & Ruhl, R. L., “Skidmark Signatures of ABS-Equipped Passenger Cars,” SAE Paper No. 900106, [also selected for SAE SP-814](1990).
  • Metz, L. D., Akouris, C. K., Agney, C. S. & Clark, M. C., “Moments of Inertia of Mounted and Unmounted Passenger Car and Motorcycle Tires,” SAE Paper No. 900760 [also selected for Trans. SAE, J. Passenger Cars, 99:6, pp 1079-1085](1990).
  • Metz, L. D., et al., “Evasive Maneuvering Capability Without and In the Presence of a Flat Tire,” SAE Paper No. 942469 [also in SAE P-287](1994).
  • Metz, L. D., “Force and Moment Characteristics of a Typical Space-Saver Spare Tire, SAE Paper No. 2006-01-1559 (2006). 
  • Metz, L. D., “Force and Moment Characteristics of a Low-Aspect-Ratio Asymmetrically Worn Passenger Car Tire,” SAE Paper No. 2010-01-0766 [also in SAE SP-2261] (2010).
  • Metz, L.D., “Friction on Polished vs. Newly Re-rocked Oil-and-Chip Roadway Surfaces,” SAE Paper No. 2016-01-1568 [also in SAE, Int. J. Passenger. Cars, Mech. Syst., 9:2] (2016).
  • Metz, L. D., “Mathematical Analysis of Tire Delamination Failures,” SAE Paper No. 2017-01-1509 (2017).
  • Metz, L. D., “Passenger Car Handling Characteristics Associated with Space-Saver Spare Tires,” SAE Paper No. 2018-01-5027 (2018).

Ferrari tire after accident.

Tread of the vehicle's tire.

Determined vehicle tire slip during accident.

None but the liar will recoil from the probe of truth.

Sir Arthur Conan Doyle, author