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Forensic Tire Impression and Tire Track Evidence. Tire Impressions reflect the tread design and dimensional features of individual tires on a vehicle Tire Tracks are relational dimensions between two or more tires: tracks can be used to determine the wheelbase of the vehicle.
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Forensic Tire Impression and Tire Track Evidence • Tire Impressions reflect the tread design and dimensional features of individual tires on a vehicle • Tire Tracks are relational dimensions between two or more tires: tracks can be used to determine the wheelbase of the vehicle
Tread Nomenclature and Sidewall Information • Department of Transportation number, known as DOT number – consists of:
Tread Nomenclature and Sidewall Information • Retread tires – have slightly different numbers • DOTR YPY 1201 • DOTR – Department of Transportation retread • YPY – Manufacturer retread • 1201 – date and year of manufacture
Tire Track Evidence • Tire track evidence consists of: • Tire track width • Wheelbase dimensions • Turning diameter • Relative positions of turning tracks
RECOVERY • Tire impressions must be: • Photographed from all angles with and without measurement tool (ruler) • Cast – a 3 foot impression requires 15-25 pounds of dental stone • Measured – width, length and depth • Direction of travel noted • Impressions made if possible, and • Pictures of the source (tire) must be included for comparison
COMPARISONS • Tire tread examinations compare the tire impressions recovered from scene with tires taken from a known vehicle • Two categories of tires: • Suspect - Vehicle of suspect • Elimination - Vehicles of police, ambulance, etc • All tires should be seized from suspect vehicle for comparison
COMPARISONS • Forensic examination begins with visual comparison and elimination of tires which do not match impression • Forensic examination continues with full circumference test impressions • Impressions are superimposed on known impression over cast or original tire