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 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