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

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