Tire Impressions

Tire Impression Evidence  What is tire impression evidence?  How is it involved in crime scenes?  How is it collected?  How is it analyzed?

What are tire impressions or tracks?  Tire Impressions are the tread design and dimensions of a tire.  Tire Tracks are the related dimensions of the 4+ wheels. Tire Impressions

Different Types of Tires: Original Equipment (OE) Tires  sold on new cars  thousands of cars have same brand and size Replacement Tires:  purchased to replace old, worn tires  usually different than OE tires Tire Impressions

Design Elements: Grooves: around a tire Sipe: small grooves Slots: across a tire Tread Wear Indicator: raised bar under design; shows after wear Tire Impressions

Noise Treatment:  If tire design was exactly repeated around the tire, noise would result.  Design repeated at different pitch lengths Tire Impressions

Tire Track Evidence: Track width: measured from right center to left center Track width of front tires and rear tires are not always the same. Tire Impressions

Tire Track Evidence: Wheelbase: measured from front center to back center Tire Impressions

Tire Track Evidence: Turning Diameter: Diameter of a circle made when the wheels are fully turned. Tire Impressions

Recovery of Tire Evidence:  Photos taken along with log of location.  Since tire tracks are variable along length (pitch), entire track should be photographed (examination quality) with overlapping photos.  Ruler included Tire Impressions

Recovery of Tire Evidence:  Cast can be made of 3-D impressions  Long sections (3 feet) should be cast.  Use dental stone Tire Impressions

Analysis of Tire Evidence: Class Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track.  Size  Tread design Tire Impressions  Some wear marks Class Characteristics:

Analysis of Tire Evidence: Class Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track. Known tires collected. Inked or 3D impressions can be made for comparison. Tire Impressions

Analysis of Tire Evidence:  Similar to shoes, individual characteristics can be used to identify an exact tire.  Remember, individual characteristics change over time. Tire Impressions