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