1. Tire Impressions

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

3. 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.

4. 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

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

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

7. 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.

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

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

10. Recovery of Tire Evidence:
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

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

12. Analysis of Tire Evidence:
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.
Class Characteristics:
Size
Tread design
Some wear marks

13. 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.

14. Analysis of Tire Evidence:
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.