Tire Impressions

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Tire Impressions

• Jason Linville
• University of Alabama at Birmingham
• jglinvil_at_uab.edu

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Tire Impression Evidence

• What is tire impression evidence?
• How is it involved in crime scenes?
• How is it collected?
• How is it analyzed?

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Tire Impressions

• 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.

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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

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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
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Tire Impressions

• Noise Treatment

• If tire design was exactly repeated around the
  tire, noise would result.

• Design repeated at different pitch lengths

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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.
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Tire Impressions

• Tire Track Evidence

Wheelbase measured from front center to back
center
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Tire Impressions

• Tire Track Evidence

Turning Diameter Diameter of a circle made when
the wheels are fully turned.
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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

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Tire Impressions

• Recovery of Tire Evidence

• Cast can be made of 3-D impressions

• Long sections (3 feet) should be cast.
• Use dental stone

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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

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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.
Known tires collected. Inked or 3D impressions
can be made for comparison.
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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.