CHAPTER 16 — Tread (Shoe & Tire) Impressions

1. What Are Tread Impressions?

Patterns left by:

  • Shoes

  • Tires

They can show:

  • Direction of movement

  • Brand/type

  • Wear patterns

2. Types of Impressions

2D Impressions

  • Dust, blood

  • Photographed or lifted

3D Impressions

  • Mud, snow

  • Cast with dental stone

3. Class vs. Individual Characteristics

Class

  • Shoe size

  • Tread pattern

  • Manufacturer design

Individual

  • Wear

  • Cuts

  • Nicks

  • Random damage

4. Collection Methods

  • Photography (with scale)

  • Lifting (gel or electrostatic)

  • Casting (3D impressions)

CHAPTER 16 TAKEAWAYS

  • Impressions are pattern evidence

  • Wear increases individuality

  • Proper collection is critical


Accidental marks

  • Random marks caused by wear, damage, or use

  • Not part of the original design

Examples:

  • Cuts

  • Scratches

  • Chips

  • Embedded stones

📌 Why they matter:
These marks make impressions more unique and help link a shoe or tire to a specific source.

Dental stone

  • A special type of plaster-like material

  • Used to make casts of impressions

Used for:

  • Shoe prints

  • Tire tracks

  • Footprints in mud, snow, or soil

📌 Why it matters:
It hardens quickly and captures fine details without damaging the impression.

Dry origin impression

  • An impression made without moisture

  • Caused by dry dirt, dust, or residue

Examples:

  • Dusty shoe print on a tile floor

  • Powdery footprint on concrete

📌 These are usually:

  • Two-dimensional

  • Collected by photography or lifting

Stance

  • The distance between the left and right feet

  • Measured from the center of one foot to the other

📌 Why it matters:
Stance can give clues about:

  • Height

  • Body build

  • How someone walks or stands

Three-dimensional impressions

  • Impressions that have depth

  • Made in soft surfaces

Examples:

  • Mud

  • Snow

  • Sand

  • Wet soil

📌 These are best collected by casting with dental stone.

Tire tracks

  • Impressions left by a moving vehicle’s tires

  • Can show:

    • Direction of travel

    • Speed

    • Type of vehicle

📌 Can include:

  • Tread patterns

  • Wear marks

  • Accidental damage

Turning diameter

  • The smallest circle a vehicle can turn within

  • Shows how sharply a vehicle can turn

📌 Why it matters:
Helps investigators understand:

  • Vehicle movement

  • Maneuvers at a crime scene

Wheelbase

  • The distance between the front and rear wheels of a vehicle

📌 Why it matters:

  • Helps narrow down vehicle type

  • Used to compare tire track patterns

🧠 QUICK MEMORY TRICKS

  • Accidental marks = random damage

  • Dental stone = casting material

  • Dry origin = no moisture

  • Stance = foot spacing

  • 3D impressions = depth

  • Tire tracks = moving vehicle

  • Turning diameter = how tight a turn

  • Wheelbase = front-to-back wheel distance