Forensics Tire impressions

Where are tire impressions usually found

○ In road accident scenes

○ In the access and escape routes of other crime scenes.

Class evidence

Tracks help investigators identify the TYPE of vehicle that left them

Collection of evidence

○ Investigators may make ink prints of a tire or plaster casts of a track.

○ They will also take photographs

that can later be used to prove a match

Collection Methods

Investigators analyze impressions for unique characteristics to link shoes, tires, tools, and other objects found in suspect's possession to evidence at a crime scene.

Collection of impression evidence must follow this exact procedure:

1)Photograph and measure all impression evidence

2)Carefully cast with Plaster of Paris

What to look for class evidence

Tread pattern/width/depth

Brand and model of the tire that left impression

Type of vehicle (make of model)

What to look for individual evidence

Any unique characteristics due to the wear patterns or any defects.

Tread Pattern

the unique design of a tire's surface that channel water away and provide traction

Tire Treads and Impressions

•Tread patterns can indicate the type of vehicle that left the mark

•Link a suspect or victim to a crime scene

•Reveal events that took place at the scene

Patent tread patterns

impressions made after tire runs through a fluid material

Latent tread patterns

impressions from tire oils used to keep tires soft and pliable

Plastic tread patterns

three dimensional impressions left in soft surfaces

recording tread impressions

Count ridges and grooves across the tire width

Note unique characteristics—wear or pebbles embedded in the grooves

Create a print of the suspect's tire impressions through one revolution

Compare impressions from the crime scene and suspect's tire

Identifying tread patterns may not be enough to link a suspect with a crime scene

Tread Area

The part of a tire that meets the road

Tire Groove

a depression in the tread pattern

tire rib

an individual ridge of tread running down the tread area and around the circumference of the tire

Tire Ridge

elevated area on the tread pattern (everything that is not a groove)

Wheel Base

The distance from the center of the front axle on a vehicle to the center of the rear axle.

Turning Diameter

a measure of how tight a circle can be driven by a vehicle or U-turn

track width

the distance from the center of the tread pattern on the left tire to the center of the tread pattern on the corresponding right tire

Accident Reconstruction *This is mostly done in a fatal car accident*

•Drivers may not recall the exact series of events before, during, and after an accident

•People, vehicles, and objects, however, can leave evidence of their actions at the scene of an accident

•Debris patterns and tire marks can be clues to speed, direction, and vehicle identification

Skid marks

clues to the distance traveled after brakes are applied and the vehicle's speed. Formed when someone brakes suddenly and lock the wheels

Yaw marks

Shows a sideways skid

Formed when a vehicle travels in a curved path faster than the vehicle can handle and skids

Tire scrub

Determines the area of impact formed by a damaged or overloaded tire or tires during or immediately after impact.

What type of evidence are Tire Impressions?

•Circumstantial/Indirect

•Physical

•Class

-can be individual with unique characteristics

What type of impressions are tire impressions?

Can be ALL 3 (latent, patent, plastic)