7/27/2019 Tire+Impression+Evidence

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TIRE IMPRESSION EVIDENCE

TYPES OF TIRE CONSTRUCTION1. Bias Construction: Bias (angle) construction may be two, four or more plies placed on top of one

another in alternating directions on the bias. The tire body ply cords run from bead to bead.

2. Belted-Bias Construction: In belted-bias construction, the cord body is constructed as in bias

construction, with the cord in the body plies running at an angle from bead to bead. However, two or morebelts are then applied on top of the body plies directly under the tread area only. Regardless of the type of

cord material used, adding these high-strength, low-elongation belts lessens the stress on the cord body

greatly and stabilizes the tread area of tire.

3.Radial-Ply Construction: Radial construction utilizes one or more body plies, with the cords running in

a straight line from bead to bead. On the top of these body plies are two more belt plies, referred to as

stabilizer belts. These stabilizer belts prevent twist in tread area and give tire a lateral stability.

BASIC COMPONENTS OF ALL TIRES1. Beads: As tire rotates, the internal air pressure and centrifugal force tries to throw the tire off the rim.

To prevent this, the plies of the tire are wrapped around a bronze plated, high tensile steel wire, called

beads. The beads anchor the tire to the rim, and are held in their proper place on the rim by air pressure

within the tire.

2. Cord Body: Layers of rubber coated cord, called plies, laid on top if one another and bonded together;

make up the cord body of the tire. The cord body provides strength to the tire and acts as a container for the

air pressure within the tire.

3. Tread: The portion of tire in contact with the road surface is tread.

4. Sidewall: The area from bead to tread is the sidewall. It forms a protective covering for the cord body.

Side wall rubber is blended to resist cracking, cutting and snagging.

5. Belts: Strong layers of cord under the tread area of the tire are known as stabilizer belts.

TYPES OF TIRE PRINTS1. Plastic Prints: Plastic tire impressions are impressions that occur when the tire tread rolls over a soft

pliable surface, such as deep mud or snow, wet sand, tar, or even the body of victim. This produces a

negative impression of tread element, resulting in a plastic print.

2. Positive Visible Impression: Positive visible tire prints occur when the tire tread rolls over a foreignsubstance and is contaminated by it, and then comes in contact with a clean surface and is pressed onto

that surface.

3. Negative Visible Impressions: Negative visible impressions occur when a tire tread rolls over a thinfilm of dust, water, oil, snow or the like, and actually lifts that substance, laying negative impression on

clean road surface.