Tires

  • Tire impression: 2 or 3-D marks that reflect the trend design and dimensional features of tires
  • Tire track: the relative dimensions between two or more tires of a vehicle
  • This kind of evidence can help prove a suspect’s vehicle was present at the crime scene, reconstruct events, and lead to other evidence.
  • Background info
    • Tires come in all shapes and sizes
    • Tires on new vehicles are known as original equipment (OE) tires
    • Same make and model vehicles will have the same tire size and brand
    • Tires purchased to replace worn down or damaged tires are called replacement tires
    • Replacement tires are usually not the same design as OE
    • Tire construction
    • Made of various compounds of rubber, steel, and fabric
    • Tire is constructed without any design first (green tirie) before beijing placed in a mold where tread and sidewall designs are added
  • Tire tread and sidewall components
    • Tread design components can be associated with a brand name and manufacturer
    • Sidewall components
    • Label side (face outward)
    • Serial side (face inward)
    • Important forensic info
    • Tire brand and style name (both sides)
    • Tire size (both sides)
    • Department of transportation (DOT) # (serial side)
      • DOT-symbols for manufacturer-week and tire year made
    • Some tires are retread ➝ have DOTR number
  • Noise Treatment
    • As tires rotate, the design elements vibrate and produce noise
    • If all elements were the same size, the noise would be very loud (pitch)
    • Noise treatment = tire industry creating tire designs that vary the size of the design elements around the tire
  • Tread wear indicators
    • Wear bars indicate when tire should be replaced
    • Can be retained in 3d impressions
  • Tire track evidence
    • Includes tire track width, wheelbase dimensions, and turning diameter
    • Tire track width = measurement made from center of one wheel to center of the opposite
    • Wheelbase dimensions = measurement between the centers of the hubs on the front wheels to the center of the hubs of the rear wheels
    • Turning diameter = diameter of the circle a vehicle makes when steering wheel is fully turned
  • Recovery of Tire Evidence
    • general crime scene photographs and notes
    • Examination quality photograph
    • Casting
    • Any impression 4 ft or smaller should always be cast
    • Cast offers best physical evidence for later comparison with a tire
  • Tire evidence examination
    • Treads will be compared with known tires (suspect vehicles, elimination vehicles)
    • If similar design, the tires must be analyzed further to make a match
    • Will need to make a test impression with suspect tires
    • Analysis includes:
      • Closer look at tread design elements, grooves, and sipes
      • Tread dimension and track characteristics
      • Noise treatment and wear features
      • Random individual characteristics or distinguishable marks
      • Multiple tires of different designs