Lecture 19 Tire Print Evidenc e - PowerPoint PPT Presentation

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Lecture 19 Tire Print Evidenc e

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  1. Lecture 19Tire Print Evidence Evidence Often Overlooked

  2. Tread Wear

  3. Tread Wear Indicators Tread wear indicators (wear bars) Located in grooves of tread design Run laterally across tread 1/16” above base of the groove Useful for comparison purposes Divide tire into useful segments Cars & light trucks 6 evenly spaced Rim diameter of 305mm/12 inches must have @ least 6 Less than 305mm must have @ least 3/12 inches Wear Bar Indicator

  4. Tread Wear First thousand miles produces the fastest tread wear As elements become shorter Flex less & squirming is reduced Slows considerably Accidental characteristics last longer on well-worn tire than on a new one Tire wear indicator

  5. Factors Affecting Tread Wear Excessive under-inflation Excessive over-inflation Balancing Improper toe-in-out Improper camber Chunking Faulty breaks Combined suspension steering issues Bad repairs

  6. Measuring Tread Depth Non-Skid Depth • Equipment: • Tread depth gauge (Measures in 1/32nds) or 15mm ruler • Newer tires: 11/32 to 16/32” • Maximum depths suggest newer tires • Wear bars are set @ 2/32nds, • Wear patterns appear as solid bar in the tire impression • Procedure • Estimate height of groove in scene impression • Set depth gauge on impression groove • Carefully lower gauge into impression & read depth from the scale • Alternatively, measure depth from cast in dental stone

  7. Tread Depth - Some Statistics • When tires near end of life, • U.S. Lincoln penny can be used to confirm the tire's tread depth. • If Lincoln's entire head is visible, the tire is worn to approximately 2/32" and is considered legally worn out in most States. • Average new tires used on cars typically start with 10/32" to 11/32" of original tread depth. • Dedicated winter / snow tires and light truck tires typically are deeper - how much deeper depends on tire's tread type ... Highway Rib, Highway All Season, Off Road All Terrain or Off Road Maximum Traction). • Means - original tread depth has only 8/32" of useable tread depth. • Useable tread depth calculated by subtracting a worn out tire's 2/32" from the new tire's original depth of 10/32". • The final 2/32" of a tire's tread depth isn't part of the equation when it comes to calculating tread depth percentages because the tire is already legally worn out. • Remaining tread depth used to calculate tread wear percentages. … • Tire that started with 10/32" of original tread depth and has worn off 4/32" (down to 6/32" of remaining tread depth) is 50% worn. • 2/32" legally worn out tread depth • A tire that starts with 10/32" of original tread depth has 12.5% wear for every 1/32" that is worn away, and a tire that starts with 12/32" " of original tread depth, has 10% wear for every 1/32" that is worn away, http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=197

  8. Identifying Tread Wear Exposed tire bars Tire bars recessed in sipes & grooves become exposed Circular wear Wear around circumference w/sipes & grooves indicates wear 2/32 Tread Legally Worn 4/32 Tread 6/32 Tread

  9. Enhancing Tire Tracks

  10. Enhancing Tire Track Impressions • Involves many of the same principles as for footwear evidence • Photography : • A method for archiving AND enhancing. • Chemical enhancements. • Chemical treatments take advantage of the inherent chemical signature of the impression • Minerals, such as iron and aluminum, etc, organics, or bio-materials – to more clearly visualize the impression. • The chemical enhancements are essentially the same those used to enhance footwear evidence.

  11. Chemical EnhancementMetals in Soil Impressions with Metals Ammonium or Potassium Thiocyanate Tests for Iron Reddish brown 8-Hydroxyquinoline Iron, magnesium + other metals Fluorescent under UV light • Impression w/oil or fats • Iodine fuming or Iodine crystals • Oils & Other organic compounds • Iodine absorbed • Enhancement • Benzophenone • Forms stable blue color • Thin layer of starch powder • Subsequent steam treatment turns starch blue

  12. Chemical EnhancementWet Tires with Salt Deposits - Winter Silver Nitrate Converts NaCl (salt) to AgCl (Silver Chloride) NaCl + AgNO3AgCl + AgNO3 Ag Metal UV or sunlight darkens impression 2% Silver Nitrate In Methanol hv Road Salt

  13. Tire Tracks in BloodChemical Enhancement Blood reactive chemicals DAB Leucocrystal Violet Acid Violet 17 Acid Yellow 7 – dark surfaces – yellow fluorescence Amido Black Ninhydrin DFO Crowle’s Stain TMB Coomassie blue Nile Red Hungarian Red Ashley’s reagent

  14. Investigative EvidenceIdentifying Unknown Vehicle

  15. Tire Impressions as Investigational Aids Identifying manufacturer & brand name Done after processing the scene Tread design Who makes it & where Tire guides – Boca Raton, FL • Shows tread patterns for all types of tires sold in the U.S. • Comprehensive Visual Identification of all types of Tire Tread Pattern Designs. • Covers Passenger, Light Truck and Medium Truck vehicles. • Includes Off-Road and Agricultural Tread Patterns. • Also covers Motorcycle and retread tire tread designs. • Provides information on how to read a tire sidewall and on the different Tire Sizing Systems. • Gives detailed information on Speed-Rating and Load Indexes as well as lug nut torque and tightening sequences. http://tireguides.com/Products/245

  16. On-Scene Information Limited Slip Differential (LSD) Posi-traction One wheel was spinning Movie: My Cousin Vinnie Can narrow type of vehicle Odd mixture of worn tires Suggests an older vehicle Possible alignment problems Stolen items - gasoline Location of gas tank Check footprints @ side of car where gas tank located Estimate from amount taken whether a truck (pickup-SUV)

  17. Mechanical Problems

  18. Mechanical Problems & Vehicle Design Features Fluid leaks @ scene Oil, antifreeze, brake fluid, trans fluid Collect for chemical analysis @ lab

  19. Vehicle Location History Foreign Material on Suspect Vehicle Notice unusual material in tread impression Collect & take to lab

  20. Identifying The Correct Impression

  21. Age of Tire Impression How Long @ Scene How long an object (driven over) has been lying on the ground Complainant may have this information Transferred substance Recently spilled Fluid Knocked over objects Weather conditions prior to offense Help date time of deposit of scene impression

  22. Known Tire Impressions

  23. Known Tire Impressions • Need one full circumference of the tire Complex pitch in modern radials Might miss important accidental characteristics

  24. Taking Tire ImpressionsMethods &Materials needed Large area to make impression Broom Vehicle lift Tire marking crayons Rag to clean dirt from tires Roll of paper towel Large jar of Petroleum Jelly (Vaseline) Gloves Art board 15” x 40” (3 pieces/tire) Lg & sm felt marking pens Magnetic jet black print powder 3” wide magna brush Strips of polyester plastic 12” x 40” to protect impression Scotch tape to attach plastic to art board

  25. Information From Each Tire Photograph Tire Exterior sidewall Tread design Serial number Design, mold & drawing numbers Show up after rubbing w/crayon ID each tire later Manufacturer Tire brand name Tire size Type of tire Summer, etc Construction Radial, bias ply, etc Other numbers Mold, design, etc Wear Number of ribs in design

  26. Recording Known Tire ImpressionsRecording known tire impression Art board is superior to paper Small debris on surface can’t come through Reduces/eliminates wrinkles/tearing common with paper Use gloves to keep board clean 3 pieces of 40” Board sufficient to record 1 full circumference of tire Tread Wear Indicators

  27. Recording Known Tire ImpressionsPetroleum Jelly/Magna Brush Method – 2D Place 2 pieces of art board in path of vehicle travel Tape on reverse side to hold pieces together Mark adjoining pieces appropriately Push car over recording surface Vaseline leaves light brown impression Mark on art board as each tread wear indicator (marked on sidewall) rolls by Mark spaces on art board to correspond to numbers on known tire Tire Wear Indicator Marks Place locations on sidewall

  28. Recording Known Tire ImpressionsPetroleum Jelly/Magna Brush Method – 2D Cover art board in front & behind impression w/paper towel to protect it Clean area of tire that was on the floor when Petroleum Jelly first applied Apply Petroleum Jelly to this area and push car again

  29. Recording Known Tire ImpressionsVaseline/Magna Brush Method – 2D Near end of second art board Stop vehicle Remove 1st piece of art board Add thin coat of Vaseline to tire Place 3rd piece of art board in path of vehicle Continue pushing until known impression is transferred to this 3rd section

  30. Recording Known Tire ImpressionsPetroleum/Magna Brush Method – 2D Dust impression as soon as possible Waiting too long causes defined areas of tread to diffuse into art board surface Brush with magnetic brush @ rt. Angles w/swirling action Avoid dusting clear areas of board Black magnetic Dusting Powder

  31. Recording Known Tire ImpressionsVaseline/Magna Brush Method – 2D Protecting the impression Cover with clear acetate to prevent smearing or damage during transit & comparison process Allows examiner to draw lines during comparison

  32. Recoding Known Tire ImpressionsInking Method I Apply ink to art board for 1 full circumference Fingerprint Ink works Push car (tire) over inked art board This is the inking process Push car over clean strip of white art board to record the impression

  33. Recording Known Tire ImpressionsInking Method II: Transparent Method Ink the tire as in inking method Drive tire over transparent acetate or other transparent media (Mylar) Tape to art board - suitable solid backing Advantages Can be rolled up for storing Unrolled @ later time for comparison Can be compared directly to impression when searching for

  34. Comparing Scene Cast with Acetate Exemplary Overlay

  35. Comparing Scene Cast Actual Exemplar Tire • The area defined by blue tape is the segment of the right rear tire which corresponds with the crime scene cast.