Forensic Tire Impressions

Chapter 20Chapter 20CRC Press: Forensic Science, James CRC Press: Forensic Science, James

and Nordby, 3rd Editionand Nordby, 3rd Edition 11

Forensic ScienceForensic ScienceAn Introduction to Scientific and An Introduction to Scientific and

Investigative TechniquesInvestigative Techniques

Stuart H. James and Jon J. NordbyStuart H. James and Jon J. Nordby

22Chapter 20Chapter 20CRC Press: Forensic Science, James CRC Press: Forensic Science, James

and Nordby, 3rd Editionand Nordby, 3rd Edition

Chapter 20Chapter 20

Forensic Tire Tread and Tire Forensic Tire Tread and Tire Track Evidence Track Evidence

Chapter Author: William J. BodziakChapter Author: William J. Bodziak

Presentation created by Greg Galardi, Peru, NebraskaPresentation created by Greg Galardi, Peru, Nebraska

Edited by Stuart H. James, Fort Lauderdale, Florida andEdited by Stuart H. James, Fort Lauderdale, Florida and

Dan Mabel, Richmond, VirginiaDan Mabel, Richmond, Virginia



Forensic Tire Tread and Tire Track Forensic Tire Tread and Tire Track EvidenceEvidence

Tire impressions reflect the tread Tire impressions reflect the tread design and dimensional features of design and dimensional features of individual tires on a vehicleindividual tires on a vehicle

Tire Tracks are relational dimensions Tire Tracks are relational dimensions between two or more tires: tracks can between two or more tires: tracks can be used to determine the wheelbase of be used to determine the wheelbase of the vehiclethe vehicle



Original Equipment Tires, Original Equipment Tires, Replacement Tires and Tire Replacement Tires and Tire

ConstructionConstruction• Original Equipment Tires - tires sold on new Original Equipment Tires - tires sold on new

equipment equipment • Replacement tires – those used to replace Replacement tires – those used to replace

worn or damaged tiresworn or damaged tires• Most tires today are of radial ply Most tires today are of radial ply

constructionconstruction• Tires are composed of liner, sidewall rubber, Tires are composed of liner, sidewall rubber,

beads, belts and tread rubberbeads, belts and tread rubber



Tread Nomenclature and Tread Nomenclature and Sidewall InformationSidewall Information

• Tire treads are composed of design Tire treads are composed of design elements separated by grooveselements separated by grooves

• Grooves which run across a tire are Grooves which run across a tire are called slots or transverse groovescalled slots or transverse grooves

• Tread wear indicators – raised areas Tread wear indicators – raised areas which indicate tread wearwhich indicate tread wear




• Department of Transportation number, Department of Transportation number, known as DOT number – consists of:known as DOT number – consists of:

• DOT AC L9 ABCD 4901DOT AC L9 ABCD 4901• DOT impressionDOT impression• Plant code and manufacturerPlant code and manufacturer• Date of manufactureDate of manufacture• Tires made after January 1, 2000 have Tires made after January 1, 2000 have

four numbers in last group, while prior four numbers in last group, while prior to that there are three numbersto that there are three numbers




• Retread tires – have slightly different Retread tires – have slightly different numbersnumbers

• DOTR YPY 1201DOTR YPY 1201• DOTR – Department of Transportation DOTR – Department of Transportation

retreadretread• YPY – Manufacturer retreadYPY – Manufacturer retread• 1201 – date and year of manufacture1201 – date and year of manufacture




Common tire size designation includes:Common tire size designation includes:• PP 195195//6565 RR 1515• P – passenger tireP – passenger tire• 195 – approximate width in millimeters195 – approximate width in millimeters• 65- aspect ratio65- aspect ratio• R – radial tireR – radial tire• 15 – rim diameter in inches15 – rim diameter in inches



Noise TreatmentNoise Treatment

• Stress Cycle - Under load of a vehicle, Stress Cycle - Under load of a vehicle, rotating tire goes through stress rotating tire goes through stress

• Contact Patch – portion of tire touching Contact Patch – portion of tire touching groundground

• Noise treatment – tire industry created Noise treatment – tire industry created tire designs that vary the size (pitch) tire designs that vary the size (pitch) design elements of tire. This reduces or design elements of tire. This reduces or controls noise emitted by tire controls noise emitted by tire



Noise TreatmentNoise Treatment

• Mixture of three design elements, small Mixture of three design elements, small (S), medium (M) and large (L) allow (S), medium (M) and large (L) allow manufacturers to change size of tires manufacturers to change size of tires and minimize noiseand minimize noise

• Noise treatment is different on opposite Noise treatment is different on opposite sides of tiresides of tire



Tread Wear IndicatorsTread Wear Indicators

• Tread Wear Indicator, or known as a Tread Wear Indicator, or known as a wear bar, is a raised rubber bar 1/16 of wear bar, is a raised rubber bar 1/16 of an inch above base of grooves of tirean inch above base of grooves of tire

• DOT requires all tires contain a DOT requires all tires contain a minimum of six tread wear indicatorsminimum of six tread wear indicators

• As tread wears down on tire, these As tread wears down on tire, these become noticeable and indicate tire become noticeable and indicate tire needs replacement – these indicators needs replacement – these indicators can be retained in 3-D impressionscan be retained in 3-D impressions



Retread TiresRetread Tires

• Retread tires are primarily used for Retread tires are primarily used for commercial or fleet vehicles in United commercial or fleet vehicles in United StatesStates

• Two types of retread processes:Two types of retread processes:• Mold Cured ProcessMold Cured Process• Pre-Cured ProcessPre-Cured Process

• Some retread tires have valuable Some retread tires have valuable individual characteristics which individual characteristics which provide information to the examinerprovide information to the examiner



Tire Track EvidenceTire Track Evidence

Tire track evidence consists ofTire track evidence consists of::

• Tire track widthTire track width• Wheelbase dimensionsWheelbase dimensions• Turning diameterTurning diameter• Relative positions of turning tracksRelative positions of turning tracks




• Track Width (Stance) – measurement Track Width (Stance) – measurement made from one center of one wheel to made from one center of one wheel to opposite center of wheelopposite center of wheel

• Front wheels turning produce Front wheels turning produce unreliable measurementsunreliable measurements

• Rear wheels accurately record turnsRear wheels accurately record turns




• Wheelbase – measurement of center of Wheelbase – measurement of center of hubs of front wheels to center of hubs hubs of front wheels to center of hubs of rear wheel of rear wheel

• Normally these measurements are not Normally these measurements are not present at crime scenespresent at crime scenes




• Turning Diameter – Diameter of circle a Turning Diameter – Diameter of circle a vehicle makes when its steering wheel is vehicle makes when its steering wheel is fully turned – pertains to front wheels onlyfully turned – pertains to front wheels only

• Turning diameter is measured by (B Turning diameter is measured by (B squared/A) + A, where:squared/A) + A, where:

• B = distance between two points ( x and x’) B = distance between two points ( x and x’) on turn circleon turn circle

• A = distance between outer margin and a mid A = distance between outer margin and a mid point between x and x’point between x and x’



Tire Positions in a TurnTire Positions in a Turn

• When vehicle moves in straight path, When vehicle moves in straight path, only rear tire tracks are availableonly rear tire tracks are available

• When a vehicle turns, rear and front When a vehicle turns, rear and front tires rack separatelytires rack separately

• Important to understand and document Important to understand and document at crime scenesat crime scenes



Recovery of EvidenceRecovery of Evidence

Tire impressions must be:Tire impressions must be:• Photographed from all angles with and Photographed from all angles with and

without measurement tool (ruler)without measurement tool (ruler)• Cast – a 3 foot impression requires 15-25 Cast – a 3 foot impression requires 15-25

pounds of dental stonepounds of dental stone• Measured – width, length and depthMeasured – width, length and depth• Direction of travel noted Direction of travel noted • Impressions made if possible, andImpressions made if possible, and• Pictures of the source (tire) must be Pictures of the source (tire) must be

included for comparisonincluded for comparison



Known Tires and ExemplarsKnown Tires and Exemplars

• Tire tread examinations compare the Tire tread examinations compare the tire impressions recovered from scene tire impressions recovered from scene with tires taken from a known vehiclewith tires taken from a known vehicle

• Two categories of tires:Two categories of tires:• Suspect - Vehicle of suspectSuspect - Vehicle of suspect• Elimination - Vehicles of police, Elimination - Vehicles of police,

ambulance, etcambulance, etc• All tires should be seized from suspect All tires should be seized from suspect

vehicle for comparisonvehicle for comparison



Tire Impression, the Examination Tire Impression, the Examination Process, and ConclusionsProcess, and Conclusions

• Tire impressions are resulting transfer Tire impressions are resulting transfer of tread detail of a tire against a of tread detail of a tire against a substratesubstrate

• Impressions can be three or two Impressions can be three or two dimensionaldimensional

• Forensic examination begins with Forensic examination begins with visual comparison and elimination of visual comparison and elimination of tires which do not match impressiontires which do not match impression



Tire Impression, the Examination Tire Impression, the Examination Process, and ConclusionsProcess, and Conclusions

• Forensic examination continues with Forensic examination continues with full circumference test impressionsfull circumference test impressions

• Impressions are superimposed on Impressions are superimposed on known impression over cast or original known impression over cast or original tiretire

• Other factors to be evaluated are tread Other factors to be evaluated are tread design, tread dimension, noise design, tread dimension, noise treatment, wear features and random treatment, wear features and random individual characteristicsindividual characteristics

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Forensic Tire Impressions