Tyre marks Flashcards
What 6 things can tyre marks tell us?
tyre type
- all terrain
- high-performance
- winter
Make
- michelin
- bridgestone
- goodyear
Model
-optigrip
size of tyre
track width
wheel base
What is the track width?
distance between left and right tyres
What is the wheel base?
the distance between front and rear tyres
Tyre mark evidence
subject to deformation or destruction
- other vehicles
- rain
- wind
ability to find unknown suspects may be limited
- stronger than footwear = PNC/DVLA
- can provide extremely useful intelligence
What are the 4 types of impression.
3D impression
positive impression
negative impression
other impressions
What is a 3D impression?
impressions in soft ground
What is a positive impression?
residue from the tyre is deposited into a surface and remains
What is a negative impression?
tyre removes material from a surface
Give an example of an other impression?
tyre marks on body of victim
What is a treatment for 3D impressions?
cast
What are 3 treatments for wet impressions?
powder
alternative light source
chemical treatment
What is a treatment for dry impressions?
lift
photography in situ
What two features of tyre marks help to identify the size of the vehicle?
track width
scene marks
e.g. 155/70 R13 75 T
What does the 155 represent?
section width (mm)
e.g. 155/70 R13 75 T
What does the 70 represent?
aspect ratio
e.g. 155/70 R13 75 T
What does the R represent?
radial tyre type
e.g. 155/70 R13 75 T
What does the 13 represent?
wheel rim diameter
e.g. 155/70 R13 75 T
What does the 75 represent?
load index
e.g. 155/70 R13 75 T
What does the T represent?
speed rating
Reference tyre mark impressions
tyres should be fitted to suspect vehicles
car/driven/rolled across a section of inked paper onto a section of thick paper
thin layer of vaseline applied to tyre and driven or pushed over thick paper
What are the problems with mould characteristcs?
non unique
- specific to a single tyre mould
- features may therefore be present on numerous tyres
- the sipe is not fully formed
- damaged mold
not conclusive
-does not provide support
What are identifying charactersitcs?
cuts/abrasions
nail or screw head
holes-perforations
trapped material-stones
Conclusion of characteristics
class
-size consistent with scene
sub class
-missing spieling mark consistent with scene
identifying characteristics
- generally consistent
- some missing marks
- may have been lost due to additional wear
