Tyre mark impression evidence-Will

Question 1

what is the bead?

Answer 1

holds the tyre onto the wheel rim

reinforced with a steel band encased within the sidewall

Question 2

what is the sidewall?

Answer 2

provides structural rigidity, deforms to absorb impact

standard tyres=will collapse when punctured

run-flat tyres=designed to retain rigidity when air pressure lost and allow continued driving

Question 3

what are tread blocks?

Answer 3

make up majority of the tyre tread

used to improve traction and allow efficient efflux of water

designed to minimise noise and dissipate heat

Question 4

what is the sipe?

Answer 4

improves grip in the wet on ice and snow

increases the number of edges presented

allows more flexibility in the tyre blocks which although not energy efficient does improve heat dissipation

Question 5

what are dimples?

Answer 5

increase surface area of the tyre allowing improved cooling

Question 6

what are ribs?

Answer 6

circumscribe the tyre

increases lateral grip allowing more stable cornering

Question 7

what are grooves?

Answer 7

a void to allow the efficient channelling of water to the rear of the tyre

Question 8

groove void ratio

Answer 8

the ratio of open space to rubber in the tread

low void=racing tyre
standard=general purpose suitable for dry and wet conditions
high void=off road tyre

Question 9

tread wear indicators

Answer 9

raised area within the tread

Question 10

what is the legal tread wear?

Answer 10

1.6mm across central 3/4 of tyre

Question 11

compounding - tyre construction

Answer 11

bringing together and mixing of tyre components - rubber and other additive materials

brought together and mixed using large rotors

shearing action generates considerable heat which can cause premature chemical reaction of components

whole machine must be cooled

after mixing the compound is fed into an extruder where thick sheets are formed

these are powered and stored for further processing

Question 12

tyre rubber

Answer 12

tyre rubber is a mixture of synthetic and natural elastomers, carbon and sulphur

the synthetic rubber can be varied allowing the designer to produce softer or harder compounds

Question 13

constituents of tyre

Answer 13

rubber
carbon
reinforcing material
plasticisers
vulcanisation chemicals
antioxidants

Question 14

calendering - tyre construction

Answer 14

some of the tyre constituents are formed directly from extruded material

tread areas may be different compound to side walls

most tyres will include reinforcing ply layers and these are formed by a process known as calendering

rubber compound is forced around fabric or steel to form ply material

Question 15

carcass assembly - tyre construction

Answer 15

takes place around a tyre construction drum

components brought together and joined

• steel beads
• inner lining
• inner play
• steel belting
• outer ply
• sidewalls
• tread

forms what is known as a green tyre

Question 16

curing - tyre construction

Answer 16

green tyre places in a mold and heated to 170 degrees

a bladder within the mold is inflated and subjects the tyre to 25 ATM

this forces the tyre to adopt the shape of the mold, become fully airtight and most importantly causes a chemical change in the rubber

Question 17

Vulcanisation - tyre construction

Answer 17

the addition of sulphur or other vulcanising reagents will form cross links between strands

by anchoring the strands to each other the properties are radically altered and the mass becomes more elastic and harder

altering the amount of vulcanising agent and length of vulcanisation will affect hardness and elasticity

Question 18

what are the 3 tyre designs?

Answer 18

astmmetric=increased lateral stability

unidirectional=superior grip and braking

symmetrical

Question 19

noise treatment

Answer 19

use variable block sizes and patterns

may induce destructive interference

can be designed by computer to test relative noise of multiple pattern types

most common = variable pitch lengths

Question 20

what does 155/70 R13 75 T stand for?

Answer 20

155=section width
70=aspect ratio
R= radial tyre type
13=wheel rim diameter
75=load index
T=speed rating

Question 21

aspect ratio

Answer 21

height of the sidewall/section width
measured unloaded at maximum recommended pressure
standard = 70

Question 22

what does DOT stand for?

Answer 22

Department of Transportation

Question 23

3D impression

Answer 23

impression in soft ground
most prolific

cast using dental stone

Question 24

wet origin impressions

Answer 24

powders = aluminium, bristol black
alternative light source
chemical treatment
-blood = KM, LMG, Luminol
-mud=thiocyanates
-physical developer=paper or cardboard media

Question 25

dry impressions

Answer 25

powders=aluminium, bristol black
alternative light source
chemical treatment 
-bromophenol blue may work well with alkaline marks
lifting could be viable

Question 26

3 examples of environmental deformation

Answer 26

weather
other vehicles
human/animal activity

Question 27

track width

Answer 27

distance between the centre point of one tyre contact patch to that of the opposing tyre

Question 28

4 examples of treadmark databases

Answer 28

treadmate
tire global information
tireprint
tire guides

Question 29

how to work out diameter?

Answer 29

circumference/Pi

Question 30

reference marks

Answer 30

tyre should be on vehicle

weight of vehicle should cause same deformations seen un the scene mark

car drive/rolled across section of inked paper and onto a section of thick paper

thin layer of vaseline applied to tyre and driven or pushed over thick paper
-bristol black powder used to develop tyre mark image

Question 31

class characteristics

Answer 31

repeatable characteristics shared by all tyes of the same type

Question 32

reference comparison

Answer 32

correlation

imaging techniques - overlay software

physical overlay - transparency materials

Question 33

sub class characteristics

Answer 33

features resulting from the variability of individual molds

not unique but discriminating

Question 34

identifying characteristics

Answer 34

damage events caused by random process