The document discusses tyre sizes and aspect ratios. It explains that tyre sizes are denoted by a series of numbers on the sidewall. Today, tyres often have different widths and heights, and this size differentiation is expressed as an aspect ratio. The aspect ratio is the ratio of the tyre's height compared to its width, expressed as a percentage. The document provides an example tyre size and explains what each number in the size designation represents, such as width, aspect ratio, rim diameter, load index, and speed rating. It also discusses causes of different tyre wear problems like under inflation and over inflation.

1. WWhheeeellss aanndd TTyyrreess
PPaaggee 66

2. The tyre size iiss ddeennootteedd bbyy aa sseerriieess
ooff nnuummbbeerrss oonn tthhee ssiiddeewwaallll ooff aa ttyyrree..

3. WWhheenn ttyyrreess wweerree iinn tthhee eeaarrllyy
ddaayyss ooff ddeessiiggnn,, aa ttyyrreess hheeiigghhtt
wwaass ssiimmiillaarr iinn ssiizzee ttoo iittss wwiiddtthh..
TThhaatt iiss ttoo ssaayy iiff aa ttyyrree wwaass 117755
mmiilllliimmeetteerrss wwiiddee,, iitt wwaass 117755
mmiilllliimmeetteerrss hhiigghh..

4. TTooddaayy iitt iiss ccoommmmoonn ffoorr aa ttyyrreess
wwiiddtthh aanndd hheeiigghhtt ttoo bbee ddiiffffeerreenntt..
TThhee wwaayy mmaannuuffaaccttuurreerrss ddiissppllaayy
tthhiiss ssiizzee ddiiffffeerreennttiiaattiioonn iiss ttoo
eexxpprreessss iitt aass aa rraattiioo..

5. What iiss tthhee nnaammee ggiivveenn ttoo tthhiiss
rraattiioo??
• It is called the aspect ratio

6. TThhee tteerrmm aassppeecctt rraattiioo iiss tthhee rraattiioo
ooff tthhee ttyyrreess hheeiigghhtt wwhheenn
ccoommppaarreedd ttoo iittss wwiiddtthh;; tthhiiss iiss
eexxpprreesssseedd aass aa ppeerrcceennttaaggee..

7. LLaabbeell tthhee ttyyrreess bbeellooww::
What aspect ratios fit the tyres below?
Tyre with 100%
aspect ratio
Tyre with 30%
aspect ratio

8. What is meant by tthhee ffoolllloowwiinngg ttyyrree
ssiizzee,, 117755// 7700 RR 1144 8800 SS
• In pairs have a go at working out what
each number means

9. 117755
• The first number – the 175
• Is the sectional width of the tyre measured
in millimeters

10. TThhee 22nndd nnuummbbeerr tthhee 7700
• Is the aspect ratio
• This means the height is 70% of the width

11. TThhee RR mmeeaannss……
• The tyre is a radial tyre
• This means the plies run at 90 degrees to
the bead

12. TThhee 1144 iiss……
• The rim diameter measured in inches

13. TThhee 8800 iiss……
• The load index
• This means this tyre is able to cope with
loads up to 450 KG (almost half a tonne,
which is 500KG)

14. TThhee SS iiss……
• The speed rating
• An S speed rating means that the tyre is
capable of speeds up to 180 KPH or 113
MPH
• Plenty fast!!!!

15. Some ttyyrreess hhaavvee aa ssiizzee wwhhiicchh iiss
ddiissppllaayyeedd lliikkee tthhiiss …… 117755 RR 1144,,
wwhhaatt ddooeess tthhiiss mmeeaann aabboouutt tthhee
aassppeecctt rraattiioo??
• It means the aspect ratio is said to be
‘normal’ which is said to be approx 82%

16. List the faults wwhhiicchh hhaass ccaauusseedd tthhee
ffoolllloowwiinngg wweeaarr pprroobblleemmss
Under inflation Over inflation Excess camber

17. QQuueessttiioonnss
1. What is meant by the term aspect ratio?
2. What unit of measurement is the wheel
rim usually measured in?
3. What unit of measurement is the tyre
width measured in?
4. A tyre with excess wear in the centre
would indicate what?
5. A tyre with excess wear on both outer
edges would indicate what?

18. AAnnsswweerrss
1. The aspect ratio is the percentage the
height of the tyre is compared to the
width, expressed as a ratio
2. Inches
3. Millimeters
4. Over inflation
5. Under inflation