wheels and tyres page 7

1. WWhheeeellss aanndd TTyyrreess
PPaaggee 77

2. LLeeggiissllaattiioonn iiss iinn ppllaaccee ttoo eennffoorrccee
ttyyrree ssaaffeettyy.. TThhee ppoolliiccee hhaavvee
ppoowweerrss ttoo pprroosseeccuuttee ddrriivveerrss tthhaatt
bbrreeaakk tthhee llaaww wwiitthh rreeggaarrdd ttoo ttyyrree
ccoonnddiittiioonn..

3. List below ttyyrree ccoonnddiittiioonnss wwhhiicchh
wwoouulldd bbee ccoonnssiiddeerreedd iilllleeggaall::
• Tread depth less than 1.6mm or not
covering ¾ of the breadth of the tyre
• A bulge in the tyre which is separation of
cords
• Any exposed cords
• Any cuts longer than 25mm or 10% of its
width
• Weight and load ratings incorrect for use
• Inflation incorrect

4. During sseerrvviiccee aa ttyyrree hhaass ttoo bbee
cchheecckkeedd tthhoorroouugghhllyy ffoorr rrooaadd
wwoorrtthhiinneessss,, wwhhaatt ttoooollss aanndd
eeqquuiippmmeenntt aarree nneeeeddeedd ttoo ccaarrrryy
oouutt sseerrvviiccee cchheecckkss oonn aa ttyyrree??

5. • The tyre needs to be off the ground so that
the whole tyre can be checked – so some
form of jack
• Tread depth gauge
• Tyre inflator / gauge
• Torch
• Manual to compare findings – VOSA
regulations

6. An unbalanced wwhheeeell aanndd ttyyrree
aasssseemmbbllyy wwiillll aaddvveerrsseellyy aaffffeecctt aa
vveehhiicclleess hhaannddlliinngg,, ssttaabbiilliittyy aanndd ttyyrree
wweeaarr,, wwhhyy iiss tthhiiss??

7. • Un balanced steered wheels will cause
steering ‘shimmy’, this affects the vehicles
handling and stability and causes uneven
tyre wear.

8. TThheerree aarree ttwwoo wwaayyss tthhaatt aa wwhheeeell
uunniitt ccaann bbee bbaallaanncceedd,, wwhhaatt aarree
tthheeyy aanndd wwhhaatt aarree tthhee
ddiiffffeerreenncceess bbeettwweeeenn tthhee ttwwoo
mmeetthhooddss??

9. DDoonn’’tt wwrriittee tthhiiss ddoowwnn yyeett!!
• Wheels can be balanced either
dynamically or statically
• If a wheel unit was statically out of balance
it would always stop with the heavy spot at
the bottom
• Dynamic balance is when the wheel unit is
run up to a speed and accurate
measurements taken.

10. • Static balance is done at slow speed –
doesn’t give good results on a vehicle
• Dynamic balance is when the wheel is
spun at high speed and accurate
measurements taken

11. DDyynnaammiicc bbaallaannccee iiss bbeetttteerr ssuuiitteedd
ttoo tthhee mmoottoorr vveehhiiccllee;; aadddd aarrrroowwss
ttoo tthhee iilllluussttrraattiioonnss bbeellooww ttoo sshhooww
tthhee ddiirreeccttiioonn ooff tthhee ffoorrcceess aaccttiinngg
oonn tthhee wwhheeeell uunniittss::

12. SSttaattiicc bbaallaannccee
Although the
wheel unit is in
static balance
the wheel would
wobble at high
speeds as the
weights pulled
the steering in
the direction of
the arrows

13. DDyynnaammiicc bbaallaannccee
Dynamic
balance
weights
The dynamic
weights are
positioned
accurately
opposite the heavy
spot of the wheel
unit, this gives
excellent balance
to the wheel unit.

14. Name the ssyymmppttoommss tthhaatt aarree
ccaauusseedd bbyy aa wwhheeeell uunniitt bbeeiinngg oouutt ooff
ccoorrrreecctt bbaallaannccee::
• The steering wobbles ( known as shimmy)
at speeds of around 20 – 50 mph but then
as speed is increased the imbalanced
wheel evens itself out.

15. QQuueessttiioonnss
1. Name 2 reasons for a tyre to be
considered illegal
2. What type of balancing is best suited to a
vehicle and why?
3. Why does the steering shake when a
wheel unit is out of balance?
4. Why does the steering stop to shake a
certain speeds?

16. AAnnsswweerrss
1. Tread less than 1.6mm, bulges, exposed cords,
incorrect tyre, incorrect pressures or cuts
longer than 25mm or 10% of width
2. Dynamic balance – best because the wheel is
balanced whilst being rotated
3. The centrifugal force of the imbalance pulling
the wheel in different directions
4. Because as the imbalance pulls the steering in
one direction when the wheel is rotating fast
enough the imbalance is already in the
opposite position thus canceling out the
shimmy