wheels and tyres page 5

1. Wheels and Tyres
Page 5

2. Tyres are manufactured to
withstand certain loads. The
load index is a numerical code
which indicates the capacity of a
tyres load carrying ability.

3. The table below is a load index
table.

4. Competition
• What is the load capacity of a tyre with a
load rating of……..
• 110?
• Answer 1060kg
• That is 1.06 tonnes

5. What would be the possible effect
of using a tyre with too low a load
rating?
• The tyre would be over loaded which could
cause separation of the carcass
• This could mean a blow out

6. The speed rating table is similar to
the load rating but the code prefix is
a letter not a number. The speed
rating of a tyre denotes its ability to
safely handle speed.

7. Below is a speed rating table
The letters get
higher as the
speed goes up
except for the
letter ‘H’. The H
stands for High
speed, the V
for Very high
speed

8. What would be the possible effect
of using a tyre with too low a speed
rating?
• The tyre could overheat and fail in service,
this could prove to be very dangerous

9. On some tyres the letters TWI are
placed on the tyre shoulder, what
do the letters stand for?
• Tread wear indicator
• A tread wear indicator can be found at the
bottom of the tread, they allow a quick
visual inspection of the tyre to ascertain
serviceability

10. Questions
1. A vehicle has a gross vehicle weight of
3000kg and needs a tyre that can
withstand speeds of 180 kph, what tyre
would you recommend?
2. Why is it illegal to use a tyre with too low
a load index?
3. Why is it illegal to use a tyre with too low
a speed rating?
4. A tyre which is worn down to the tread
wear indicators would tell you what?

11. Answers
1. You would need a tyre of at least a load
rating of 98 or over and a speed rating of
S or over
2. Tyre can be over loaded and fail
3. Tyre can be over heated and fail
4. If tread wear indicators are level with the
tread it visually lets you know that the
tyres are getting down to the last 2-3 mm
of tread and should be measured using a
depth gauge