Wheels and Tyres Wheels and Tyres

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Tyres are manufactured to Tyres are manufactured to withstand certain loads. The withstand certain loads. The

load index is a numerical code load index is a numerical code which indicates the capacity of a which indicates the capacity of a

tyres load carrying ability. tyres load carrying ability.

The table below is a load index The table below is a load index table. table.

Competition Competition

• What is the load capacity of a tyre with a load rating of……..

• 110?

• Answer 1060kg

• That is 1.06 tonnes

What would be the possible effect What would be the possible effect of using a tyre with too low a load of using a tyre with too low a load

rating?rating?

• The tyre would be over loaded which could cause separation of the carcass

• This could mean a blow out

The speed rating table is similar to The speed rating table is similar to the load rating but the code prefix is the load rating but the code prefix is

a letter not a number. The speed a letter not a number. The speed rating of a tyre denotes its ability to rating of a tyre denotes its ability to

safely handle speed. safely handle speed.

Below is a speed rating tableBelow 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

What would be the possible effect What would be the possible effect of using a tyre with too low a speed of using a tyre with too low a speed

rating? rating?

• The tyre could overheat and fail in service, this could prove to be very dangerous

On some tyres the letters TWI are On some tyres the letters TWI are placed on the tyre shoulder, what placed on the tyre shoulder, what

do the letters stand for?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

Questions 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?

Answers 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 fail3. Tyre can be over heated and fail4. 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