Wheels and Tyres

Page 4

3 groups, each group to

research a given topic and feed

back to the group

Group 1 characteristics of a radial ply tyre

Group 2 characteristics of a cross ply tyre

Group 3 reasons why cross ply and radial

ply tyres cant be mixed in some

circumstances

Characteristics of radial and

cross ply tyres are very

different. So much so that it is

illegal to mix them in differing

layouts.

State characteristics of radial tyres:

• Lower rolling resistance so fuel

consumption is improved

• Better handling than a crossply tyre

• Approximately 80% longer life than a cross

ply tyre

State characteristics of cross ply

tyres:

• Lighter steering at slow speeds

• Don’t provide good adhesion when

cornering when compared to radial ply

tyres – vehicle will drift easier with cross

ply tyres

Which tyre is the most desirable for

use on modern vehicles and why?

• Radial ply tyres are more desirable

• Better road holding

• Better fuel consumption

• Better life expectancy

Below is a mix of tyres on various

vehicles, state whether the tyre

combinations are legal or illegal:

Legal or illegal?

Illegal

Legal or illegal?

Illegal

Illegal or legal?

Legal

Legal or illegal?

Legal

This is an odd combination, this is legal because of the number of tyres

on the rear axle giving more surface area in contact with the road surface,

so less likely to get over steer. It is illegal to mix cross plies and radial on

the rear axle because as the radial tyres deflect the cross ply tyres will be

over loaded.

State why it is considered

dangerous to mix radial and cross

ply tyres in certain combinations:

• Because of the steering and road holding

characteristics between the two tyres

• Radial ply tyres are better at road holding than

cross plies

• Understeer is more desirable than over steer, so

if the two are to be mixed the radials must be

fitted to the rear

Questions

1. What tyres are considered to be the best?

2. Name 2 advantages of radial ply tyres over cross ply tyres

3. Why is it illegal to mix cross ply and radial ply tyres on the same axle?

4. If you have 2 radial ply tyres and 2 cross ply tyres how can they all be fitted to the vehicle legally?

5. What steering situation is considered to be the most desirable under or over steer, and why?

Answers

1. Radial ply tyres

2. Better fuel efficiency, last longer, better road holding

3. Because of the different handling characteristics of the two types of tyre would make it unsafe

4. Radials to the rear, cross plies to the front

5. Under steer is most desirable because it is deemed easier to control – so is safer