Tyres part 2

Tread• To give the best overall grip in all weather.

• Specialist tread patterns – snow and mud – racing slicks – racing wets – off road etc.

• Road tyres are a compromise between wet grip and dry grip.

• The grooves in the tread are to disperse water from the road to enable maximum contact with the surface.

Aquaplaning or Hydroplaning a

• If the tread is worn or the tyre is fitted incorrectly, it will be unable to shift standing water efficiently. The tyre will then ride on the surface of the water and the vehicle will lose traction, drive and control. Braking is impossible and only makes matters worse.

Standard tread• Standard road tyres, give good,

efficient and uncomplicated performance for road use under normal driving conditions.

The central channel is a recent innovation. It gives water a shorter route to disperse as if the tyre was really 2 narrow tyres.

M&S

• Mud and Snow (knobblies), mostly for off-road use often preferred in the winter months in rural areas.

Grip on tarmac is compromised in favour of grip off-road. Road noise is distinct and loud.

Snow Tyres

• Popular in the northern European countries that have snow for months and don’t salt their roads.

Notice the steel spikes and saw edges to the tread. Good grip can be achieved even on frozen lakes and pack ice.

Unidirectional

• This tread is used on higher performance vehicles.

They improve forward acceleration and stopping distances are shortened. They are quieter running and improve water dispersal. They must be fitted correctly, to rotate in the designed direction only. (arrows on wall indicate direction of rotation)

normal unidirectional

• Asymmetrical tyres

The tread on an asymmetrical tyre has a wider tread to the inner side for greater water dispersal, and a narrower edge to the outside for greater grip in the dry. The words “inner side” are written on the inner wall to prevent incorrect fitting.

Q. Why are they fitted this way?

Inflation

• The correct inflation of a tyre is crucial to performance and long life.

• Over inflated tyres have less surface area in contact with the road and wear more in the middle.

• Under inflated tyres also have less rubber on the road, loss of grip on corners. They wear more the outer edges quickly and damage the walls.

Wide v narrow

• It is a popular misconception that a wide tyre gives you more rubber on the road. In fact it makes NO difference to the over all coefficient of friction.

Get you head round this:- If the car weighs the same and the tyre is inflated the same the roundness of the tyre will flatten or deflect the same amount and it is this that dictates the “rubber to road ratio” not the width of the tyres but the compression of the air within it. So if you want more grip – carry a passenger.

Better in a straight line

Better in cornering

Balancing

• A wheel needs to be balanced to prevent “tramping” an up and down motion while the wheel rotates. This will cause poor handling, vibration through the steering wheel and tyre wear.

Things that effect the balance are:-

Valves, rim defects, tyre construction variants, dirty inner wheels (stuck mud) and loss of balancing weights.

Other defectsBulge :- weak wall from curbing, or perishing

Flat spots can occur because of harsh breaking or poor balancing.

Delaminating of remould tyres.

A footnote on cross-ply v Radial

• Comparison of Radial vs. Cross-ply performance

• This little table gives you some idea of the advantages and disadvantages of the two types of tyre construction. You can see the primary reasons why radial tyres are almost used on almost all the world's passenger vehicles now, including their resistance to tearing and cutting in the tread, as well as the better overall performance and fuel economy.

Cross-ply Radial

Vehicle Steadiness

Cut Resistance - Tread

Cut Resistance - Sidewall

Reparability

Self Cleaning

Traction

Heat Resistance

Wear Resistance Flotation

Fuel Economy