Tyre Pressure & Wear:
For every type of tyre, inflation
pressures are specified by manufacturers. These recommended pressures should be
strictly adhered to since they help to meet the requirements of; Good performance,
heat control, threads kilometers, comfort and better vehicle control. Incorrect
pressure leads to; overheating, unsafe steering, rapid tyre wear.
By considering tyre inflation
pressure is an important parameter, tyre inflation stages results for both
over-inflation and under-inflation are detrimental to tyre operation.
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| Fig 1: Tyre-inflation pressure: stages [1] |
Under-inflation results; excessive flexing of tyre
plies, sidewalls- more heat generation and tyre body damage. Thread edge
wearing, improper vehicle handling noticeable even at low speed about 60kmph.
Over-inflation results; reduction of flexing and
heat generation, wear of centre of tread, tyre tends to puncture when hitting a
pointed object. An under-inflated tyre will merely flex in such a case. [2]
Both the above cases will cause dangerous
steering and control. High speed also causes thee tyre wear and failure. When the
vehicle is running at high speed, there will be high temperature produced by
the distortion of tyre. Such distortion can be reduced by increasing the air
pressure slightly above the normally recommended cold staring pressure.
Tyre wear is a complex phenomenon
that is affected by tyre materials, structures, vehicle dynamics, and road
conditions. In general, uneven tyre wear compromises the life and performance
of tyres, the handling of vehicle, and safety.
Abnormal wear, which is more critical for its safety implications, includes two types: uneven wear and irregular wear. Uneven wear describes non-uniform distribution of wear across tread pattern and irregular wear mainly characterizes circumferential wear vibration. Uneven tyre wear is usually caused by improper alignment, over-inflation, under-inflation or a worn out suspension. Tyres are an extremely important component of a passenger car. Excess wear on the inner or outer edge of the tyre, known as “toe wear” or, in more extreme cases, as “camber wear”, suggests something may be wrong with the wheel alignment. [3]
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| Fig 2: Tyre uneven-wear pattern_wjet [3] |
Toe or camber wear at one end of the strip indicates wheel alignment problem, center wear in the center indicates over-inflation, edge wear at both ends indicates under-inflation, and patch or cup wear around the edge on one side and a sharp edge on the other indicates failed struck or shock. Figure (2) shows the passenger car tyres with the various uneven wear patterns. [3]
 |
| Fig 3: Tyre wear pattern_the-NRMA [4] |
Causes of Tyre Wear:
Most causes of tyre wear are; incorrect inflation, unequal tyres, bleeding of air in tyre, incorrect rotation of tyres, misalignment, out of balance wheel, worn steering mechanism, incorrect caster, camber, or toe angles, excessive braking or violet acceleration, wrong loading, careless driving, toe-out incorrect on turn, defective brakes, overloading and worn kingpins etc. [1]
| Wear Pattern | Causes | Action |
| Center wear | Over-inflated tyre | Adjust tyre pressure to specific load rating per tyre catalogue. |
| Edge wear | Under-inflated tyre | Adjust tyre pressure to specific load rating per tyre catalogue. |
| Side wear | Loss of camber or Overloading | Make sure load does not exceed axle rating. Realign axle at alignment shop. |
| Toe wear | Incorrect toe-in | Align at alignment shop. |
| Cupping | Out of balance | Check bearing adjustment and balance tyre. |
| Flat spots | Wheel lockup and tyre skidding | Avoid sudden stops when possible and adjust brakes. |
[1] A Text Book of Automobile Engineering, By R. K. Rajput.
[2] Automobile Engineering By Ttti, ©Tata McGraw-Hill Education.
[3] Lee, S.W., Jeong, K.M., Kim, K.W. and Kim, J.H. (2018) Numerical Estimation of the Uneven Wear of Passenger Car Tires. World Journal of Engineering and Technology, 6, 780-793.
[4] "Tyre Wear Patterns" by the NRMA.
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