What causes various types of wear?

Apart from checking and maintaining your tyre pressures correctly, there are 2 additional and equally important tasks required by all motorists in the tyre maintenance life cycle:

  1. Tyre rotation – even though this is not possible on vehicles that have different tyre sizes on the rear of the vehicle to the front, on the majority of vehicles on South Africa’s roads, tyre rotation is important. ContiPartner recommends that your tyres get rotated every 10,000 to 15,000 km’s, and if this is too much of an inconvenience, request that your vehicle dealership rotate the tyres each time your vehicle goes in for a service, with the average service intervals currently sitting at 15,000kms.
  2. Wheel Alignment – This must be checked every 10,000 to 15,000 km’s. Some vehicle manufacturers recommend every 10,000 km. Wheel alignment is a sensitive setting on your vehicle and all it could possibly take to upset this setting is hitting a curb. If you hit a curb or pothole it is recommended that you have the alignment checked as soon as possible, as this could have misaligned the wheel(s), it may not pay to wait for the next planned maintenance check

There are several different parameters of alignment on a vehicle, some are adjustable and others not, some will affect tyre life and others not. These parameters are in fact designed into the vehicle as a means of reducing stresses and strains on the vehicle suspension components.

Let us have a look at some of them.

Toe Settings – this is the inward or outward pointing of the wheels in relation to the centre line of the vehicle, and is set to take up any slack in suspension joints (the modern vehicle has very tight tolerances so the settings are far less than they were a number of years ago), so that the tyres will in fact run parallel with one another when the vehicle is travelling in a straight line. Too much toe will dramatically reduce tyre life.

Camber – this is the tilt away from the vertical of the wheel and is designed to place the wheel loading on the larger inner wheel bearings of the front wheel on rear wheel drive vehicles. Too much camber will cause a tyre to wear off on the shoulder, and differing camber angles from one side to another will cause the vehicle to pull to one side.

Caster – the backward tilt of the steering axis, and is designed to give feel on the steering as well as provide steering self centring, so the steering comes back to the straight ahead following a corner. Too little caster will cause the vehicle to wander, and too much will cause heavy steering.

Steering Set Back – the angle where one wheel is ‘set back’ from the other. If a vehicle has a high steering set back, the vehicle will pull toward the side where the wheel is set back. This can often occur when a vehicle has been involved in an accident.

Steering Axis Inclination – this is the tilt from the vertical of the steering axis, and is designed to create a vertical load through the axis, in order to reduce stresses and bending moments on suspension components.

Thrust Angle – this is where the rear wheels are out of line with those on the front, and the vehicle will have a tendency to ‘crab’. Again, this can occur when a vehicle has been involved in an accident.

Scrub Radius – this is the radius created between the centre line of the wheel in contact with the road surface and the line drawn through the steering axis. This can either be positive where the wheel positioning is on the outside of the steering axis line, or negative where the wheel positioning is inside the steering axis. Scrub radius may also be referred to as Roll Radius. Changing the offset of the wheels on the vehicle will change the scrub radius and could severely affect suspension component life, due to increased stresses being placed on them.

In order to preserve the wheel alignment on a vehicle, avoid pot holes, climbing curbs, and parking up against curbs.

Just because your tyres are wearing off smoothly does not mean to say that the alignment is correct. Alignment should be checked every 10,000 to 15,000 kms or 6 months, whichever occurs first, unless you know that you have hit a pothole, or some other object, in which case it should be done immediately as a precaution.