DRIVEN TO DRIVE

Every aspect of a vehicle’s performance and handling rests solely on four very small contact patches and how these patches interact with the road’s surface.  In other words, a driver and a vehicle are only as good as the tires the vehicle is riding on.

There are six things you should know about your tires – three features and three variables.

The features are -

1. Tire Compound
2. Shape or Profile
3. Tire Tread Pattern

The variables are -

1. Tire Pressure
2. Tire Temperature
3. Shock Absorbers and Springs

Tire Compound – All tire compounds stiffen as they get colder.  A tire that is hard and stiff has very little grip and does not handle well.  Consequently, different types of tires are made of different formulations so that they will stay pliable in different temperature ranges.

Don’t feel that you are still getting your money’s worth because your tires still have tread after 160,000 km (100,000 miles).  If a tire’s tread is appearing to be lasting forever, then you may have a problem – the chemical compound of the tire material may have changed and hardened beyond usefulness, and is bordering upon being dangerous.

Shape or Profile – Regardless of whether the tire is wide or narrow, the same area of tire is in contact with the road.  If the tire is narrow then the contact patch will be elongated.  If the tire is wide then the contact patch will also be wide.

Wide tires give good traction while cornering on a good clean road surface, but give a firmer ride and are more prone to wandering on irregular road surfaces.  Narrower tires give a smoother ride and handle far better in poor conditions such as rain or snow.

Tire Tread – The familiar tread pattern seen on tires serves one purpose and one purpose only – to aid traction in very wet conditions.  On dry road surfaces, tire tread serves no purpose what-so-ever.

In the wet, water is channelled into the grooves thus allowing the tire to make contact with the road.  The water is then released as the tire rotates.  If this didn’t happen, the tire would tend to ride up on a cushion of water and would be extremely susceptible to skidding and sliding.  This effect is known as hydroplaning.

Even with a legal amount of tire tread, there can still be sufficient water on the road surface to build up under the tread reducing the actual amount of tire in contact with the road surface.

The tread on winter tires may give some small amount of grip in freshly fallen snow but the main advantage is to help prevent snow from clinging to the tire.  As the tire rotates, snow is released from the tread and the tire is clear to grip the surface on its next time rotation.

None of these features mean anything if the tire pressure is incorrect, or if the tire is not at its working temperature, or if the vehicle has worn shock absorbers or springs.

Tire Pressure – A couple of pounds difference in tire pressure can change the way a vehicle handles.  Tires will come with their own manufacturer’s recommended tire pressures, but this may have to be varied according to the particular vehicle they are mounted on, how much of a load the vehicle is carrying and whether the tires are mounted on the front or on the rear of the vehicle.

If the tire pressure is too low, you will soon wear out the outside edges of the tires and possibly damage the side walls of the tire.  Also, the vehicle will have increased resistance to driving on the road and the steering will feel heavy, especially in corners.  Alternatively, if the tire pressure is too high, you will wear out the centre of the tires and vehicle may experience poor grip, especially in corners.

Tire pressure falls with temperature, therefore in cold seasons, it is even more important that you regularly check your tire pressures.

Tire Temperature – Tires warm up to their operating as you drive and this temperature is very important.  When a tire reaches its operating temperature it achieves optimum grip.

If the tires are cold, expect poor grip which will be especially noticeable when stopping and cornering.  If you have tires which are unsuitable for the cold season, they may never reach their optimum temperature, and therefore you will run the risk of driving a vehicle with poor traction. See Tires and Temperature

The pressure can increase as much as much as 20 Kpa (3 lbs per sq in) in a warm tire.  Check tire pressures weekly or anytime you suspect that a tire is low.

Shocks Absorbers and Springs – If you have worn-out shock absorbers, your vehicle will drive like a giant pogo stick, bouncing all over the place.  If the springs are worn out, expect a very jolty ride, and on rough road surfaces, expect the suspension to actually ‘bottom out’.  That is, the suspension frame will hit the underside of the vehicle.  In either case, the ability of a tire to grip the road is limited if the tires are bouncing up and down due to poor shock absorbers or springs.

While shock absorbers and springs are a major part of a vehicle’s suspension and are obviously important, what is crucial is how these two components work together.  The shock absorbers serve to temper the springs from overreacting – that is, to modulate their compression and expansion.  If the shock absorbers are not suitably matched to the springs, their ability to modulate the spring’s actions will be wasted.  Some after-market suppliers sell springs and shocks as a kit thus ensuring that the owner gets a matched set.