Get a grip on tyres

TEXT: ELIZABETH CHI, ÅSA LARSBO

Scania lists 250 different different approved tyres for its trucks and buses amongst five premium brands. Not surprisingly, selecting tyres can be confusing. But you can demystify the process by answering just three technical questions, says Christopher Watts, Wheel and Tyre Purchasing, Scania. This process will, according to Watts, lead to tyres that offer “the best combination of handling, service life and fuel economy” for a specific vehicle.

What do you use your vehicle for?

The answer will suggest the right tyre category. All categories are a function of journey length, road conditions and, where road conditions are good, the weather.

In long-haul applications, vehicles tend to travel for long distances at a steady speed on smooth, flat, even roads that have few curves. The focus is on low rolling resistance and fuel economy. With tyres optimised for this type of driving, fuel economy may improve by as much as 6 percent, compared with tyres adapted for driving on regional or urban roads.

For construction and mining applications, however, trucks travel shorter distances on poorer, unpaved or even aggressive surfaces. The focus here is on grip and good resistance to external damage. Timber trucks, for example, operate on and between sites to pick up cargo. Forest roads may be covered with blasted rock – the toughest road conditions anywhere for tyres.

What is your tyre size?

The right tyre size depends on vehicle load weight or vehicle height. For heavy loads, tyres bigger in width and diameter are needed for greater air volume to support the load. If vehicle height is desired − typical for high-volume products that require a lot of space and where weight is a secondary issue − smaller-diameter tyres bring the payload platform lower to the ground.

The trick to achieving the best fuel economy, according to Watts, is to go for the lowest rolling resistance. “Do this by choosing the largest diameter possible for your volume needs and the narrowest tyres for your load needs.”

What is the right tyre pattern for each axle on your vehicle?

Patterns exist for four applications: drive, steer, trailer and all-position. On drive tyres, for example, the pattern is coarser than that on steer tyres in order to achieve a better grip during propulsion and braking. On steer tyres, the pattern optimises scuff resistance, low-speed turning and directional stability for cornering − and thus improves handling.

“Quite often, I see combinations of tyres on vehicles that give sub-optimal performance,” says Watts. If, for example, drive tyres are fitted on steer or trailing positions, this may cause uneven tyre wear, vibration, poorer handling and reduced fuel economy. “A simple guide here is to put drive-type tyres on all non-steered, driven axles and steer tyres in all other positions,” he says. “Trailer tyres should, of course, be used on trailers.”

Buses are the notable exception to the rule, however, says Watts. “Achieving optimal ride quality [reduced noise and better comfort] is the issue, rather than the load factor. So steer-type tyres, which have a smoother profile, can be used all around.”

Proper tyre care is also essential, Watts says. “A correctly inflated tyre lasts longer,” he explains. “Air pressure that is 20 percent too low or too high shortens the useful tyre life by 20 percent. Correct tyre pressure is also vital for safety. Excessively low tyre pressure makes the vehicle unstable.”

Quick guide to choosing the right tyre

Long Haul
Tyres designed to operate on highways and smooth road surfaces comprised of well maintained asphalt or concrete. Very few stops or major speed reductions per100 km. Low rolling resistance.

Regional
Tyres designed to operate on secondary roads, in urban areas, city traffic and frequent stop-and-go traffic. Also suitable for long haulage operation on rough roadways. Medium to high rolling resistance.

Construction
Tyres with high traction and damage resistance for vehicles operating on and between construction sites. High to heavy rolling resistance.

Off Road
Tyres designed for vehicles used almost exclusively on temporary roadways in difficult terrain, typically in mining operation or for military duties. Heavy rolling resistance.

Urban
Tyres designed for city traffic. They have reinforced sidewalls, to resist frequent curb contact, and durability to cope with stop-and-go traffic. Medium rolling resistance.

Winter
Tyres designed to provide the best possible grip and vehicle control on ice and snow as an alternative to long-haul, regional or urban tyres. Medium rolling resistance.