2008.09.23

Hannover, September 2008. Commercial vehicle tyres have long been known to have an impact on the operating costs of a commercial vehicle. To be sure, the rising price of crude oil, the road toll for trucks and other operating costs have shifted the position of the tyre in daily operating cost standings.

Ever since trucks have been around, vehicle owners have all been aware that tyres have a major influence on operating costs. Commercial vehicle tyres have thus always been a focus of attention for users and operators. A tyre’s mileage performance and the second-life value of its carcass were constantly praised to the high heavens. Regrooving and retreading – like mileage performance – always captured the most interest. As a consequence of looking at things this way, commercial vehicle tire shoppers tended to judge the tyres by their geometry. The more wear volume the tyre had, the longer the buyer could hope to be able to use it.

The commercial vehicle tyre industry responded by wrapping the carcasses in broad-based, deep treads. The tyre was optimized in such a way as to spread wear out evenly over as much of the material as possible.

The same old song: Mileage performance, mileage performance ....

Many a commercial vehicle manufacturer never tired to draw their customers' attention to the considerable impact that a tire’s rolling resistance had on the economic efficiency of vehicles and fleets. And although backed up by scientific studies, customers tended to regard the manufacturers' observation as nothing more than a friendly reminder. Every motorist knows from personal experience how hard it is to determine exactly what tires contribute to the car’s overall cost-efficiency. To be sure, owners of trucks and fleets are in a better position to gather internal controlling data. The many external factors of influence nonetheless make it difficult to obtain a clear and watertight picture. These factors include weather, driving style and load differences, to cite just a few.

In assessing the cost-efficiency of a commercial vehicle, there are four factors that are influenced to a considerable degree by the type of tire used: Its reliability and the carcass’s retreading value, the tyre’s mileage performance and – far and away the most important – the cumulative rolling resistance of all of a vehicle’s tyres.

Four factors are at play that influence the sum effect of the tyres

The reliability of a tyre determines whether cost-efficient motoring is at all possible. It can therefore be regarded as a basic prerequisite. A tyre’s retreading potential is a measure of the reserves the tyre makes available to the customer. For years now, Continental AG has defined a continued improvement in commercial vehicle tyre retreadability as a development goal. In its latest-generation tyres – the HTR 2 trailer tire, for example – an optimized triangular belt and steel cord bead are used alongside the usual steel cord carcass.

A continuous improvement in the tyre's wear pattern has also been on the Hanover tyre developers' agenda for years. However, whereas in earlier years developers collaborated closely with large fleets in conducting lengthy field testing that would, hopefully, shed light on the fruits of their labor, nowadays efficient simulations are capable of providing significant results in just a few hours and days. As a result, the tyres sold to customers are designed in such a way that its material does in fact wear as evenly as intended, so that at the end of the first tyre life, there is hardly any superfluous material left on the carcass.

Engineers have been at work almost as long to reduce rolling resistance. Mathematically it is easy to prove that rolling resistance contributes more than the other two factors toward optimizing cost-efficiency. Tires account for roughly 40% of tractive resistance on a typical semitrailer with its average of 12 tires, proceeding at a driving speed of negligible aerodynamic significance. The diesel consumption of such a semitrailer nowadays is approx. 30 liters/100 km. This means the tires’ share of consumption works out to about 12 liters/100 km. At this point, at the very latest, it becomes evident that in view of current fuel prices – and the expectation that these will continue to rise – there is now a new demand: that of minimizing rolling resistance as much as possible. With diesel prices currently around €1.50/liter, a one-percent optimization in rolling resistance has roughly the same effect as a 10-percent improvement in mileage performance.

For many years now Continental AG has played a leading role in optimizing rolling resistance. For a number of reasons, the efforts were aimed primarily at reducing the weight of the tyre, which ultimately led to a direct improvement in rolling resistance.

In the new generation of products ushering in the HTR 2, new technologies made it possible to achieve quantum leaps unthinkable years back. An innovative belt design, for example, resulted in more tire tread volume, meaning more material. Rolling resistance has, nonetheless, been reduced by 5%, giving the tyre an edge on the competition. Underpinning this is an intelligent tread design that optimizes the agility of the tire to such an extent that here as well, further reductions in rolling resistance could be realized.

The new game plan: Rolling resistance, rolling resistance ...

A tyre's inflation pressure plays a major role in day-to-day operations. A loss in a tyre’s service pressure triggers a rise in rolling resistance. This results in increased fuel consumption and a narrower margin of tire safety. Continental AG makes use of its patented AIRKEEP® technology in new products. The special inner liner compound this technology employs reduces air permeability by 50%. Diffusion losses between service checks are thus minimized. A positive side effect is an improvement in the wear pattern, which is much more uniform in properly inflated tyres than in underinflated tires. As far as retreading is concerned, a reduction in oxygen diffusion also means less oxidative aging. This is good news in terms of carcass value.

With intelligent tire sensorics Continental will, in the near future, additionally be providing a possibility for monitoring inflation pressure online. This will further contribute to reducing a fleet's fuel consumption.

But it’s not only the buyer’s pocketbook that benefits when all four factors are optimized. The environment stands to profit as well. Internal calculations at Continental AG show that, conservatively estimated, CO₂ emissions can be cut by 318,000 tonnes a year thanks to the 5% reduction in rolling resistance possible with all the regional- and long-distance transport tires Continental has sold in Europe. And there is also a reduction in fine particulate emissions.

This is itself enough to motivate Continental AG's engineers in their continued search for further optimization possibilities.

Author:
Dipl.-Ing. H.-B. Korte
Vice President Product Development & Industrialization – Truck Tyres