Does Form Still Follow Function, or Tyre Testers?

During the course of Continental’s annual pre-Christmas event, which has now taken place for more than 10 years, the German manufacturer asked international tyre specialists from several reputed magazines to ponder the following question: “Do driver assist systems require new winter tyre testing procedures?” To summarise the stimulated discussions that took place in Ivalo, Finland, it seems development engineers at Hanover are obliged to try and serve the two masters at the same time.

On the one hand, all tyre manufacturers are interested in achieving good test results for their products. On the other hand, tyre features have to be optimised according to road realities. And this is exactly where Continental has detected a discrepancy: because of the introduction of new driver assist systems some test set-ups seem to be out-of-date and could therefore generate misleading results.

Driver assist systems like ABS, ESC and TCS are now common standard fitments, even on compact cars. They provide increased safety and intervene to correct driving errors. During tyre testing, however, ESC and TCS are switched off in order to test the tyres without the effects of those systems. But such test methods have now reached their limits – particularly when you consider that ESC cannot be switched off in some vehicles without interfering with the electronics. Transferability of the test results therefore also debatable because – depending on the vehicle manufacturer’s philosophy – driver assist systems have different performance parameters and so respond in different ways to different tyres grip characteristics. According to Dr Burkhard Wies from Continental, driver assist systems should also be switched on during tyre testing in the future. This would keep tyre tests in line with latest technological advances for both tyres and vehicles.

Recent years have seen a significant increase in the number of cars equipped with systems like ABS, ESC and TCS. After being launched in 1978, it took about 20 years for ABS to be represented in 40 per cent of all new cars. The ESC stability system, introduced in 1995, has now also reached a 40 per cent share of all newly registered cars – from the top category right down to the compact size. So, equipping cars with electronic management systems has accelerated quite substantially.

Is it still realistic to conduct tests without ESC? Usually these systems are deactivated for the sake of comparability of test results. But, testing tyres without these systems may no longer be state-of-the-art, says Dr Burkhard Wies, head of passenger car winter and replacement tyres development at Continental in Germany: “Without ESC and TCS the transferability of tyre test results to modern vehicles cannot be guaranteed owing to the fact that driver assist systems respond differently,” he states. “Braking with ABS has been part of the standard test programme since 1990. So it’s now time to consider incorporating the other driver assist systems into tyre evaluation procedures as well.” After all, in some cars neither the ABS nor the ESC system can be switched off anyway.

His proposal is supported by methods normally employed by some vehicle manufacturers when conducting tyre approval tests with the driver assist systems switched on: “There is also a huge difference in the results of winter tyre tests performed on vehicles with and without traction control systems,” he explains. “In fact the results were reversed depending on whether or not traction control was engaged.” Tyres for vehicles equipped with ESC should really be adapted to the vehicle electronics in future – and could indeed be quite different to tyres for vehicles lacking driver assist systems.

“Tyre and vehicle testers should react to these new developments by adapting their tests accordingly,” advises Dr Wies. “And the first step in this direction would be to include ESC in future tyre testing procedures.”

There are a high number of options available to test engineers when testing tyres with the ESC activated: different conditions of road, curve radii and propulsion concepts should all be taken into account, advises Dr Burkhard Wies. “Our engineers can meanwhile draw on a tremendous amount of tyre testing experience, and yet we shall still discuss together with test experts from professional motor magazines new methods of testing with ESC in order to obtain objective results.”

An Outlook Into The Future:

Developments to improve driving safety and avoid injury to persons are automatically leading to greater networking of safety-related automobile electronics. Chassis and tyres are delivering more and more safety reserves, measuring systems are able to detect the condition of the road and warn the driver of insufficient distance to the car in front, stability control systems and passive safety devices are being linked up to one another. In a hazardous situation, pressure within the brake system is already increased prior to brake actuation, seat belts are tensioned and the airbags made ready for release.

With today’s safety systems, however, development has not yet reached its peak according to Dr Wies, head of passenger car winter and replacement tyres development at Continental in Germany. The OFE (Online Friction Estimation) prototype car from Continental Automotive Systems, for example, measures the road temperature, the rain or snowfall, the steering angle and the individual wheel speed. The car’s electronics then “estimate” the expected amount of slip and warn the driver that the road is dangerously slippery. In combination with an advanced navigation system, the car first alerts the driver on the basis of detected road conditions that he is driving too fast into a bend, and, in a second step, tells him to activate the brakes. If the driver fails to respond, the system can in future actively intervene and reduce the speed to ensure safe cornering.

“Thanks to the smart networking of sensors and vehicle control systems this prototype helps give a dramatic improvement to safety, particularly on slippery roads,” says Norbert Kendziorra, project manager for the development of the OFE prototype at Continental.