How Continental's tire test program makes subjective an objective13 December 2011
Continental tests 120,000 tires a year globally; the company's Scott Armstrong reveals technology and techniques.
Continental tire tester Scott Armstrong is—professionally speaking—a clone. If two of the German company’s testers check out the same type of tire on the same type and specification of vehicle but not necessarily on the same track or road route or same country, they will come to the same conclusions, even though their views are subjective.
“Continental drivers are trained for two years on how to do subjective evaluations. Like my colleagues, I have a database in my head which allows me to be as objective as possible,” says Armstrong as he whirls a Jaguar XJ shod with 20-in ContiSportContact 3 tires around the MIRA test track in the U.K.
“My job involves testing different tires and driving them in exactly the same way at the same speed through corners so that I can judge the differences in them—and not differences in my driving.”
If it sounds physically and mentally taxing, it is. But, says Armstrong, a member of the Continental Subjective Characteristics (Outdoor) team: “It really does work.” If he completes a shift, is on vacation or unwell, a colleague can continue the subjective test program reports: “And you will not see the join between them as we come to the same conclusions.”
The array of testing tools, equipment, and computer simulation work remains essential to new tire development, but none of that can provide the interface evaluation generated by a human, even though that deeply ingrained database does imbue the company’s tire testers with an almost machine-like capability.
Generally, Continental testers focus on just one or two vehicle brands. Armstrong specializes in Jaguar and Land Rover, which are part of the same Tata-owned company (JLR).
With regard to objective tests of tires, these involve targets set by the OEM including the development of standards to meet NVH, rolling resistance, and braking distance specifications, all of which are physically measurable.
“We can produce tires that meet all these requirements set by JLR, but that is not quite enough,” explains Armstrong. The added—vital—element is also to meet the criteria expected by a JLR buyer; Armstrong and his testing colleagues need, in effect, to become JLR buyers.
To do so, the Continental teams work with OEM specialists such as JLR’s Vehicle Integrity team, headed by Mike Cross. The JLR specialists play a salient, overall role in ensuring that the cars they help develop will handle, ride, and particularly steer to provide the driving experience required by an end user.
Continental’s newest high performance tire, the ContiSportContact 5P, is expected to be used by Jaguar on future models but has not yet been cleared for the XJ. The 5P’s design, with its macro-block configuration on the outer shoulder and solid central ribs, uses Black Chili Technology (BCT). It incorporates a specially developed compound technology using a type of racing grade carbon black for a quick warm-up and enhanced stability.
The polymers—both long and short chain—in the compound are reinforced with nano-particles to provide markedly increased suppleness to enhance grip and stability. Special grip resins are also incorporated to provide what Continental describes as “optimum interlocking” on both wet and dry road surfaces, to shorten braking distances. The 5P also has reduced rolling resistance.
Continental opted not to use a “4” designation to follow the Contact 3, as the number is deemed unlucky in some countries!
Contact 3 continues in production, as a typical manufacturing life of a tire is 10 years.
Armstrong starts work on the development of a tire for a specific model up to three years before the vehicle’s on-sale date. Initially, he tests a reference tire, a prototype that will have been manufactured to the basic objective level required.
“I drive the car fitted with this tire and learn that level; then all new specifications which we may make during development, I can compare directly with the initial reference version.”
Most OEMs use similar tests for their tires although a few, such as Porsche, also require very high speed dynamic tests including passing lane changes at 250 km/h (155 mph).
As Armstrong takes the Jaguar around the demanding MIRA track, he is looking at the rudiments of responses: “Firstly, I consider the steering wheel to ensure there is no phase lag immediately the wheel is moved because the tires may be too flexible, inducing a slight time lag from turning the wheel to the car moving its position when the tire takes up the lateral force from the input as a slip angle is generated—i.e., a vague steering feel.
"Developing a new tire is often a juggling act; change one thing to make an improvement in response, and this may affect comfort. And we do not want steering to be too nervous at high speed—it may need to be slightly desensitized, but then it has to be responsive at low speed. As a tire goes faster so it expands and changes its footprint. Tire design is a highly complex business, and my part in that is to be a performance reporter. Of course, much can be achieved via modeling, but you still have to have a human test driving it extensively to answer the question, ‘Is it good enough?’”
Armstrong does most test driving with another person on board or with 80 kg (176 lb) of ballast.
Rear axle stability is particularly significant. Armstrong states that OEMs always pay particular attention to slalom tests, lane change (elk test) performance, and braking in a turn.
An important aspect of a tire tester’s work in Europe is the difference between winter and summer tire design.
In the U.S., all-season tires are popular (the market predominantly wants comfort and high mileage) whereas in Europe, Continental, which has its headquarters in Frankfurt, regards handling as the priority. In some European countries, including Germany, Austria, parts of Italy, and most of Scandinavia, winter tires are a legal requirement for several months of the year.
Continental regards winter tires as outperforming summer at ambient temperatures of 7°C (44°F) or below. At 5°C (41°F) ambient and a speed of 100 km/h (62 mph), a winter tire fitted to a Volkswagen Golf can reduce stopping distance by 4.8 m (15.7 ft) on a wet surface, states Continental; in snow, the improvement is 8 m (26 ft) from a speed of 48 km/h (30 mph).
Winter tires use a softer compound mix and so deform more easily, keying into road surface irregularities. Harder mixes tend to ride over irregularities, a situation exacerbated by a film of water. The contact patch of any tire has about 14/100ths of a second to do its job.
Used in appropriate conditions, the wear rate of a winter tire is described by Continental as being similar to that of a summer. Minus points include a slight increase in noise at cruising speeds and also a slight increase in fuel consumption.
In snowy conditions, it has been proved that the best material to get a grip on snow is snow—so winter tire grooves allow for compaction, states Continental.
Continental annually tests some 120,000 tires, which represents about half the company’s daily total production. The tests are carried out in every market into which it sells.
Tire pressure monitoring becomes an EU requirement for all new cars in November 2012, and the company regards this as a significant contribution to tire safety.
Ironically, while reducing tire noise has been an aim of all tire manufacturers in recent years, the emergence of EVs is now focusing tire manufacturers’ minds on the possibility of increasing noise as a warning to pedestrians of the approach of a vehicle.
It is likely to have a knock-on effect on other aspects of a tire—something else that Scott Armstrong will need to factor into his mental tire database.
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