Tyre testing: Evolving and expanding
By Ron Kennedy*:
Tyre testing has expanded considerably due to increased government regulations and labelling requirements, requests from vehicle OE manufacturers for test data to assess tyre performance, as well as specialised tests developed by the tyre companies themselves
Much has changed in the area of tyre testing over the years. Walking into the indoor test department of a USA tyre company in the 1970’s you would have seen rows of test cells containing road wheels running tyre endurance and high speed tests to assess performance to meet government regulation FMVSS 109 or internal company QA standards. A separate room was typically allocated for tyre static tests such as tyre dimensions, plunger energy, bead unseating, vertical spring rate, and ink footprints. Any other “specialised” testing such as modal vibration, noise, high speed uniformity, or tyre-road contact interface measurement was located in research or advanced engineering departments.
Tyre testing has expanded considerably since then due to increased government regulations and labelling requirements, requests from vehicle OE manufacturers for test data to assess tyre performance, as well as specialised tests developed by the tyre companies themselves to investigate their tyres’ performance or to provide input for their tyre and tyre-vehicle simulation tools.
The energy crises during the 1970’s led to the introduction of US government vehicle fuel economy regulations. Although set as a vehicle fleet requirement, this trickled down to the tyre manufacturers in the form of a rolling resistance specification from the vehicle manufacturers for tyre approvals. A SAE committee developed the J1269 test standard in 1979 to establish a common test procedure for this testing. Rolling resistance measurement became a routine test performed during the tyre development process. To provide more meaningful results, the SAE J2452 and ISO 28580 standards were later developed to measure rolling resistance at expanded test conditions and introduce additional data handling techniques.
As the 1970’s came to a close the US government also implemented Uniform Tire Quality Grading (UTQG) tests and tyre labeling for tread wear, wet traction, and temperature in order for tyres to be sold in the marketplace. The wear and traction tests are still performed today at a specified outdoor test facility using the government prescribed test procedures while testing for temperature resistance is performed on an indoor drum at increasing speed. Tyre labeling requirements have been introduced in Europe and other countries during the past 10 years, and typically require ratings for fuel economy, wet traction, and possibly pass-by noise. These tests are carried out by the tyre companies using government specified surfaces and test procedures.
Vehicle OE manufacturers have added additional testing requirements to the tyre approval process in new vehicle programs as vehicle performance requirements have evolved and new test capabilities have been developed. An example of this is the testing of accident avoidance handling maneuvers, which gained importance in the late 1980’s as SUV’s became popular in the vehicle lineups. To provide input to their accompanying vehicle dynamics simulations the vehicle manufacturers required the tyre manufacturers to supply tyre force & moment test results at high slip angles, loads and camber angles for tyres under consideration. Flat belt force and moment test machines became commonplace in the indoor test labs in the industry.
Tyre tread wear testing requirements have also been added by vehicle OE manufacturers. The test procedures are unique to each vehicle company, differing in routes, lengths, and measurement techniques. Machine capability and test procedures have been developed to measure tread wear on indoor drum test machines that provide tyre development engineers a quicker assessment of their designs, and in some cases are accepted by vehicle manufacturers in place of outdoor test results.
Work is continuing on the development of other indoor test capabilities to more closely replicate the outdoor test conditions, such as tyre traction on various surfaces and conditions, whether dry, wet, ice, or snow. Some indoor facilities have been expanded to allow vehicles to be driven over these surfaces to evaluate traction and handling performance in order to extend the testing season.
On-vehicle noise, vibration and harshness (NVH) and handling performance testing is also a routine part of tyre approval testing carried out by vehicle OE manufacturers. This has historically been done via trained driver-evaluators subjectively assessing the tyre performance. Measurement capabilities and test procedures have been evolving during the past several years to augment the subjective assessment with objective measurements made using accelerometers, microphones, and GPS units to track the vehicle path and measure vibration, noise, and accelerations. Metrics are being established to relate the objective measurements to the subjective assessments so they have meaning to the comfort and feel of the vehicle occupants.
Specialised testing capabilities continue to be developed by the tyre companies to probe tyre performance under various loading conditions. The tyre-road contact interface is of primary importance and thus several methods have been developed to provide parameters of the contact area such as localized pressure and slip displacements. If proven successful in characterizing tyre performance, these specialized tests then become part of the routine tyre development process.
Although trumpeted as an alternative to tyre testing, the use of tyre and tyre/vehicle simulations in the tyre development process has actually led to additional types of testing to provide inputs to the models. For example, semi-physical tyre models, such as FTire and Swift, need the measurement of various tyre values such as springrate on different surface contours and modal responses to provide input parameters.
Much has changed in the testing of tyres over the years. It is expected that tyre testing will continue to evolve and expand in the future as improved machine and measurement capabilities are developed, allowing better probing and assessment of tyre performance.
* Dr. Ron Kennedy is Managing Director of CenTiRe, leading tyre research centre