Recently I met some highway engineers from Nordic countries, who have the problem of tire traction under their severe winter conditions. The continuing use of studded truck tires is causing concern about road wear and requires changes in the design specification.
While the use of studded tires has its supporters and opponents, it was the subject of truck tire-to-road noise that was the subject of the meeting. The question arose as to whether the changes in surface texture design required to resist studded tire damage would yield higher noise levels. Would the noise ratings now part of the tire labeling scheme be related to the actual noise levels on these surfaces?
A comprehensive testing program has been conducted, involving detailed measurements of various road surface properties and textural characteristics. The surfaces included the latest ISO 10844 (2014) specification. The noise measurements for a range of truck steer, drive, trailer and retreaded tires are likely to be presented at the 2016 Tire Technology Conference. As with road surface data, a great deal of tire property and scanning data has been accumulated.
The time and expense of such a study is considerable, as is tire testing for the legal requirements of tire noise. The process for creating these measurements allows some rather strange practices, such as a ±1.5dB allowance for variations in the ISO 10844 test surface and the reduction to ±1.2dB with an MPD of ≥0.4mm. There is also a correction of -1dB for the limiting accuracy of the measurement system and the rounding down to the lowest integer. Additionally any infringement regarding the noise value stated is down to each state in the EU. These circumstances are a basis for confusion and offer little in the way of reassuring the customer as to the reliability of the data.
I recall the early days of tire modeling, when tire designers were hesitant about even the basic data, such as load/deflection data. Today tire modeling is the basic tool of tire designers and is rapidly increasing the accuracy and range of tire properties now available. We can even see the start of a holistic approach, embracing materials behavior down to the sub-nanoparticle level.
More specifically, tire noise generation mechanisms relative to dimensions, structural design, tread pattern design and some aspects of the material properties of tires when rolling on a smooth surface can now be accurately modeled. Over the past decade the introduction of idealized road textures and some forms of real road surface textural features can be added to these models.
So we come to the obvious question. Where are the highway engineers with regard to the modeling of road surface textures and their practical introduction into road surface design – not only for noise minimization but for wet grip, comfort and reduced tire energy losses?
It is certainly true that road surfaces change during service use and are also sensitive to climatic conditions. But the same is true for tires. The highway engineer now has laser-based equipment that can create a three-dimensional display of road textures capable of being described mathematically. I suspect that our highway engineering friends are extremely good hands-on engineers who just may be a little shy in embracing the mathematical approach.
In the early 1990s Dunlop showed that it was practical to create replica road surfaces with very similar polishing characteristics and thermal properties to those of real road surfaces. These surface replicas were able to be attached to drums for noise and other measurements and were adopted by a number of tire companies. Noise measurements on curved surfaces are not perfect but the discrepancies relative to the road situation are resolvable.
Today we have the technology of 3D printers and it would seem feasible to replicate the ‘specified’ road texture at will from a range of materials. Given these three approaches, surely it is time that the tire and road engineers got together and agreed the ideal textures for roads that would be widely adopted to offer the tire engineer a chance to optimize tire properties, one of the first and most urgently required being t he minimization of tire-to-road noise generation.