A common complaint from many performance tire owners relates to noise. More specifically, the increase in noise over the life of the tires as they wear. The traditional directional tread patterns do have a propensity to get louder as they wear. This can really become an issue if uneven wear is introduced into the equation. Since directional tires can only be rotated front-to-rear, getting even wear can become problematic. In the case of staggered set-ups, even wear can only be achieved in the dreams of tire engineers.
Sumitomo HTR Z II
Michelin Pilot Super Sport
The driving force behind the asymmetric pattern being explored seriously was due to Europe having phased in new stricter noise standards over the past few years. If interested, you can find out about this mandate by reading "United Nations Economic Commission for Europe (U.N.E.C.E.)."
The directional tire design, with its V-shaped pattern to pump water out of the way, was presenting challenges in meeting these new standards. A solution was found with the asymmetric design. An asymmetric tread pattern blends the different traction elements with different patterns across the face of the tread. The outboard side consists of larger tread blocks or ribs for dry road cornering capability and increased contact patch, while the inner half tends to feature small independent tread blocks for wet conditions for summer tires and wet and snowy conditions in the case of all-seasons.
An attractive added benefit to the asymmetric design is the ability for multiple tire rotation patterns instead of the restrictive front-to-back with directional tires. On a staggered car, you can go side-to-side to try and help with uneven wear issues that are very common on those set-ups. In summary, the asymmetric pattern is meeting and exceeding the traction levels of the directional patterns, while also hitting the lower noise targets, and allowing better rotation schemes.
To learn more on how to properly rotate your tires, read "Tire Rotation Instructions."