1. Field of the Invention
Tires in use wear in a host of ways. One negative manner in which tires, especially truck tires, may wear is in an irregular fashion. When this phenomenon happens, the tread of the tire may become unusable, forcing the user to replace the tire, which is undesirable. This patent application poses a new and useful way of preventing irregular wear, increasing the useful life of the tire tread.
2. Description of the Related Art
Many nominally ribbed tires, such as truck steer and trailer tires for example are subject to irregular wear, which is often characterized by local depressions. Irregular wear is a frequent cause for tires to be removed from service. Accordingly, several design features have been used in the prior art to help prevent irregular wear including microsiping in the outside or shoulder areas of the ribs, providing sipes that are directionally oriented and providing for sacrificial shoulder ribs.
Yet another example of a technique used to prevent irregular wear is shown by U.S. Pat. No. 4,986,325. It discloses the use of angled grooves and sipes that are strategically positioned and sized for improving wet traction. However, this patent also suggests that placing sipes outside the center region of the tread, whith constitutes the middle 80% of the width of the tread, is disadvantageous because such placement increases the risk of heel and toe wear developing in the outer 20% of the tread found on either side of the center region of the tread, which corresponds to the shoulder regions of the tread. In particular, it recommends that sipes should not even extend partially into the shoulder regions of a tread for fear of increasing the risk of heel and toe wear (see col. 6, lines 54-59 of the '325 patent).
Another method for preventing abnormal wear is disclosed by U.S. Pat. No. 5,316,062. It suggests using sipes having different depths in the tread of tire. Specifically, it teaches decreasing the depth of the sipes such that sipes nearer the center of the tire are deeper than sipes found nearer the shoulders of the tire (see FIGS. 2 and 3 of the '062 patent).
All of these solutions found in the prior art address the need to slow down the development of irregular wear when the tire is first put into service but do little to prevent the development of irregular wear as the tire tread wears past these features. Also, they do not prevent traction losses over the life of the tire tread that occurs especially as sipes are worn away.
Accordingly, there still exists a need to prevent irregular wear as a tire tread is worn in a manner that does not lead to a compromise in traction, both at the beginning and throughout the life of the tire.