I have been involved with the technical, marketing and litigation aspects of the tire industry for more than 50 years and, like most of us, have a strong interest in realistically addressing tire safety opportunities.
About 12 years ago, I petitioned the National Highway Traffic Safety Administration (NHTSA) to increase the height of the wear-out indicators on tires to a deeper tread remaining configuration from the prevailing 2/32-inch mark. In many tire disablement situations, I saw that when a radial tire was down to the ``legally defined'' 2/32 minimum in two adjacent main grooves, it exhibited marginal wet traction, localized shoulder fast wear/exposed steel and declining resistance to certain service misuses.
At that time I had no strong scientific evidence to support this request, and on that basis I respectfully understood and accepted NHTSA's reasons for rejecting my petition.
However, hard data now exist to restate the need for a revised tire wear-out standard. The mandated 2/32 criterion does not apply to today's tire and vehicle configurations and can be seen as contributing to certain tire misuse disablements as well as driver-related hazardous control situations.
Interestingly, even the marginal 2/32-inch tread depth guideline for removal of a tire from service is not recognized by all states. Six have chosen to weaken or ignore it. California has a 1/32-inch rule while New Mexico, North Dakota, West Virginia, Montana and South Carolina have no rule.
The Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act should be strengthened to give NHTSA, rather than individual states, the proper authority to mandate a uniform federal tire wear-out standard.
At the 2006 International Tire Exhibition and Conference (ITEC) meeting in Akron, a peer review group of experienced tire industry technical experts was not able to identify satisfactorily an adequate scientific basis for the original 2/32 requirement in radial passenger tires. At that time, research work done in 1967 on bias aircraft tires was ``extrapolated'' to address hydroplaning concerns in passenger tires. A 1975 Department of Transportation (DOT) report (HS 801 438) recommended ``that tires should be replaced when they reach a groove depth of 2/32 of an inch.''
Dr. William Blyth, a retired mechanical engineer from Palo Alto, Calif., who taught applied mechanics at San Jose State University for 42 years, presented a paper at the 2006 ITEC conference on the minimum legal tread depth standard and the importance of tread depth and tire placement for wet traction. In it he showed evidence that tires can lose an important portion of the wet traction capability originally designed into them when they are worn beyond the 4/32 tread level.
Peer review of Dr. Blyth's paper-and much conversation-amplified the consensus that the wet traction data justified adding 2/32 more tread depth to the current 2/32 standard.
When Dr. Blyth's paper was published in Rubber & Plastics News, a sister publication of Tire Business, no objections to his premise were received from the paper's approximately 16,000 rubber industry readers worldwide.
Besides the demonstrated need to increase the tread depth indicator requirement for wet traction, an upgraded wear-out standard will impact another industry topic of ``old'' tires and facilitate their earlier removal after being weakened by service oxidization (not chronological age), environmental conditions and service abuse.
A recent unscientific Tire Business Web site poll found that 75 percent of dealers favored a 4/32 removal standard. Dealer anecdotal experience cannot be discounted since they are immersed every day in the real world of tire service anomalies.
Even though safety is its primary mission, NHTSA initially expressed environmental concerns in its response to my June 13, 1995, proposal regarding the earlier disposal of worn tires. However, the RMA recently reported industry progress in the more efficient and effective recycling of scrap tires.
In summary, I suggest that:
* The TREAD Act should give NHTSA the authority to mandate a uniform federal tire wear-out standard (thus removing it from the discretion of states).
* The tread depth legal wear-out indicator dimension should be upgraded from the current 2/32 standard to 4/32. This upgrade can be grandfathered in so as to not impact current tire mold configurations or performance claims.
* ``Out of service'' should be defined as when any single tread depth indicator becomes level with the wearing surface at any location anywhere on a tire's crown or shoulder.
* Tire manufacturers be given indicator placement flexibility to optimally address wear characteristics of a particular tire's design.
Hopefully this overdue tread-depth out-of-service safety upgrade proposal will, no pun intended, finally get traction.
Harold Herzlich is president of Las Vegas-based Herzlich Consulting Inc. and is technical editor of Rubber & Plastics News.