Studies of heavy truck tire debris and nitrogen inflation of tires may end up refuting common wisdom on both subjects, according to speakers at the Annual Clemson University Scrap Tire Conference.
The University of Michigan Transportation Research Institute recently completed submitting data to the National Highway Traffic Safety Administration on a heavy truck tire debris study NHTSA commissioned from the UMTRI. Final results should be available in June or July, according to Oliver Page, a research fellow at the UMTRI's Transportation Safety Analysis Division.
Page-who spoke at the conference last month at Hilton Head-said the objectives of the study are to investigate the underlying causes of heavy truck tire failures, determine the extent of truck tire failures for retreads and determine the crash safety problems associated with heavy truck tire failures.
``The public automatically assumes that tire debris is from a truck or trailer, and is a retread,'' Page said. The goal of the study, he added, is to test the truth or untruth of that assumption.
As planned by NHTSA and the UMTRI, Page said, the heavy truck tire debris study consisted of five tasks: a review of the literature on tire debris, analysis of crash data, data and debris collection, data/failure analysis of the debris, and a final report and briefing.
Tires were the No. 2 defect found in trucks involved in fatal crashes between 1995 and 2004, second only to defective brakes, the study found during the crash data analysis phase. However, defective tires were found in only 445 of the 50,962 fatal truck crashes during that period, it said.
``Trucks represent 8 percent of fatal crashes, but only 3.3 percent of the vehicles on the road,'' Page said.
Analyzing crash data varies in difficulty from state to state, according to Page. Some states provide a complete police narrative as to the cause of an accident, whereas others are considerably less forthcoming, he said.
UMTRI investigators examined 1,194 pieces of debris and 300 casings gathered in California, Arizona, Indiana, Virginia and Florida, Page said. Casings had to be rimless and obviously from large trucks, and debris had to be at least two feet long and four inches wide, he said.
Deliberately dumped casings and debris were not used. ``Highway crews are expert in telling the difference between debris from blown tires and debris from dumped tires,'' Page said.
Debris was presorted to eliminate passenger and light truck tire samples, according to Page. ``Just because it was a large piece didn't mean it was from a truck,'' he said.
Tires were analyzed via tests and physical assessments, including visual/tactile examinations, trade depth gauging, tape measures and a jeweler's device, according to Page. A database was constructed from the examinations, classifying the samples according to tire size and manufacturer, original tread or retread, and evident causes of failure including manufacturing/process issues, overdeflected operation, road hazard, maintenance/operational issues and indeterminate causes, he said.
Because the failure analysis is ongoing, releasing the early results may not give a correct picture of the final outcome, according to Page. Liberty Tire of Minerva, Ohio, is responsible for shredding the casings and debris at study's end into crumb rubber and playground fill, he said.
Meanwhile, a study of oxygen and nitrogen permeation through tires showed that nitrogen may not be the tire-inflation panacea it's been touted as being, according to Donald D. Amos, manager of industrial standards and government regulations for Continental Tire North America Inc.
``I do not oppose nitrogen inflation in tires, but I want to see the claims made for it based on sound science,'' Amos said. ``I won't go out of my way for it, and I won't pay a lot for it.''
According to Amos, oxygen permeates out of or into a tire depending on the oxygen partial pressure differential between the atmosphere and the tire cavity. Permeation models demonstrate that high-purity nitrogen inflation has 35-percent less inflation loss in tires compared with air, he said.
``Oxygen will get out of a tire faster than nitrogen,'' Amos said. ``You can take that to the bank.''
However, nitrogen's lower permeation rate has no influence on inflation loss from bead and rim seal leaks, valve leaks, rim leaks or punctures, he said.