AKRON (April 16, 2002)—It's April again, spring is in the air, the forsythia is blooming and retreading is on the minds of tire people everywhere.
This year is a little strange without the annual International Tire & Rubber Association's convention/trade show. But there are other things that are bringing retreading to the forefront of our attention, such as the scrutiny we are now getting in Washington. This has many people looking at the causes of tire and retread failures.
As we all know, the most critical factor in retreading is the casing itself. If a tire has been neglected and poorly maintained, when retreaded it is doomed to failure—not because of the process of retreading but because the foundation it provided for the new tread was weak and unstable. Tire inflation maintenance both before and after the tire is retreaded is critical to the success of any retread.
Air 'em up
The Technology & Maintenance Council (TMC), through its Tire Debris Prevention Task Force, conducted studies in 1995 and again in 1998 on tire road debris that have confirmed that poor retread manufacturing processes are not the primary cause of “alligators” littering the highways throughout our country. In fact only 8 percent of the tire debris could be attributed to this cause. Rather, the great majority (88 percent) of failures was caused by underinflation that existed either as a long-term condition or was induced by road hazards.
The next question that begs to be answered is: “What is the state of tire inflation on commercial vehicles in this country?”
At the TMC Annual Meeting last month, the Tire Debris Prevention Task Force presented the findings from its Tire Air Pressure Study that it conducted in the second half of last year. The task force was interested in studying real world tire pressures on a wide range of vehicles and types that operate on U.S. highways.
To collect this data, the task force used statistics that tire companies routinely collect while conducting fleet surveys for their customers. Trained, skilled field service engineers who have the proper tools and accurate gauges to do this work conducted these fleet surveys. They were performed on Saturdays or in the early morning before vehicles had run on the road and while the tires were still cold in order to ensure tire pressures were accurate.
Although fleet survey and tire pressure data were available on fleets from tire company archives, no such data were available on owner operators. Therefore, this data had to be collected at locations in which these drivers would be stopped for at least three hours in order for their tires to cool down to ambient temperature such as “trucker appreciation events.”
Two large events were selected: The Walcott Truckers Jamboree and the Reno Truckerfest 2001 held last summer. Task force volunteers conducted tire pressure checks on owner-operator vehicles at these two locations.
The tire pressure data collected on owner-operator tires as well as from fleet surveys were entered into a database. Each fleet was identified by a coded designation for fleet name. No actual names of fleets were entered into this database.
Fleet type, fleet size, operation, tire size, targeted air pressure for steer, drive and trailer tires, and gauged pressures were entered as well. No data regarding tire make, model, retread number (new or number of retreads), tread depth, tire condition or other comments were included in this database since this information had no bearing on the purpose of this study, which focused on the state of truck tire air pressures.
Included in the database were 35,128 tires on a total of 4,786 trucks and tractors, 1,301 trailers and 1,500 motor coaches operated in 174 fleets.
Working the numbers
In analyzing the data, the Tire Debris Prevention Task Force selected several parameters to use to judge the level of underinflation. Tires that had inflation pressures that were 20 psi or more under their target pressure indicated a tire inflation maintenance problem. Tires that were underinflated 50 psi or more were considered “flat” and presented a probable tire debris problem in the making.
Since tire pressure should optimally be maintained with +/- 5 psi of the target pressure; this parameter was established as being a measure of inflation maintenance.
The findings were quite interesting. Here are a few of the highlights:
1. Only 43.6 percent of all tires in the survey were inflated within +/- 5 psi of their targeted air pressure.
2. 21.6 percent of all vehicles surveyed had at least one tire underinflated by 20 psi or more (as compared with their targeted pressures).
3. 4.3 percent of all vehicles surveyed had at least one flat tire (50 psi below the targeted pressure).
4. 21.7 percent of all dual tires had mismatched air pressures with the difference being greater than 5 psi.
5. There was not a great difference between the tire pressure on the right and left sides of the vehicle (less than 1 percent better on the left side).
6. There was not a great difference between the air pressure in inner and outer dual tires (less than 1 percent better inflation in outer tires).
7. Overinflation was a problem with 13.1 percent of all tractor tires overinflated by 6 or more psi and 16.5 percent of all trailer tires with this condition.
8. 46 percent of all tractor tires were within +/- 5 psi of their targeted pressures, while only 37.8 percent of trailer tires fell into this category.
9. The incidence of flat tires (50 psi under the targeted pressure) was essentially the same on tractors and trailers with 0.84 percent of all tractor tires being flat and 0.85 percent of all trailer tires being flat.
What the stats mean
A zillion more pieces of data can be culled from this 71-page report. But it would take more space than I am allotted to present it all to you now.
However, what is extremely interesting from a retreader's point of view is that while the percentage of trailer tires that were found to be flat was essentially the same as tractor tires, and trailer tire maintenance was only somewhat worse than tractor tires, the surveys of tire road debris found that more than 70 percent of the tires analyzed had rib type tread patterns—indicating that these tires came off trailers and dollies.
Why is this? The answer goes back to tire inflation maintenance.
As a general casing management practice, almost every fleet in the country places its second and third retreads on trailing axles. These tires have the cumulative, weakening effects of underinflation in their casings. This means that they have perhaps several more years of operating underinflated than their new or once-retreaded counterparts on tractors.
Since only 0.85 percent of all trailer tires are flat—50 percent below the targeted inflation pressure would indicate a puncture or other air retention problem—the majority that fail due so because of casing fatigue from long-term underinflation.
With closer government scrutiny of the retreading industry—as fallout from the TREAD Act—what should be done?
As has already been reported, the National Highway Traffic Safety Administration is testing retreaded tires to see how they perform compared with new tires. They want to see how commercial retreads compete against the current FMVSS 119 standard, which is the same test new truck tires must pass. I am confident this will not be a problem.
Will there eventually be a standard test that truck tire retreads must pass? Probably. You only have to look at the passenger tire area to see that NHTSA will most likely take the lead from this segment and establish a standard test for retread performance as it did years ago for passenger retreads. Is this bad? No, not necessarily.
I cannot imagine that the government would require every retreader to have his/her retreads tested. This would be extremely burdensome on the retread industry, especially small retreaders.
Rather, the retread process that is used would have to be tested. This process could be the Industry Recommended Practices for Tire Retreading or the various processes used by retread companies and their franchisees that is documented in their process manuals. As long as each individual dealer follows the process, they would be certifying that the retread could pass the test.
Retreading in danger?
Don't fret that retreading is in danger of being exterminated. There are far too many users such as school bus, truck and government fleets (which have been mandated to use retreads) to name a few that would be seriously, financially impacted if retreading was restricted. Politically, this would be an unwise avenue for a regulatory agency to take and one that would be blocked by the trucking and tire industries.
But knowing that long-term fatigue resulting from underinflation is undermining your retreads, you should start immediately to take a closer look at the casings you accept for retreading.
First off, make sure that the casing is designed for the service to which it will go. Often, the inspector can rely on the tread pattern of the original tire to determine the application for which the tire was originally de-signed, but if the tire was retreaded it may be necessary to examine the sidewall markings. Some tires will say “Not for Highway Use,” “Farm Use Only,” or specify the axle for which they were designed.
Some tires have maximum speed ratings. A casing with a maximum speed of 55 mph should not be retreaded for an over-the-road operation that you know runs in excess of 65 mph. It's important that your inspector have an idea of which application each inspected casing will be required to operate in, as well as the expertise to make the proper judgment about which casings are acceptable.
Tires that are several years old, have been retreaded before or exhibit damage of any kind should be closely scrutinized to determine whether their air retention integrity has been compromised and whether their air pressures have been properly maintained. Sidewalls should be closely inspected for tell-tale signs of fatigue that can result in zipper ruptures. And innerliners must always be closely in-spected to check for any signs of running underinflated.
Almost every retreader now has some form of non-destructive inspection equipment. These machines should be used as an aid to the inspector, not as the main decision maker regarding casing acceptability. Nothing can take the place of a good inspector's eyes and ears, and the sense of touch in his/her fingertips to detect problems.
Truck tire retreading is going to be around for a long time. It's our job, though, to make sure each retread is of the highest quality and that each casing is sound and able to make it for the long haul.
For a copy of the TMC Tire Air Pressure Study, contact Robert Braswell at the Technology and Maintenance Council, (703) 838-1776.