Joe Godina, a fleet manager with Heavy Weight Transport, inspects air pressure. (Yokohama photo)
ATLANTA, Ga. — Running an accurate tire test isn’t a matter of simply throwing on new rubber and tracking fuel receipts. A true test requires at least 30 wheel positions to remain at the end of the test, and the use of a control fleet.
Peggy Fisher, president of Tire Stamp, shared some best practices for running tire tests at this year’s spring meetings of the Technology & Maintenance Council.
“In the real world, conducting tire tests is a challenge and can be a real pain in the butt,” she acknowledged. “It’s hard. There are so many variables you have to be concerned about.”
Just a few of these include: vehicle model; routes, weather; loads; and drivers.
“All these things can affect test results, and stuff happens,” Fisher said. “Tires get damaged. They’re repaired. They just magically disappear. And when you ask the driver or technician what happened to the tire on his truck, you get ‘I dunno.’”
Fisher said to get a 90% confidence factor in the test results, at least 30 tires must remain at the end of the test. She advised starting with more than that, as some will be lost due to damage.
“You’re probably going to lose 10-15% of them and they’ll fall out of the test,” she said. “You can use smaller sample sizes but the results won’t be as accurate.”
She also suggested using broken-in vehicles with 15,000-30,000 miles on the odometer. The trucks used in a test should be identically spec’d and loads should be about the same. Drivers chosen for the test should be free of unusual driving habits and represent the average driver within the fleet – don’t include the best or worst drivers. Trucks should be aligned before the test begins – even if they’re new.
Retreads that are tested should have the same casing, manufactured by the same supplier, and be within one year’s manufacture of each other. All test tires should be identified and technicians and drivers notified about the test, so that the tires are retained if they fail on the road.
“Make sure the tires themselves are identified and I also highly recommend stenciling the wheels with ‘TEST’ so people don’t miss it. Label the vehicles so that technicians and drivers are alerted to the fact there are test tires on that vehicle,” Fisher advised.
Rim sizes must also be matched, as do the wheels. Test tires should all be installed within 30 days of each other to minimize the impact of weather. Tire pressures should be checked at least monthly, and alignment should be checked several times over the course of the test, Fisher said. Tread depths should be measured and recorded at regular intervals.
“Take them consistently at the same spot in a major tread groove,” Fisher advised. “Use the valve stem as a reference point and take it consistently at the same spot.”
An initial analysis can be conducted when the tires are 50% worn.
Randy Patterson, senior field engineer with Bridgestone, said communication throughout the fleet – and outside it – is crucial to running an effective test. Some of the people who need to be involved in the discussions include: the parts manager; maintenance manager; shop supervisor; technicians who will be touching the tire; drivers; and even dispatchers. Outside the fleet, the dealer service personnel, tire manufacturer representative, and truck sales manager should all be looped in.
Some of the biggest mistakes Patterson has seen fleets make when running tire tests are: failing to track the test tires; failing to track the tires once they’re removed from the vehicle; not using a control group; not doing enough inflation pressure checks during the test; using mismatched vehicles; and pulling the tires too soon.
“Product evaluations are hard,” he acknowledged. “They take a lot of time to do, a lot of effort. The more effort you put in up-front and the more communication you have, the better off you are. If you collect bad data, you’re going to have bad data as a result.”
Lee Long, director of fleet services with Southeastern Freight Lines, has 95,000 tires on the road on any given day.
“Everything we do is driven by data,” he said. He urged fleets to work with their tire supplier to use their facilities for testing. He took two trucks to a tire company test track to conduct coast-down testing. Long also noted calibrated tire gauges should be used to measure inflation pressures.