At the National Tire Research Center in Alton, Virginia, USA, research is being conducted into the replication of EU noise and wet grip tests on an indoor rig
Of the three tests specified by EU tire labeling legislation, only rolling resistance is currently conducted indoors on a test rig. Industry experts believe that in the long term, the wet grip and tire noise tests could also be brought off the proving ground and onto the rig, and research is now underway to this effect.
One such project is at the National Tire Research Center (NTRC) in Alton, Virginia, where a team led by technical director Kevin Kefauver has conducted wet grip and noise tests on the facility’s MTS LTRe Flat-Trac machine.
For wet grip, the team took advantage of the LTRe’s large controlled braking capacity and wet-test capability. “We wanted to see how well we could predict the label value,” explains Kefauver. “We took five different European tires that were already labeled, ran the EU test procedure on the machine and compared them to the label values.”
The tests were conducted on the machine’s regular 120-grit test surface. “We found that we predicted a lower grip level than on the label, but we know that the surface we were using had less texture depth than the EU test standard,” Kefauver explains. “With that in mind, one of the things we’re working on in the first half of this year is being able to apply a more porous surface to the belt.”
Unlike in the wet grip scenario, the outdoor label test for noise could not be replicated on the rig because it is a pass-by measurement. “Instead, we measured the sound at the contact patch,” Kefauver explains. “We installed a small acoustic chamber around the test tire and used an industry-standard sound-intensity probe to take the sound measurements.”
Again, labeled tires were measured on the machine and the results rank-ordered for comparison with the official label values. As was the case with the wet-grip results, the rank order was similar to the official label values.
“The delta between the loudest and quietest on the label values was also very similar to what we’d measured on the machine,” he notes. “Given our results, people can already come and take advantage of the measurements we can make. If people are working on radiated tire noise, lab testing can be done earlier in the cycle than might normally be the case, and can help guide the development direction. It can certainly rank order their tires, and help predict what the final label value might be.”
For both testing scenarios, repeatability between tires of the same construction were very good, but more development work will be required. For noise testing, that means further investigating the relationship between the indoor test at NTRC and the outdoor label test. For wet grip, it’s all about the surface.
“To get a deeper surface, we can use the technology we developed for our cleat testing to create one long, non-uniform surface that we apply to the belt,” says Kefauver. The material is likely to be a very high-durometer rubber, although he acknowledges that the tricky possibility of putting asphalt onto the belt and thereby providing an even closer relationship to an outdoor surface “is something we think a lot about”.
For Kefauver and his colleagues, more research beckons…
May 6, 2015
