On-road or in-lab: Could tire industry move toward indoor tire abrasion testing standards?

GREENVILLE, S.C.—To get where you really want to go, you sometimes have to start somewhere else.

That likely is the case with tire abrasion regulation testing, which looks to be starting its journey on the road before things can be brought in-house.

There's good reason for that, according to Matthew Van Gennip, vehicle dynamics technical specialist with Link Engineering, who explored the issue during a presentation at the recent Clemson University Global Tire Industry Conference in Greenville.

Simply, you have to start somewhere. And when it comes to tire abrasion, there's an urgent need to start.

Because for the industry, tire abrasion data is a key that unlocks a deeper understanding of so many critical issues like performance—ensuring longer-lasting tires amid rigorous new-mobility demands—and especially for environmental stewardship.

With that in mind, the industry is working to establish testing that helps measure and manage abrasion. A number of groups are helping to lay a foundation, and the European Tyre and Rim Technical Organisation is among them. That group, in particular, is leaning on convoy testing. At least, for now.

"I would argue that convoy testing isn't really cost-efficient," Van Gennip said. "It's a lot of work, a lot of time, a lot of effort. Indoor testing is probably a better way to go for both. But we need to get there by going through convoy testing."

And to go through convoy testing, you first have to understand the expectations for today's convoy test as well as the potential expectations for testing analysis.

Convoy testing, Van Gennip said, requires two to four vehicles, one fitted with a set of reference tires. The brand and model for the reference set would be very specific, he said, to ensure that the ETRTO has a wealth of data for a baseline.

From there, you just need to choose a car. Any car.

"As long as the vehicles have the same architectures—as long as they are both rear-wheel drive or front-wheel drive, all-wheel drive, whatever—and as long as they have the same power structures, that they are ICE or EV … you can actually test on different vehicles," Van Gennip said. "And it is almost recommended to do so because tire abrasion—or the rate that you will be losing materials—is going to be directly proportional with how heavy your vehicle is.

"If you are testing on a light vehicle vs. a heavier vehicle, the heavier vehicle will likely wear a lot faster. So if we are coming up with testing regulations for tire manufacturers, we have to decouple that from the vehicle itself. You have to be able to get a set rate that we can apply, regardless of what vehicle is tested."

Throughout the test, it is also important to rotate drivers among the vehicles being tested. Because driving style—like the weight of the vehicle itself—heavily influences tire abrasion.

From there, it's just a matter of seeing how much and how quickly tires are wearing.

"When measuring for TRWP, one of the initial thoughts was: 'Oh, we're measuring tire road wear particles, we need a vehicle to collect all those particles and measure them. Trying to do that on convoy testing would be very difficult for multiple reasons, right?" Van Gennip said. "Trying to collect all of the tire road wear particles? Like, how are you going to ensure that you are getting all of them? How are you going to differentiate between tire particles, brake particles or just road dust? It is going to be very difficult."

That makes mass loss the most effective TRWP abrasion measurement. And that is just a matter of weighing.

First, the tire alone is weighed, then placed on a wheel and weighed again. Once the tires are mounted on the vehicle, it must be ensured that the gas tank or battery is full and then additional weight measurements are taken at each of the four corners of the vehicle.

"You will then start (the test). Weigh at the end. Easy peasy, and then you're done," Van Gennip said.

There are still some questions to be answered regarding how to best tailor convoy testing for any future TRWP standards or testing guidelines. But those will be worked out in time.

"This process is still under development," Van Gennip said. "So please don't go away saying this is exactly what the regulation will be moving forward. This is all still in process, but currently the thought is: If you could measure the weight multiple times throughout, it would give us more data points, right? We would be able to see trends.

"For regulation, though, the thought is you really just need to look at the beginning and the end."

From Van Gennip's perspective, there are some fairly significant flaws with convoy testing. Namely, there are too many uncontrollable variables.

For instance, ambient temperature, weather, road condition and road type vary widely across regions making it difficult to create a level testing field.

"Road conditions alone vary significantly here in the U.S.," Van Gennip said. "… Compare all of these roads to Europe or India or China. Your conditions are going to vary significantly, and while we are trying to take all of that into consideration during these convoy tests, if we are really looking for a real-world standard, I think that needs to be moved to a lab environment."

Moreover, the investments—for both time and finances—are great with on-road testing.

Instead, Van Gennip contends, the industry should be thinking inside the box—bringing the testing to the much-more easily controlled lab environment. For this, there are three practical testing options:

• Internal drum;
• External drum; and
• Flat belt.

"I think there are lots of pros and cons to each option," Van Gennip said.

"The internal drum definitely has a lot going for it. One of those benefits being, if you are testing on the inner surface of the drum, it is much easier to enclose. If you can enclose it, you can do a much better job of doing climactic control and you can also actually capture and measure all those tire road wear particles."

And while there may be a reason for capturing all those particles—for testing for environmental issues for instance—Van Gennip isn't convinced the practice is entirely practical for standard abrasion testing.

But the internal drum method has some drawbacks, too.

Namely, ensuring the accuracy of the test given the inaccuracy of the tire's contact patch.

"Testing on a curved surface will change your contact patch significantly, and it will have a drastic impact not only on contact patch shape, but also on load distribution," Van Gennip said. "If you are looking at a change of load distribution, you are also looking at a change in wear distribution.

"This is all supposed to be measuring wear and if we have a change in wear distribution, is that going to really affect your rate of wear? Maybe. I think that more work would definitely be to be done. But that is where flat belt testing has a bit of an advantage."

Advantage, yes. But disadvantages, too.

Because just as with drum testing methods, there are pros and cons to the flat belt testing. Yes, you ensure a real-world tire contact patch, but mimicking a real-world road surface is rather difficult, which ultimately could impact the accuracy of the results.

"On flat belt testing, now your contact patch most closely resembles what you would see on your real road surface. It is more representative," Van Gennip said. "But on a flat belt machine you are kind of stuck with sandpaper. Sandpaper is very abrasive, that is not what you see on the real road.

"Even still, as I just said, the road conditions vary significantly, so regardless of what method you choose there will have to be some correlation done to get to actual real-world values," Van Gennip said. "But it would probably be a lot closer with the drum over the flat belt."

Either way, Van Gennip said, there are ways to tailor the regulatory tests to adjust for flaws in each. And, ultimately, the deciding factor could come down to cost.

In the end, flat belt machines are more costly and far less accessible.

"If there is going to be an indoor regulation-type test for tire road wear particles, getting it on a drum machine would be more preferable than a flat belt just from a cost standpoint," Van Gennip said.