Why all partially worn tires aren't created equal
Michelin says standardized testing of part-worn tires will improve safety, cut down on premature replacement and save money.
Michelin is one of the world's premier tire manufacturers. In the performance car realm, it's the exclusive supplier to the C7 Chevrolet Corvette, are the company's tires are included in optional go-faster packages for the Ford Mustang, plus they outfit many of Porsche's more ballistic 911 models.
On the less glamorous, but still important end of the spectrum, the French company also prides itself on producing long-lasting all-season tires that deliver good performance not only when new, but all the way up to the end of their usable life for regular run-of-the-mill vehicles. According to the National Highway Traffic Safety Administration, the end of the road for a tire is when it reaches 2/32-inch tread depth.
Since tires are in new condition for only a short time, Michelin is spearheading an initiative to have standardized worn tire testing instituted to supplement existing tests that focus on new tire performance. With the addition of worn tire test data, the hope is to arm consumers with more information to hammer home the point that not all tires are created equal and to help prevent the wasting of resources and money from premature tire replacements. Michelin says that 400 million tires are unnecessarily removed early, with most heading to landfills and costing drivers more than $25 billion globally each year.
Michelin hopes worn tire testing becomes an industry standard.
To display the difference in performance between all-season tires in both new and worn condition, Michelin invited us down to its Laurens Proving Grounds in South Carolina. There we tested two mystery subjects that were simply referred to as the Brand A and Brand B tires with their sidewall lettering shaved to protect their identities.
Michelin's definition for a worn tire is at when it is at the end of its usable life, which for the test included radials buffed down to 3/32-inch tread depth, puting them just above the wear bars. Michelin acknowledges that buffed tires aren't a completely accurate representation of a typical worn tire subjected to varying road conditions, vehicle alignments and weather. But they are ideal for this scenario, allowing each to perform to their optimal capabilities.
Two exercises awaited us, including a braking test in Toyota Camry sedans and a short handling course behind the wheel of Nissan Juke crossover SUVs. To make things more interesting, both tests would be on wet surfaces with 1 millimeter of flowing water. The Brand A tire in new condition stopped from 45 mph in 81.2 feet, and 91.6 feet worn, which works out to roughly a 10-foot difference. The Brand B tire came to a stop in 99.3 feet new and 127.5 feet worn, a performance drop-off of nearly 30 feet, which is substantial. Interestingly, the worn Tire A outperformed a new Tire B.
Web braking tests reveal a drastic difference between the tires in both new and worn condition.
At the wet handling course that included a variety of turns, slalom and light and hard braking areas, we hopped into front-wheel drive Jukes. The new A tire provided sharp turn in, lots of grip and a planted back end. B wasn't as surefooted, being quicker to understeer and have the rear step out around turns, causing stability control to cut in.
The difference on the worn tires here was even clearer. The A tire displayed a noticeable decline in grip, but was still impressively capable and comfortable motoring around the wet tarmac. Performance fall off for B was more drastic, resulting in a lot of slipping and sliding at turn in, through the turns and when powering out of corners requiring a more careful driving styling.
At the end of the day, the Brand A tire was revealed to be the Michelin Premier A/S and the Brand B was the Goodyear Eagle Sport A/S. Prior to the reveal, Michelin discussed the key components for maintaining traction throughout a tire's life, which are rubber compound, contact patch and tread design. It was interesting to hear about silica-infused rubber and an oval-shaped contact being optimal for grip and even wear characteristics, but the tread design aspect was the most visual.
On the Michelin, in both new and worn condition, its contact patch has 44 biting edges, since the tread grooves, known as sipes, go throughout the entire tread blocks. For the Goodyear, there are 35 biting edges when new, which decrease to 10 in worn condition, because the sipes don't run through the entire block. The width of the tire ribs also differ between the two test subjects with the Premier's getting wider to help better evacuate water as tread depth disappears, while the Eagle Sport's ribs become narrower over time.
Tire Rack's Director of Tire Information Woody Rogers agrees with Michelin in its claims that performance of some tires change more than others over their lifespan. There should be worn tire testing, he agrees, but he believes that its proposed procedures need some refinement.
"The trick is to find the right thing that is meaningful for evaluating what a customer will find at the end of a tire's life. What they want to know is how it will perform in three or four years," says Rogers. "In its current form, it's not there yet." The affects of road conditions and weather are not accounted for when testing buffed tires.
Michelin's worn testing procedures could use some refining according to Tire Rack's Woody Rogers.
Rogers also points out that while quality tires designed to perform well in the wet at low tread depths will work for drivers in certain parts of the country, there is a significant change in wet performance as tires wear away the last 1/32 of tread, going from 3/32 down to 2/32 remaining depth. And people who live in areas that experience real winters may not be inclined to keep tires until they get to the wear bars because the lack of tread depth makes it difficult to cope with incompressible liquids such as snow and slush.
If anything comes of Michelin's efforts to implement standardized worn tire testing remains to be seen, but give it credit for trying to start the conversation about it. Worn tire test data would provide consumers more information to separate the good tires from the not-so-good tires to make for more informed tire purchases.
Either way, it's important to do your homework when it comes time to purchasing new tires, because they aren't all created equal. They're arguably the most important performance and safety feature on a car -- they're the only thing directly connecting it to the road.