Auto Service World
Feature   May 1, 2014   by Emily Atkins, Reprinted from PurchasingB2B/Fleet Management

Safe Stopping

Tire technology advances in the wet

Car control in wet conditions is fundamental to safety, and yet when tires wear they tend to lose traction as the grooves get shallower and the tread gets thinner.

Michelin is seeking to remedy this problem with a new tire design that maintains its traction qualities as it wears. And in a graphic demonstration, they showed that, indeed, their half-worn tire can have better stopping power and better wet traction than their competitors’ tires.

To demonstrate the qualities of their new Premier All Season tire, the manufacturer let a group of auto journalists loose on their Laurens Proving Ground test track facility just outside of Greenville, South Carolina. Two sets of exercises were set up to show the tire’s capabilities: wet braking and wet handling.

In the wet handling exercise, test drivers took four cars out, each shod with a different set of tires—new Premier A/S, half worn Premier A/S and two different brand-new competitor tires. The cars were all Cadillac CTSs, a model appropriate for the tire, Michelin said.

The handling track is a purpose-built wet skid pad zone at the Proving Ground, equipped with enough sprinkler nozzles to simulate monsoon conditions. The course was designed with a slalom section for quick directional changes, a couple slower corners, and a straightaway to test hydroplaning and hard braking. It was a challenging drive and provided plenty of opportunity for subjective comparisons of the tires.

The difference between the Michelins and the competitors was evident, especially in the amount of hydroplaning and cornering grip they afforded. The Caddys all had their traction control turned off, but stability control on, and with the Michelins the stability systems activated far less often when the car was pushed.

But as much as the subjective testing on the skid pad showed a difference among the tires tested, it was in the objective test—wet braking—that the Premier A/S really proved itself. The half-worn Michelins went up against brand new Bridgestone and Goodyear tires in an electronically measured stop from highway speed on a uniformly wet track.

The Premier A/S consistently stopped a car length shorter than the other two tires. These results were consistent across the pool of drivers performing the tests.

So, how did Michelin design a tire that has so much more grip when it’s half used up?

The secret is in the compound and the moulding technology. Michelin calls it Evergrip, emphasizing that the tire “evolves” rather than just “wearing”. The grooves in the rubber that evacuate water from the contact patch are inverted V-shapes, so they get wider as the tire wears down. As well, hidden grooves appear only as the tire erodes. The tires are compounded with high levels of silica, which gives extra grip, and sunflower oil, for improved cold weather flexibility.

The new tires are available now through regular distribution channels. Michelin says pricing is slightly above the Tier 1 average.

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