Auto and Road User Journal
Copyright © 1997 by TranSafety, Inc.
December 17, 1997
(U.S. and Canada)
Fax: (360) 335-6402
A number of states and Canadian provinces have already outlawed studded tires, and others are considering it. The State of Alaska has tested a new winter tire called "Blizzak" developed by Bridgestone and found that it offers an acceptable substitute for pavement-destroying and dust-generating studded tires.
The new tire exceeded the performance of all-season radials in every test category except dry-pavement braking and equaled the performance of studded tires in all categories except stopping and accelerating on ice, where it fell short by between 8 and 15 percent.
Close enough, concluded David Junge and Jian Lu of the University of Alaska's Engineering Department and David Esch of Alaska's Department of Transportation. Their report, "Evaluation of Winter Traction with Different Types of Tires," was published by the Transportation Research Board (74th Annual Meeting, January 22-28, 1995, Paper No. 95 0772).
The report did not discuss the design of the Blizzak tire nor its probable longevity; however, it did describe the performance tests researchers used to compare the new tire with studded tires and all-season radials and the results of those tests.
Blizzak tires were tested against both studded and non-studded all-season tires from Goodyear, Firestone, and Michelin. The tires were mounted on three front-wheel-drive compacts, two full-sized rear-wheel-drive sedans, two full-sized rear-wheel-drive pickups, and a van. The pickups and van had rear-wheel ABS systems; the others had four-wheel ABS.
Researchers conducted the tests at slightly below freezing or near-freezing temperatures on packed snow, glare ice, icy pavement, and bare pavement surfaces afforded by frozen lakes, airport taxiways, and low-volume roads near Anchorage and Fairbanks.
Results varied widely, depending on test site and vehicle type. The front-wheel-drive cars showed the best starting and weakest stopping power of the tested vehicles. When researchers compared the three types of tires, the Blizzaks were superior on packed snow, the studded tires performed best on ice, and the all-season tires excelled on bare pavement.
Stopping. In one test on packed snow, the Blizzaks shortened stopping distances from 25 miles per hour (mph) by as much as 33 percent. On the average, the Blizzak tires performed on packed snow only slightly better than studded tires and non-studded all-season tires. On the big pickups, the Blizzaks actually yielded longer stops.
Under icy conditions, the Blizzaks reduced stopping distances by an average of 8 percent over all-season tires. Studded tires reduced stopping distances by about 17 percent under icy conditions when compared with all-seasoned tires. Average stopping distances from 25 mph were 106 feet for studded tires, 118 feet for Blizzak tires, and 128 feet for all-season tires. These distances were about three times farther than stopping distances on packed snow and 7 to 10 times farther than stopping distances on bare pavement.
In one test near Fairbanks involving a sedan, a station wagon, and a van under generally icy road conditions (as opposed to the glare ice of a Zamboni-smoothed frozen lake, where studded tires performed best), the Blizzaks brought heavy rear-drive vehicles to a stop from 40 mph in 121 feet, as compared with 141 feet for studded tires and 179 feet for all-season tires.
On bare pavement, the Blizzaks showed a 2-35 percent stopping-distance advantage over studded tires. In a test with one full-sized sedan, the studded tires had stopping distances more than 40 percent longer than the Blizzaks or the all-season tires. In some bare-pavement stopping tests, the all-season tires were marginally superior, and in other tests the Blizzak tires excelled.
Starting. On packed snow, the Blizzaks and the studded tires both accelerated to 25 mph between 10 and 20 percent faster than the all-season tires. On ice, the studded tires showed a 29 percent advantage and the Blizzaks a 13 percent advantage over all- season tires. On bare pavement, both Blizzaks and all-season tires were judged marginally superior to studded tires.
Cornering and Hill Climbing. Using sophisticated formulas and g-force measurements, the researchers found no significant differences in cornering power among the three tires.
Nor did the three tires show any significant differences in hill-climbing ability, as calculated from g-force measurements during the accelerations tests. All three tires were deemed capable of ascending a 15-16 percent grade on packed snow and a 10- 12 percent grade on ice.
(December 16, 1997 editor's note: Bridgestone's Blizzak tires are now being advertised on television for winter use.)
Copyright © 1997 by TranSafety, Inc.