On wet roads, worn tires with a tread depth of 4/32 inch have an average increased stopping distance of 87 feet for a passenger car and 86 feet for a light truck when compared with new tires, according to a recent study from AAA.
The research explores performance differences on wet pavement between the worn tires and new all-season tires when driving at 60 mph.
Stopping ability is a critical safety function of tires. However, the research findings show that when decelerating from 60 mph to a dead stop, the worn tires continue to advance at an alarming 40 mph — at the point when the new tires have already come to a complete stop.
Tires are also responsible for much of the handling ability of a vehicle. After side-by-side testing, the worn tires accounted for an average 33% reduction in handling ability for a passenger car and 28% percent for a light truck.
The research also explores the link between poor tire tread depth and hydroplaning, a very hazardous situation for any motorist.
The AAA concludes that tires should be replaced once the tire tread depth reaches 4/32 inch — as opposed to frequently recommended industry guidelines and state laws that use 2/32 inch as the replacement standard.
The report also notes that while tire performance varies by brand, price is not necessarily an indicator of quality.
On average, new high-priced tires did not perform significantly better than new low-priced tires as it concerned stopping distance on a wet road surface, maximum lateral acceleration on a wet road surface and NVH characteristics.
Independent testing was conducted at the Michelin's Laurens Proving Grounds in Montville, South Carolina, and later validated at another facility. Due to their popularity in recent years, the Toyota Camry and Ford F-150 served as test vehicles to represent their respective categories. For each vehicle, the most common original equipment tire size was tested.