What Causes Feathered Tires?by Richard Rowe
"Toe setting" may seem like one of those obscure terms relevant only to engineers and mechanics, but it's actually quite germane to soccer moms, business travelers and anyone else who uses an automobile. The ability to read tire wear, including conditions such as feathering, is a key skill that almost anyone can acquire, and it may well save you more than money -- it could some day save your life.
The wheels on your car may look perfectly square with the car from a distance, but they're not. Tires both sit at and go through a whole range of angular movements: they tilt in or out at the top, move forward or backward with the suspension and angle inward toward each other, or outward away from each other, at the front. This last setting is known as the suspension's "toe" setting. "Toe-in" means the front of the tires point toward each other, and "toe-out" means that they point away from each other.
Toe Settings and Slip Angle
You may wonder why a manufacturer would want your vehicle's wheels to point anything but completely parallel with each other; after all, that would offer the least rolling resistance and best fuel economy. But tires work best when they're slipping a little relative to the road. A slight slip angle keeps the tires warm and the tread sticky, while zero angle makes them cold and hard. Excess slip angles can overheat your tires at sustained high speeds, quite possibly resulting in tread disintegration or a blowout.
Toe Angle and Steering Dynamics
Another reason for changing toe angle from the parallel is related to how it affects steering. Setting the suspension with a toe-in or inward angle causes the wheels to constantly steer toward each other, which makes that end of the car more stable and resistant to sudden changes in steering input. Angling the tires away from each other does the opposite: increasing steering response, but making that end of the car more unstable. At their extremes, toe-in can make the car handle like a dump truck and refuse to turn, while toe-out can make it darty and unpredictable.
Reading the Feather
Feathering happens as a result of the tire's sideways slip. As the tire turns sideways, the road grinds on the tread, causing one side to wear faster than the other. Radial tires like those used on most cars tend to roll a little under excess toe, which means the side of the tread with more wear is the one facing the front of the car. Tire wear facing the outside of the tire indicates excessive toe-in, while feathering facing the inside of the tire indicates toe-out.
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