Tires provide for steering, traction, braking, and load support by transmitting forces between the vehicle and the road. Lateral force variation (LFV) is a property of a tire that characterizes its dynamic behavior of these forces. High values of LFV for a given tire reflect a high level of manufacturing variations in the tire structure that will impart ride disturbances into the vehicle in the lateral, or steering, direction. LFV is measured according to processes specified by the
ASTM International
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
in ASTM F1806 – Standard Practice for Tire Testing.
LFV can best be explained by example. Assume a perfectly uniform tire mounted on a perfectly round wheel loaded with a constant
force
In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...
against a perfectly round test wheel. As the wheel turns, it turns the tire, and the tire carcass undergoes repeated deformation and recovery as it enters and exits the contact area. If we measure the lateral force between the tire and the wheel we will see zero change as the tire turns. If we now test a typical production tire we will see the lateral force vary as the tire turns.
Consider a good tire with LFV of 4 pounds. This tire will induce a 4 pound force sideways into the vehicle every rotation. The frequency of the force will increase in direct proportion to rotating speed. This effect will influence the steering of the vehicle. Tire makers test tires at the point of manufacture to verify that the LFV is within allowable quality limits. Tires that exceed these limits may be scrapped or sold to markets that do not require stringent quality.
Waveform analysis
LFV is a complex waveform. It is expressed using several standard methods, including peak-to-peak, first harmonic, second harmonic, and higher-order harmonics. In production LFV testing these are reported as both magnitudes and angles.
See also
*
Cornering force
Cornering force or side force is the lateral (i.e., parallel to wheel axis) force produced by a vehicle tire during cornering.
Cornering force is generated by tire slip and is proportional to slip angle at low slip angles. The rate at which ...
*
Camber thrust
Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch. Camber thrust is generated when a point on the outer surface ...
*
Traction circle
External links
* http://www.freepatentsonline.com/3946527.html
Tires
{{automotive-tech-stub