Traction,traction force ortractive force is aforce used to generatemotion between a body and a tangential surface, through the use of eitherdry friction orshear force.[1][2][3][4]It has important applications invehicles, as intractive effort.
Traction can also refer to themaximum tractive force between a body and a surface, as limited by available friction; when this is the case, traction is often expressed as the ratio of the maximum tractive force to thenormal force and is termed thecoefficient of traction (similar tocoefficient of friction). It is the force which makes an object move over the surface by overcoming all the resisting forces likefriction, normal loads (load acting on the tiers in negativeZ axis),air resistance,rolling resistance, etc.
Traction can be defined as:
a physical process in which a tangential force is transmitted across an interface between two bodies through dry friction or an intervening fluid film resulting in motion, stoppage or the transmission of power.
— Mechanical Wear Fundamentals and Testing, Raymond George Bayer[5]
In vehicle dynamics,tractive force is closely related to the termstractive effort anddrawbar pull, though all three terms have different definitions.
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Thecoefficient of traction is defined as the usable force for traction divided by the weight on the running gear (wheels, tracks etc.)[6][7] i.e.:
usable traction =coefficient of traction ×normal force.
Traction between two surfaces depends on several factors:
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In the design of wheeled or tracked vehicles, high traction between wheel and ground is more desirable than low traction, as it allows for higher acceleration (including cornering and braking) without wheel slippage. One notable exception is in the motorsport technique ofdrifting, in which rear-wheel traction is purposely lost during high speed cornering.
Other designs dramatically increase surface area to provide more traction than wheels can, for example incontinuous track andhalf-track vehicles.[citation needed] A tank or similar tracked vehicle uses tracks to reduce the pressure on the areas of contact. A 70-ton M1A2 would sink to the point of high centering if it used round tires. The tracks spread the 70 tons over a much larger area of contact than tires would and allow the tank to travel over much softer land.
In some applications, there is a complicated set of trade-offs in choosing materials. For example, soft rubbers often provide better traction but also wear faster and have higher losses when flexed—thus reducing efficiency. Choices in material selection may have a dramatic effect. For example: tires used for track racing cars may have a life of 200 km, while those used on heavy trucks may have a life approaching 100,000 km. The truck tires have less traction and also thicker rubber.
Traction also varies with contaminants. A layer of water in thecontact patch can cause a substantial loss of traction. This is one reason for grooves andsiping of automotive tires.
The traction of trucks, agricultural tractors, wheeled military vehicles, etc. when driving on soft and/or slippery ground has been found to improve significantly by use of Tire Pressure Control Systems (TPCS). A TPCS makes it possible to reduce and later restore the tire pressure during continuous vehicle operation. Increasing traction by use of a TPCS also reducestire wear and ride vibration.[9]