# Rolling friction

Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when an object such as a ball or tire rolls. It is caused by the deformation of the wheel or tire or the deformation of the ground. It depends very much on the material of the wheel or tire and the sort of ground. For example, rubber will give a bigger rolling resistance than steel. Also, sand on the ground will give more rolling resistance than concrete. A vehicle rolling will gradually slow down due to rolling resistance, but a train with steel wheels running on steel rails will roll much further than a car or truck with rubber tires running on pavement, even when differences in mass and momentum are accounted for. The coefficient of rolling resistance is generally much smaller for tires or balls than the coefficient of sliding friction.[1]

## In braking

It is worth noting that for all vehicles that travel on wheels (such as cars and bicycles), the sum of rolling resistance and static friction is what causes the vehicle to slow when the brakes are applied. The actual force applied in braking (for example, clamps applied to disk brakes) is internal, and by Newton's First Law cannot cause a change in the vehicle's motion. Therefore the slowing is caused by contact between the road and the car's tires; the static friction force between road and tire is the "equal and opposite reaction" specified in Newton's Third Law. Rolling resistance can be compared to sliding friction, as when the brakes "lock up", the wheels slide upon the driving surface and do not sufficiently slow the car. Maximum braking force occurs when there is about 11% slip between the wheel's speed and the road - this is used to advantage in ABS braking systems, and cadence braking, a manual technique which achieves something similar.

## Factors that contribute

Several factors affect the magnitude of rolling resistance a tire generates:
• Material - different fillers and polymers in tire composition impact rolling resistance. The replacement of some carbon black with higher-priced silica–silane is one common way of reducing rolling resistance.[2]
• Dimensions - rolling resistance is related to the flex of sidewalls and the contact area of the tire. For example, at the same pressure wider bicycle tires have less flex in sidewalls and thus lower rolling resistance (although higher air resistance).
• Extent of inflation - Lower pressure in tires results in more flexing of sidewalls and higher rolling resistance. This energy conversion in the sidewalls increases resistance and can also lead to overheating and may have played a part in the infamous Ford Explorer rollover accidents.
• Over inflating tires (such a bicycle tires) may not lower the overall rolling resistance as the tire may skip and hop over the road surface. Traction is sacrificed, and overall rolling friction may not be reduced as the wheel rotational speed changes and slippage increases.
• Sidewall deflection is not a direct measurement of rolling friction. A high quality tire with a high quality (and supple) casing will allow for more flex per energy loss than a cheap tire with a stiff sidewall. Again, on a bicycle, a quality tire with a supple casing will still roll easier than a cheap tire with a stiff casing. Similarly, as noted by Goodyear truck tires, a tire with a "fuel saving" casing will benefit the fuel economy through many casing lives (i.e. retreading), while a tire with a "fuel saving" tread design will only benefit until the tread wears down.
• Tread thickness has much to do with rolling resistance. The thicker the tread, the higher the rolling resistance. Thus, the "fastest" bicycle tires have very little tread and heavy duty trucks get the best fuel economy as the tire tread wears out.
• Hard steel rails last longer but may also have lower static friction. They may also suffer fatigue cracking because the cracked area is not worn away by the passing trains.
• Smaller wheels, all else being equal, have higher rolling resistance than larger wheels.[3]

## Physical formula and tables

The force of rolling resistance is given by:

::where
::: F is the resistant force,
::: Crr is the rolling resistance coefficient or coefficient of rolling friction (CRF), and
::: is the normal force.

In usual cases, the normal force on a single tire will be the mass of the object which the tires are supporting divided by the number of wheels, plus the mass of the wheel, times the gravitational acceleration (9.81 mÂ·s−2 on Earth). In other words, the normal force is equal to the weight of the object being supported.

Table of Crr examples: [1]

 Crr description 0.001 to 0.0025 train steel on steel with tatz-mounted electric traction. 0.001 is considered to be the theoretical limit achievable. 0.0015 to 0.0025 low resistance tubeless radial tire used for solar cars/eco marathon cars as specially made by Michelin 0.005 tram-rails standard dirty with straights and curves 0.0055 Typical BMX bicycle tire used for solar cars 0.006 to 0.01 low rolling resistance car tire on a smooth road   and truck tires on a smooth road 0.010 to 0.015 ordinary car tires on concrete 0.020 car on stone plates 0.030 car/bus on tar/asphalt

For example on the earth a car of 1000 kg on asphalt will need a force of 300 N for rolling.

## Effects of

Rolling friction generates heat and sound energy, as mechanical energy is converted to these forms of energy due to the frictional contact. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process which generates heat and sound as by-products.[4] The heat generated raises the temperature of the frictional surface; moreover, this temperature increase typically has an effect upon the coefficient of friction itself.[5]

## References

1. ^ Peck, William Guy. (1859.) "Elements of Mechanics: For the Use of Colleges, Academies, and High Schools". A.S. Barnes & Burr: New York, page 135. Retrieved on 2007-10-09.
2. ^ "Tires and Passenger Vehicle Fuel Economy: Informing Consumers, Improving Performance -- Special Report 286." National Academy of Sciences, Transportation Research Board, 2006. Retrieved on 2007-08-11.
3. ^ VREDESTEIN Bicycle Tires. Retrieved on 2006-08-14.
4. ^ [2] C. Michael Hogan, Analysis of Highway Noise, Journal of Soil, Air and Water Pollution, Springer Verlag Publishers, Netherlands, Volume 2, Number 3 / September, 1973
5. ^ Gwidon W. Stachowiak, Andrew William Batchelor, Engineering Tribology, Elsevier Publisher, 750 pages (2000) ISBN 0750673044

Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or
Tires or tyres (see American and British English spelling differences) are pneumatic enclosures used to protect and enhance the effect of wheels.

Tires are used on all types of vehicles, from cars to earthmovers to airplanes.
Natural rubber is an elastic hydrocarbon polymer that naturally occurs as a milky colloidal suspension, or latex, in the sap of some plants. It can also be synthesized. The entropy model of rubber was developed in 1934 by Werner Kuhn.
Steel is an alloy consisting mostly of iron, with a carbon content between 0.02% and 1.7 or 2.04% by weight (C:1000–10,8.67Fe), depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese and
Sand is a granular material made up of fine mineral particles. It is a naturally occurring, finely divided rock.

Sand comprises particles, or granules, ranging in diameter from 0.0625 (or 116 mm) to 2 millimeters.
Concrete is a construction material that consists of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel limestone or granite, plus a fine aggregate such as sand or
Vehicles are non-living means of transport. They are most often man-made (e.g. bicycles, cars, motorcycles, trains, ships, and aircraft), although some other means of transport which are not made by man can also be called vehicles; examples include icebergs and floating tree trunks.
train is a series of rail vehicles that move along guides to transport freight or passengers from one place to another. The guideway (permanent way) usually consists of conventional rail tracks, but might also be monorail or maglev.
Steel is an alloy consisting mostly of iron, with a carbon content between 0.02% and 1.7 or 2.04% by weight (C:1000–10,8.67Fe), depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese and
Rail tracks are used on railways (or railroads), which, together with railroad switches (or points), guide trains without the need for steering. Tracks consist of two parallel steel rails, which are laid upon sleepers (or cross ties) that are embedded in ballast to form the
automobile (from Greek auto, self and Latin mobile moving, a vehicle that moves itself rather than being moved by another vehicle or animal) or motor car (usually shortened to just car) is a wheeled passenger vehicle that carries its own motor.
truck is a vehicle usually used for transporting bulk goods, materials, or equipment. The word "truck" comes from the Greek "trochos", meaning "wheel". In America, the big wheels of wagons were called trucks.
Sliding friction is when two solid surfaces slide against each other. Putting a book flat on a desk and moving it around is an example of sliding friction. Factors affecting sliding friction include weight (normal force) and the stickiness of the two surfaces.
wheel is a circular device capable of rotating on its axis, facilitating movement or transportation or performing labour in machines. A wheel together with an axle overcomes friction by facilitating motion by rolling. Common examples are found in transport applications.
racing bicycle is built using lightweight, shaped aluminium tubing and carbon fiber stays and forks. It sports a drop handlebar and thin tires and wheels for efficiency and aerodynamics.
Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or
brake is a device for slowing or stopping the motion of a machine or vehicle, or alternatively a device to restrain it from starting to move again. The kinetic energy lost by the moving part is usually translated to heat by friction.
disc brake is a device for slowing or stopping the rotation of a wheel. A brake disc (or rotor in U.S. English), usually made of cast iron or ceramic, is connected to the wheel or the axle.
Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body, first compiled by Sir Isaac Newton.
Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or
Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body, first compiled by Sir Isaac Newton.
Sliding friction is when two solid surfaces slide against each other. Putting a book flat on a desk and moving it around is an example of sliding friction. Factors affecting sliding friction include weight (normal force) and the stickiness of the two surfaces.
An anti-lock braking system (ABS) (translated from German, Antiblockiersystem) is a system on motor vehicles which prevents the wheels from locking while braking. The purpose of this is to allow the driver to maintain steering control under heavy braking and, in some
Cadence braking is a technique used to allow a car to both steer and brake on a slippery surface. It would normally be used to effect an emergency stop where traction is limited, though for use in an emergency requires a presence of mind that the situation itself might preclude.
Ford Explorer is a mid-size sport utility vehicle sold in North America and built by the Ford Motor Company since 1990. It's manufactured in Louisville, Kentucky (it was also assembled in Hazelwood, Missouri until the plant closed on March 10, 2006).
neutrality is disputed.
* It may require general cleanup to meet Wikipedia's quality standards.
The tread of a tire or caterpillar track refers to the rubber on its circumference that makes contact with the road. As tires are used, the tread is worn down limiting their effectiveness in providing traction.
Friction is the force of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or

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Mechanical failure modes
Buckling
Corrosion
Creep
Fatigue
Fracture
Melting
Thermal shock
Wear
Yielding