The rim is the "outer edge of a wheel, holding the tire". It makes up the outer circular design of the wheel on which the inside edge of the tire is mounted on vehicles such as automobiles. For example, on a bicycle wheel the rim is a large hoop attached to the outer ends of the spokes of the wheel that holds the tire and tube. In cross-section, the rim is deep in the center and shallow at the outer edges, thus forming a "U" shape that supports for the bead of the tire casing. In the 1st millennium BC, an iron rim was introduced around the wooden wheels of chariots to improve longevity on rough surfaces.
Characteristics
Design: The first pneumatic tires for bicycles were simple tubes in shape secured to the wooden outer concave surfaced circumference of the wheel by glue and air pressure pressing them against it. The surface for receiving the tube was not very secure thus causing the tires to sometimes come off the rims. Bicycle manufacturer and inventor, Thomas B. Jeffery, developed an improved tire with a wire that was embedded in the rubber of the tire, and the wire could be tightened onto the rim. His 1882 patent became the ancestor of all clincher tires, the design found on modern bikes and cars. Contemporary clincher tires today have wires embedded on both beads of the tire so wires fit inside the edges of the rim to hold the tire in place when it is fully inflated.
Diameter : distance between the bead seats, as measured in the plane of the rim and through the axis of the hub which is or will be attached, or which is integral with the rim.
Width : separation distance between opposed rim flanges. The flange-to-flange width of a rim should be a minimum of three-quarters of the tire section width. And the maximum rim width should be equal to the width of the tire tread.
Type: Depends on the type of vehicle and tire. There are various rim profiles, as well as the number of rim components.
Material: Various metals can be used for the rim. Commonly seen are alloy, mag, aluminum, and chrome. Teflon coatings are sometimes also applied for an extra layer of protection.
Vehicle performance: Because the rim is where the tire resides on the wheel and the rim supports the tire shape, the dimensions of the rims are a factor in the handling characteristics of a vehicle. For example:
Production
A standard automotive steel wheel rim is made from rectangular sheet metal. The metal plate is bent to produce a cylindrical sleeve, and then the two free edges of the sleeve are welded together. At least one cylindrical flow spinning operation is carried out to obtain the desired thickness profile of the sleeve—and the desired angle of inclination relative to the axial direction in the zone for the outer seat. The sleeve is then shaped to obtain the rims on each side with a radially inner cylindrical wall in the zone of the outer seat and with a radially outer wall inclined at an angle corresponding to the standard inclination of the rim seats. The rim is then calibrated. To support the cylindrical rim structure, a disc is made by stamping a metal plate. It has to have appropriate holes for the center hub and lug nuts. The radial outer surface of the wheel disk has a cylindrical geometry to fit inside the rim. The rim and wheel disk are assembled by fitting together under the outer seat of the rim and then being welded together. The disk is welded in place such that the center of the wheel is equal to the center of the hub. The distance between the centerline of the rim and the mounting plane of the wheel is called the "offset" and can be positive, negative, or zero. One-piece rim and wheel assemblies may be obtained by casting or forging.
Meaning
In discussions of automobiles, the terms wheel and rim are often incorrectly used synonymously, as in decorative wheels being called rims. The rim is more-clearly just a component of a bicycle wheel, and it can be purchased separately and replaced if damaged. Used broadly, or used figuratively, the wordrim can mean the outer edge of any circular object. Some authors are careful to use rim for only the outer portion of a wheel, where the tire mounts, just as the rim of a coffee cup or a meteor crater does not refer to the entire object. One engineering text says "alloy wheels often incorrectly called aluminum rims". Others use rim to mean the entire metal part to which the tire mounts, because the rim and the wheel are often cast or stamped from a single piece of metal instead of being distinct as with wire wheels. At the same time, "wheel" may refer to the entire rotating assembly, including the tire.
Railroad usage
In railroad usage, the conical running surface of the wheels may be called a rim, a wheel tread or a tyre.
Historical Development
Early wheels of motor vehicles started with bicycle wheels with the rims attached to the central axle by spokes. As vehicles became heavier wood-spoked wagon wheels with steel rims were used. Later solid rubber tires were mounted on the rims of the wooden wheels. Some wooden automobile wheels had a demountable steel rim which was bolted on to the outer circumference of the wooden wheel. Wheels which were completely made of metal gradually became widespread around the 1930's.
