Rim Joining Methods
There are three methods used to join the ends of rims after rolling. The three methods are pinning, sleeving, and welding
This method consists of joining the ends of the rim with a steel pin inserted into a cavity on both sides of the rim extrusion. These steel pins are about four millimeters in diameter, two inches in length, with pointed ends. .The extrusion shape for the rim is made with the pin cavities extruded in place, usually just under the tire bead on each side of the rim. The diameter of these holes is closely controlled to properly press fit over the pin. The rim is assembled by injecting a measured amount of epoxy glue in each rim pin hole, then inserting the pin ends in the holes. The rim is then placed in a machine that constricts the diameter of the rim by means of a band around the outside of the rim and a hydraulic cylinder that pulls the ends of the band together. This force causes the rim ends to be forced over the pins, closing the joint.
This method of rim end joining is done in the same way as the pinning process, but uses an extruded aluminum insert matching the inner profile shape of the rim rather than pins. The sleeving method is usually used on rims that are lighter and considered to be of higher quality than pinned rims. The sleeve is typically about three inches in length. After cutting the sleeve blank off the extrusion, it is formed in a die to give it a radius to match the rim. The ends are also tapered to facilitate insertion in the rim voids. The joint is closed with the same constricting machine and glue process as described in the pinning method above.
The welding method is used on all levels of rims from OEM high volume rims to high quality after market rims. The method typically used is called a “flash-butt process”. The process is done in a large welder that grips the ends of the rim in clamps to hold and guide the rim during welding. The rim blank is rolled and cut with extra length circumferentially. The rim is clamped in the welder dies with the ends of the rim protruding about ¼” from the die on each side. The welder then starts the “flash” part of the weld cycle. It passes very high amperage current through the clamp dies while slowly moving one die to bring the ends of the rim together. The current creates an arc between the ends of the rim, burning off the extra metal allowed in the cutting of the rim blank while heating the ends of the rim. After a precisely controlled flash time, the current is turned off and the “butt” part of the weld cycle is initiated. This consists of rapidly forcing the heated ends of the rim together with great force to complete the joint. There is weld flash left around the weld that is removed to smooth the joint and blend it in to the extrusion shape.
Eyelets are reinforcements that are set into the rim spoke holes. They function to help obtain even spoke tensions during wheel build and to reinforce the rim spoke face area at the nipple contact point. Eyelets are typically made of nickel plated brass, but also are made of plated mild steel and stainless steel.
There are two types of eyelets, single and double. Single eyelets are the most common, set in the spokeface of the rim only. A double eyelet consists of a single eyelet as in the previous description along with a formed cup that has a lip at the top to engage the tire well wall of the rim. At the bottom of this cup is a hole of correct size to receive the eyelet in the rim spoke face. The cup is inserted through the clearance hole in the rim tire well wall and locked in place with the conventional single eyelet through the cup and rim spoke face. This eyelet/cup combination distributes the load of spoke tension over both the spoke face and the tire well wall of the rim. For this reason, thinner walls can be extruded to make a lighter rim while not risking having an eyelet pull through the spokeface as it might if it were a single eyelet.
Eyelets make it easier to obtain even spoke tension by reducing the friction of turning the nipple because the eyelet is harder than the aluminum rim. Without an eyelet, there is a high resistance to turning the nipple against the sharp, softer edge of the aluminum spoke hole. This problem is especially evident when spoke tension is being set with nipple torque reading devices.
Eyelets are usually inserted in the rim after any finishing processes.
There are typically two types of valves found on bicycle wheels, the Presta, or European, and the Schrader, or American valve. The Presta requires a smaller hole (6.2mm) in the rim than does the Schrader (8.3mm). The smaller Presta valve has the advantage of being able to be used in narrow and aero rim sections without compromising the strength of the rim at the valve hole.
The most common rim finishes are anodizing, plating, coating, and polishing.
Anodizing is somewhat unique in that it is not an applied coating. It is a process that uses electric current in baths that cause the top layer of the metal to convert to an oxide. The rim is first washed and then etched to clean the metal and remove surface contaminations. It is then anodized to create a protective oxide surface layer. If a color is desired, the rim can then be dipped in a color bath that is absorbed into the rim oxide. Sealing and drying operations follow to complete the process.
Plating is a process using electric current in a bath to deposit a coating on the surface of the rim. The plating is carried to the rim from a source in the bath by the movement of the electric current from the source to the rim. Chrome plating is the most common finish done to aluminum rims in this process. A base coat of nickel is put on the rim first by the described method, followed by a thin flash of chrome that is only tenths of a thousandth of an inch thick. The nickel undercoat is actually the protective part of the plating. The flash coating of chrome is put on to create the shiny finish.
Rim coatings are usually paint or powder coatings. Paint is common enough to be self-explanatory. In the powder coating process, the rim is cleaned, then the powder coating is applied to the rim with a spray gun that coats the rim with an even layer of powdered material. The rim is then heated in an oven under carefully controlled conditions to melt the powder, creating a solid coating on the rim.
A multitude of colors are available in both the paint and powder coating methods of rim finishing.
Polishing is done in a machine that spins the rim while utilizing polishing wheels to finish the aluminum with a compound on the wheel. The finish can be controlled by the composition of the wheel. A different finish can be applied to different areas of the rim by using different composition wheels on each area. In this way, the brake tracks can have a buffed finish while the spoke face is bright polished.
ERD is the abbreviation for Effective Rim Diameter. This is the diameter of the rim derived at the point the ends of the spokes should come to when in the built wheel. This is the diameter calculated when wheel builder’s tools such as measuring rods are used for developing spoke lengths for the particular hub and rim combination to be built.
RIM SECTION HEIGHT:
Section height is the overall height of the rim profile from the outer spokeface to the top of the section.
RIM TIRE WELL:
The tire well of a rim is the inside of the rim profile between the rim sidewalls where the tire and tube are seated. The depth and design of this well determines the ease of mounting the tire and the seating and retention of the tire on the rim.
The beads of a rim are the protruding ribs at the top inside of the rim’s tire well sidewalls. These ribs engage the groove just above the bead of a tire to help keep it in place on the rim.
RIM BEAD SEATS:
The bead seats of a rim are the angled areas at the inner bottom sides of the tire well wall. This area is where the vertical side of the rim inner sidewall under the beads transitions to an angle toward the center of the tire well. The bead of the tire rests on this surface when inflated to also help center and retain the tire.
RIM TIRE WELL:
RIM DIAMETERS AND SIZES
Rim diameters and sizes are usually specified in two ways, metric and inch. Rims will have a specification like “559mm, 26”. The metric diameter is measured at the rim bead seat. The inch dimension represents the nominal outside diameter of the inflated tire when mounted on the same rim.
This is the abbreviation for “European Tire and Rim Technical Association”. This association is the European standards association that published reference manuals listing tire and rim specifications. These specifications are to be used as guides for designing rims and tires to assure proper compatibility.
This is the abbreviation for Japanese Industrial Standard. This is a Japanese standard publication with a heavy focus on testing and design criteria for all bicycle components.