A typical aftermarket cush-drive...
A typical aftermarket cush-drive setup utilizes small rubber donuts. These must be inspected and replaced regularly, as they are much smaller than the stock parts.
Which recipe is right for you?
Not too long ago, things were simple if you wanted to upgrade your scoot with aftermarket hoops: Call up your favorite supplier of Italian cast magnesium wheels, wait several weeks for the wheels to arrive, bolt them on and go. Now, with a wide variety of materials and forming techniques to choose from, selecting the right wheel for the job can be a daunting task.
The stock wheels on your bike are almost certainly made from cast aluminum-though there will be a smattering of other materials mixed in to enhance its properties appropriately. Aluminum, plentiful and easy to work with, offers a good compromise of cost for manufacturing, and strength and elasticity for the road hazards a streetbike encounters. Casting is the most economical way to form bare aluminum into the convoluted wheel shape. Molten material is poured into molds-usually made from sand-and left to cool. Excess material is cut away, and important areas like the hub and tire interface are machined smooth and true.
Suzuki cush drive is larger...
Suzuki cush drive is larger and heavier, but much easier on your drivetrain.
Spun aluminum wheels take shape from sheet stock. The two halves of the rim and spokes begin as flat discs, which are then "spun" into shape on a mandril and welded together. The machined hubs are then bolted or welded to the spokes.
One way to increase a wheel's strength-or parlay that increased strength into decreased weight-is to forge the material into shape. Forging requires huge investments in tooling, as the process involves tremendous amounts of force-a chunk of raw material is pressed into the desired form between two or more dies, much as you would squish a ball of plasticene into a pancake between your hands. The formed part is then heat-treated and, as with casting, excess material is machined off. Forging results in a stronger finished product than casting, as the grains of the material can be oriented in a desired direction rather than randomly placed. Because the dies for forged wheels are so expensive, many manufacturers will have a limited number, and use small machined bolt-on carriers to adapt the various disc and sprocket hole patterns; check for this when looking for wheels, as it does add weight and sacrifice a bit of strength.
Substituting magnesium in the casting or forging process is an easy way to shed pounds from the wheel, as magnesium (the origin of the term "mag" wheels) is approximately two-thirds the density of aluminum. That light weight comes with several disadvantages, however. One is the cost of the raw material and the caution required to work with it-pure magnesium will burn quite nicely. Another is the material's strength and elasticity properties: Magnesium has a lower tensile strength-the material's resistance to being torn apart-than aluminum, as well as a lower modulus of elasticity-a measure of its ability to return to its original shape when distorted. While desirable in racing for their light weight, magnesium wheels are more susceptible to damage from hitting debris in the road than aluminum hoops.
Moving away from metals, carbon fiber is even less dense than magnesium, and much stronger and stiffer than either magnesium or aluminum. The fiber weaves can also be laid in a specific direction, enhancing strength. Fabricating carbon-fiber wheels is a tedious process-a wheel is a much more intricate shape than, say, a fairing-and the machined metal hubs must be bolted or glued to the wheel. One drawback of carbon fiber is that its extreme stiffness makes it less pliable under impact-rather than deform, it could delaminate or even break. In some cases where a damaged aluminum or magnesium wheel could be repaired in a press, a carbon-fiber wheel could appear fine but be unsafe to use. Even though recent advances in their manufacture have greatly improved reliability, carbon wheels remain illegal in many racing organizations.
When shopping for wheels, there are a number of items to check for aside from the material and method of manufacture. Commonly, any spacers should be captive in oversized bearings rather than loose. Make sure valve stems are included, and see if the wheel accepts the stock sprocket or needs something special-like the majority of wheels here. And if you are concerned about drivetrain wear, take a look at the wheel's cush drive-most of the wheels tested, unless otherwise noted, have a simple arrangement of rubber donuts that offers significantly less damping than the stock setup.
Because the process results...
Because the process results in a stronger material, forged wheels generally have numerous, thin spokes. Whereas cast wheels have unmachined portions, these forged items are completely machined to specification. Note the small bolt-on hub used to adapt the common forging to a variety of disc patterns.
Cast wheels generally have...
Cast wheels generally have a limited number of large, hollow spokes. Note the portion of the rim that must be machined smooth.
Carbon-fiber wheels still...
Carbon-fiber wheels still need to have metal parts in the structure, and these must be bolted or glued--or both--in place.