Rim Selection

The rim is the backbone of the wheel structure. It connects the rider to the road through the tire, spokes, and hub. Additionally, since the rim is a rotating body, its mass and aerodynamic properties play a significant role in the amount of power required to keep you rolling down the road. The following items should be considered when making your rim selection.

1. Rim Weight: Since the rim is the farthest component from the center of rotation, its mass has the highest effect on inertia. Without getting into mathematical equations, it's important to note that heavier wheels will be harder to accelerate quickly. Some wheels provide weight savings at the expense of strength and stiffness. Be sure to consider your strength, weight and riding style before selecting super lightweight rims.



2. Rim Stiffness: A stiffer wheel will generally transfer power better and allow for higher spoke tension, which significantly improves wheel durability. Stiffer wheels generally feel more responsive and predictable on mountain roads or during criterium races. The trade-off of stiffer wheels is a sacrifice of ride comfort.



3. Rim Aerodynamics: Aerodynamic efficiency is arguably the most important parameter of a road wheel. Its benefits far outweigh mass considerations of a wheel. A good example of this is the solid disc rear wheel used for time trial applications. The mass of a disc can be double that of a spoked wheel and still be a much faster race wheel. During short power sprints around the neighborhood, the disc wheel is often described as slow and flywheel-like; however once the disc is in motion it can reduce aerodynamic drag by over 60%. The important thing to keep in mind is that wheel aerodynamics improve as the rim section gets deeper. The primary trade-off of deep section wheels is their increased sensitivity to crosswinds.
   
   Several manufacturers have balanced the issues of weight, stiffness, and aerodynamics through the use of advanced composite materials. These wheels are generally lighter, stiffer, more aerodynamic and isolate road vibration better then their aluminum counterparts. Keep in mind that there are no "free rides" with any wheel, and in the case of carbon composite rims, they are more expensive and more fragile than standard alloy rims. This should not be a major issue unless you are planning to put thousands of training miles on rims designed specifically for racing. Consider the amount of racing verses training mileage your wheels will be subjected to before making your selection.



4. Spoke Count: Wheels with fewer spokes are generally more aerodynamic. They are also subjected to much higher spoke stress since fewer spokes are required to carry the same dynamic load. Generally higher spoke counts contribute to higher wheel strength and stability. For race wheels, you may want to consider fewer spokes, however there are few benefits to training on wheels with lower spoke counts and typically the result is broken spokes. Consider your body weight, intended wheel purpose, and riding style before deciding on the number of spokes. Also be sure to select rims and hubs with the same number of spoke holes.