MAKING THE BEST POSSIBLE BIKE FRAME CHOICE
Frame Stiffness
Stiffness is an over-used and misunderstood term. Properly used, stiffness expresses a bike frame’s ability to resist forces (stresses) applied against it. In use, forces are continually being applied against a bike frame, whether just from the weight of the rider (load), or from the stress a rider applies to a frame in the form of kinetic energy---especially during aggressive riding behavior like climbing, sprinting, cornering, and accelerating.
Vertical stresses (stresses from loads in the direction of gravity), lateral stresses (stresses resulting from load in a lateral direction) and torsional stresses (stresses resulting from twisting actions) are applied to the bike due to several factors: rider’s weight, height, strength, requirements and geography at any given moment. Note that these dynamic factors are constantly changing due to speed and gravity. So, a cyclist accelerating hard from a stand still, standing up to sprint, cornering at high speed, or climbing a steep grade will generate an enormous amount of vertical, lateral and torsional stress on a frame.
A frame’s ability to properly resist forces applied against it is one characteristic of a great frame, and a frame is appropriately stiff as it resists these forces. We say “appropriately stiff” because a great frame cannot be so stiff that the kinetic energy put into it by its rider is prevented from setting the bicycle into motion. In other words, a frame cannot be stiff as cement, but neither can it be as flexible as cardboard. The best frame manufacturers realize that there is a fine line between making a bike which is stiff enough to withstand the lateral and torsional stresses which are generated against it and the ability for a rider to effectively and efficiently ride. In short, the best frame manufacturers realize that a frame must be “dynamic,” or “reactive,” qualities which ensure that the frame responds to the energy put into it by its rider.
When a frame is overly resistant (too stiff) to forces applied against it, the frame is referred to as “dead.” A dead frame saps energy from its rider, causing them to fatigue quickly and not ride to their full muscular or aerobic potential. On the other hand, a frame that is overly susceptible to forces applied against it is called “soft” or “whippy.” This means that the frame is not strong enough to bear up to the stresses applied against it. In this case, the frame fatigues, leading to inefficient transfer of human power and resulting in the quick degeneration of the bike’s structural integrity.
How Stiff Should My Bike Be?
This is not an altogether easy question to answer and discussing this with a frame expert is ideal, but we can get a good approximation by answering a few questions:
1. How much do you weigh?
2. How tall are you?
3. How long do you like to ride?
4. What are your riding objectives?
How you answer these questions will directly influence how stiff your bike should be. As a general rule, heavier riders should look for stiffer bikes. While “heavier” is a relative term, we tend to think of riders in excess of 185 pounds as heavier. Heavier does not necessarily mean “over weight;” many heavier riders are either tall, or muscular, and it’s a function of their size that translates to an increase in weight. A stiffer bike will be able to withstand the forces a heavier rider will generate, both in terms of vertical and lateral stresses, but also in terms of torsional stresses derived from a larger rider’s greater explosive power.
Taller riders (in excess of 6’0”) will also generate greater stress on a frame from, at least, a lateral stress perspective. The reason for this is that the tubes used in the construction of a larger frame must be longer; to withstand the fulcrum effect, increasingly elongated tube sections must be reinforced, i.e., made stiffer. This can be done in various ways, e.g., butting the tubes, shaping the tubes, or reinforcing them with additional carbon.
If you prefer to do longer rides, especially more relaxed rides, there’s no need to run out and purchase the stiffest race frame available. Depending on your size and height, a frame that is too stiff will require a greater amount of energy expenditure from its rider; conversely, a frame that is too soft will inefficiently transfer energy (specifically, power measured in Watts) from the rider to the frame. This, too, will cause the rider to fatigue more rapidly. As each rider has a limited amount of energy for any given ride, how that energy is consumed via transference into the bike frame is a critical factor in pacing, recovery, and efficiency.
Lastly, ask yourself what your riding objectives are. Are you a racer doing shorter events or longer road races? Are you a time trialist? Are you a triathlete, and if so, what distance events do you typically compete in? Or, are you a recreational rider who enjoys great performance? The answers to these questions will have a significant bearing on not only how stiff your bike frame should be, but even from what materials your frame should be manufactured.
Taking into account your answers to all of the above questions will bear directly on how you should choose your frame. Weight and height, while important factors, cannot alone determine how stiff your frame should be. And, contrary to popular opinion, determining what kind of rider you are cannot alone determine how stiff your frame should. Granted, racers may want “stiff” frames, but stiff is relative to the individual, and how stiff depends on multifarious factors, including what types of events one races.
A great bike is one which balances and effectively utilizes the stiffness of the medium from which it is made (steel, aluminum, titanium, carbon, or some combination of these) with the power generated by its rider. These media, combined with tube diameters, tube shaping, additional properties in the alloys or additives to the carbon composite, are brought together in world class framesets to deliver optimized stiffness and flexibility to work in harmony with human anatomy.
Previous Page
|
Next Page