Chapter 3: inspection, adjustment, and lubrication
This page explains what is meant by the terms "stress" and "fatigue" as used in this manual.
"Fatigue" refers to a low-stress force, and also refers to the result of repeating that force. "Low-stress force" means a single application of stress that is not sufficient to deform or break the part.
When a low-stress force is repeated many times (a large number of cycles), it can cause a material to become weak or break. Fatigue stress is summative—each cycle, or application, of force is in addition to the last one—so fatigue stress builds up with use over time. Because fatigue stress adds up over time, the larger the forces seen by the part, the shorter the life of that part. If a part has previous damage from fatigue stress, it will be weakened and therefore much less resistant to overload.
"Overload" is a single, high-force load that exceeds the strength of the bicycle frame, fork, or part. When a load exceeds the strength of a structure, the structure will be damaged: deformed, bent, or broken.
As an example, running into an immovable object—even at speeds under 15 miles per hour (20 kph)—can result in an overload. After such an impact, the frame or part will probably be bent or completely broken (separation of the material). However, the results of an overload can be more subtle, appearing more like the damage from fatigue. In addition, with both fatigue stress and overload stress, carbon fiber parts behave differently than do metal parts.
After any high force load, thoroughly inspect all the parts of your bicycle. High force loads include crashes, but you don't have to crash to put a high force load on your bicycle. For example, hitting a large hole in the road or a sharp bump such as a railroad track can put large forces on your bicycle.
The life span of a part varies according to its design, materials, use, and maintenance. Although lighter frames or parts may, in some cases, have a longer life span than heavier ones, it should be expected that light weight, high performance bicycles and parts require better care and more frequent inspections.
Even if you perform regular inspections, if you exceed the limit of strength of your bicycle or a given part, it will break. The Limited Lifetime warranty offered with your bicycle does not mean that your bicycle cannot break; it only means the bicycle is subject to the terms of the warranty.
The most significant variable in durability is the manner in which you ride. This will determine whether your bicycle and its parts will last your lifetime. If you ride hard or aggressively, you should replace the bicycle and/or its parts more often than riders who ride smoothly or cautiously. There are many variables to this equation: weight, speed, technique, terrain, maintenance, riding environment (humidity, salinity, temperature, etc.), and the frame or part itself- so it is impossible to give a precise timetable for replacement. As a rule, it is better to err on the safe side and replace the bicycle or parts more frequently. If you aren't sure, ask your dealer.
Regularly inspect your entire bicycle for signs of stress:
· Dents
· Cracks
· Scratches
· Deformation
· Discoloration
· Unusual noises
If any part shows signs of stress, damage, or fatigue, replace the part before riding the bicycle. Make sure any replacement parts are compatible with the rest of the bike; use the same part or consult your dealer.
When replacing a part, always replace the entire structure. For example, if the fork was impacted, some of the impact was inevitably passed to the frame—so you should replace the entire frameset. When you replace a frame or a part, don't pass the problem to someone else; destroy it.
If your bicycle has a frame, fork, or any parts made of carbon fiber, read the special carbon fiber composite section.