What is torque?
In simple terms, torque is a twisting force that is likely to cause an item to rotate.Torque is calculated as force multiplied by length with the length being the distance between the rotational axis and the point where the force is applied. Torque is measured most commonly as Newton meter (Nm), pound-inch (lb-in), or pound-foot (lb-ft) units. The last two are common in the U.S. but are often referred to as inch pounds and foot pounds. Newton meters are standard on most bicycle components.
Of the common measurements it is possible to convert between them,
It is commonly believed that bolts and nuts often come loose for no apparent reason. However, the common cause for threaded fasteners loosening is simply lack of tension during initial assembly. Vibration, stress, use, or abuse cannot typically overcome the amount of clamping force in a properly sized and secured threaded fastener.
Torque Device Use,
To achieve correct torque on a bolt or a nut, a torque device should not be handled like a normal wrench or screwdriver. It is calibrated to provide precise torque, which is essential in the assembly process. Whereas a standard wrench might be used as a hammer in a pinch, a torque wrench should never be used for anything other than its intended use. Even dropping the wrench might render its accuracy unsatisfactory.
Most mechanics are guilty of not using a torque wrench at least some of the time and some still disagree, arguing that their years of experience have given them the “feel” needed to properly torque bolts, but test after test has shown this is rarely true
However, bicycles and riding itself have changed considerably in a very short time. With more carbon fibre being used there is simply no way to get a torque specification correct by feel. Over Tightening carbon fibre components for example a seat post will lead to crushing and ultimately failure of the component.