This invention relates to an improved chain, especially to a chain used on a mountain terrain bicycle.
Typically, a multi geared mountain terrain bicycle has a plurality of sprocket wheels and a gear cluster connected by a chain and controlled by a rear and a front derailleur. The chain is linked by a plurality of links each composed of a pair of inner chain plates, outer chain plates, rollers, and a chain pin. Because of the requirement for strength, a distance between any two inner chain plates is restricted to a certain width. However, a standard sprocket or gear has specifications in thickness. It is noted that the distance between two inner chain plates is larger than a width of the sprocket, and when a tooth of a sprocket is inserted between the inner chain plates, a large gap still remains.
Since the gap allows a lateral movement of the chain against the gear cluster or sprockets, an unfavorable condition results: the sprocket may not be allocated on a central line of the chain, i.e., a biased condition, such as shown in FIG. 8, wherein A and B indicate a central line of a link 80 and a sprocket 90, respectively. When the chain is guided to a desired sprocket by the rear derailleur as a rider is shifting, the derailleur has to move the biased chain a distance before shifting can occur. Further, if the derailleur moves the chain too much to align with the desired sprocket, the chain easily falls onto an adjacent sprocket with a large diameter and then skids down to the desired sprocket. Such an up and down motion of the chain causes damage to the chain itself by a twisting force occurring in the motion. Also, as the rear derailleur is quickly driven, the motion of the chain caused by an misalignment increases loading of the rear derailleur, thereby increasing the possibility of damaging the derailleur. As a result, the expected life of the chain and derailleur are reduced.
When a rider is riding on a sloped rugged area at a high speed, the chain vibrates in a vertical and a horizontal direction. A force caused by vertical vibration is absorbed by guide wheels of the rear derailleur, springs, and the tire. However, since the gap existing between the inner chain plates and the sprocket cooperates with a lateral force produced by a horizontal vibration, the chain engaged with a sprocket is easily disengaged with the sprocket to automatically "jump" to an adjacent sprocket. Since the rear derailleur is not displaced and still remains in an original position, the rear derailleur and the chain are easily damaged by the resulting twisting force. That is very dangerous to the rider.
It is the purpose of this present invention, therefore, to mitigate and/or obviate the abovementioned drawback in the manner set forth in the detailed description of the preferred embodiment.