自行车链条线设计参数.doc

自行车链条线设计参数
Chainline
This refers to how straight the chain runs between the front and rear sprockets. Ideally, both sprockets should be in the same plane, so that there is no sideward motion or stress to the chain. This constitutes "perfect chainline".
In the case of derailer geared bicycles, the chainline is not perfect in most gears. The worse the chainline, the worse the mechanical efficienty of the drive train.
"Correct" chainline for a derailer system is a matter of opinion, and depends on the intended use of the bicycle. There are two "simple" answers to the question of what constitutes proper chainline:
1. One view is that the middle of the cluster should line up with the
middle chainring (or half-way between the two, in the case of a
double.
2. From the parts manufacturers' point of view, the chainline depends
on the diameter of the seat tube where the front derailer mounts.
For fatter seat tubes where the front derailer is farther to the
right, derailer manufacturers want the chainline to be farther
to the right also, because their main priority is shifting
performance, and their front derailers have an optimal chainline
with respect to the edge of the seat tube. This is particularly
a concern in the case of bicycles with indexed front shifting.
From the rider's point of view, chainline is partly dependent on how you are going to use your gears. For instance, consider a road triple vs a mountainbike triple:
, With a road triple, you mostly use the two bigger rings, the granny
is only occasionally used, and only with the larger rear sprockets.
For a road triple, having the cranks close-in is good, because
it increases the usability of the big ring.
, With a mountain bike, the small ring is used much more often, and
must often be used with fairly small sprockets to avoid having
to shift the front under load. For mountain bikes, a more outboard
chainwheel position is often preferable.
Chainline Standards: