Originally Posted by
Kapusta
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And from what I can tell, the reason you think this is based on a misunderstanding about how chain wrap capacity (which determines cage length) is calculated. Here is how you determine how much chain wrap capacity you need: (Big cog - Little cog) + (Big ring - Little ring)
Your chain capacity argument is OK however, you fail to look at maximum sprocket limitation... short cage tend to be limited with 28t , medium 36t and large is 42 to 52 depending of the model... Hence Sram rival and force long cage being used...
sram medium tend to be limited to 36T max sprocket and 37T
sram medium tend to be limited to 42T max sprocket and 43/45T
so if considering capacity only, on 1x, you should use medium cage with a sram 11-42 cassette (31 capacity) but yet Sram clearly advise to use a long cage et manufacturer are using long cage when above 40T max...
Again, it is not my understanding failing, it is manufacturer specification and advise. And yes, for a given force applied on the bottom pulley, a long cage (mine is ~100mm between axis on my rival long)) will generate more torque to the rotation axles than a short (60mm on my sora short) or medium cage (80mm on my sora medium). So, you need a "better" reaction load for a long cage than a short and medium cage to ensure the same level of tension. Increasing the spring rate is not ideal as the extra load will generate more frictions. So the next best thing is a dampening effect in this instance a clutch...
so ready, you are most likely going against manufacturer advice using a 11-46T with a medium cage... which is probably going to work because manufacturers apply at least 25 to 50% safety factors by "detuning". and again, it may be fine (I do it on my kids bike) but because it works for you, it does not mean it is correct.