Originally Posted by
Fentuz
so you wrote a very long reply without having read properly what I said… if you have a longer cage, you get greater torque generated by the chain whip than the same whip on a short cage… so as you mentioned , chain wrapping is important and linked to the tension of the chain. And clutch-less long cage will not ensure the adequate tension on bumpy terrain…
on short and medium cage they are not needed and are not on 2x gravel (2x9 is sora by default) or 3x9 mtb (altus/acera).
long cage is required for 40+T… hence the clutch
I misread you? Were you not saying: Larger cassette cogs on modern MTBS mean you need longer cages.
If so, this is incorrect.
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)
While a larger range cassette requires more chain wrap, so does having multiple rings up front. And fewer rings mean less wrap capacity needed.
This is why my 1x setup 11-46 cassette uses a medium cage length, while a 3x9 with 22/32/44 x 11-32 uses a long cage. That's right, much bigger cassette, less chain wrap needed. Do the math and it makes perfect sense:
For a 3x9 with 22/32/44 rings and 11-32 cassette: (32t - 11t) + (44t - 22t) = 43t
for a 1x11 with a 32t ring and 11-46 cassette: (46t - 11t) + (32t - 32t) = 35t
So when you say that modern mtbs with wider range cassettes need longer cages, you are mistaken. The move to 1x offset the need for additional chain wrap capacity.
The reason low end mtb RDs (like acera and altus) don’t have clutches is because they are low end RDs. Higher end 2x mtb setups DO have clutches (or at least they did while 2x was still a thing).
And as a history lesson, shimano introduced clutches back when the largest cogs they made were 36t.