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Required capacity = (big ring − small ring) + (big cog − small cog). Your derailleur's rated total capacity must be at or above this number.
Max sprocket is a separate hard limit — the derailleur arm must physically reach your biggest cog regardless of the capacity figure.
Marginal means within 3T of the limit. May shift fine with B-screw adjustment, but you're outside the manufacturer's guaranteed range.
1× drivetrains have no front chainring difference, so required capacity equals cassette range only.
SS (short cage) — lighter, stiffer. For compact doubles (50/34) with tight cassettes (11–28T). Lower total capacity.
GS (medium cage) — standard for most road and gravel. Handles typical 2× setups and moderately wide cassettes to ~36T.
SGS / long cage — MTB and touring. Required for large cassettes (40T+).