Very efficient! More efficient than a 1x and 2x setup.
Compared to a 1x, less cross chaining is required, sprocket and chainring sizes are larger and thus chain tension, crank and hub bearing losses are lower. Compared to a 2x; the fact that the 0.7 ratio of the hub still uses the large chainring in front, results in 30% less chain tension and thus lower chain, crank and hub bearing losses.
On top of this you will experience that you will use the Classified hub much more frequent than a normal front derailleur, this means that in practice you will have less cross chain losses. The hub does not have any additional losses on in the 1:1 ratio, and is designed to have extremely low losses in the 0.7 ratio which are completely balanced out by the big chainring and straighter chainline by using a Classified setup.
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