General aspects of 11- and 12 speed configurations

Starting the consideration from the cassette which I used for many years the 10 speed 12-23. I preferred this configuration over the 11-23 taking the disadvantage on our long descents into account not be able to go into the lead in a Belgium circle, but having the 18 reducing the gear ratio increment between the 17 and 19. This is always important to me in headwind  in the big chainring or for the climbing.   All my discussions with pro riders and technical directors of pro teams came to the same conclusion that the 18 teether is highly appreciated if the race course is hilly. 

START  12-23   12 13 14 15 16 17 18 19 21 23

Subsequently I decided to add now to the ideal 12-23 the 11 teeth sprocket. 

11 speed 11-23   11 12 13 14 15 16 17 18 19 21 23 

The second alternative if a lower gear ratio is of advantage to skip the 18 and add a 25 or 26 and/or scarifying the 11 and add a 27 or 29 

11 speed 11-25(26)   11 12 13 14 15 16 17 19 21 23 25(26)

11 speed 11-27(29)        12 13 14 15 16 17 19 21 23 25(26)  27(29)

With this 3 configurations a wide range of needs can be covered. For special purposes like flat TT and up-hill TT  other configurations like 

11 speed 11-21         11 12 13 14 15 16 17 18 19 20 21  or

smaller increments on bigger sprockets for up-hill TT are more ideal to adjust riders cadence to the given output power and combined resistance (drag and potential energy) by skipping the11, 12 or even the 13.

Now what's ideal for 12 speed ? Again starting with the ideal 11 speed 11-23 it makes only sense to add a 25.

12 speed 11-25   11 12 13 14 15 16 17 18 19 21 23 25

or again if lower gear ratios are required skip the 18 and add a 27 .

12 speed 11- 27(28)   11 12 13 14 15 16 17 19 21 23 25 27(28)

Depending on riders preference if the 11 is really required or of any advantage the 

12 speed 12- 27(28)   12 13 14 15 16 17 18 19 21 23 25 27(28)

evolves and the 18 is back. 

Bottom line is the 11 speed covers a wide range of needs. The 12 speed configuration is ideal if a lot of climbing has to be done e.g. alpine stages with steep grades and long descents.

12-speed Campy 11-27 cassette