Condensed Answer: The Tiagra 4700 series is a 10-speed road groupset from Shimano with special characteristics.
The shifters have a unique cable pull; the derailleurs have the shift ratio of 11-speed road mech.
Consequently, the Tiagra 4700 can be combined with 11-speed derailleurs (including 105) besides the original Tiagra 4700 units.
Modern shifters are indexed. The movement of the rear and front shifters is segregated into clicks depending on the number of gears that the bike has. Each click indicates a shift and is initiated by the shifters by pulling or releasing a pre-determined amount of gear cable.
The advantage of indexed shifters is that the rider only has to pull or press a lever until a click happens without having to guess where to position the shifter.
The amount of pulled or released cable is known as cable pull and depends on the following characteristics:
- Number of gears
- Bike type (road or MTB)
- Manufacturer of the shifter
Rear Shift Ratio
Derailleurs have a shift ratio that determines how much the derailleur moves per 1mm of cable pulled or released by the shifter.
That rear shift ratio in combination with the cable pull pre-determines the position of the derailleur in each gear and ensures fast and accurate shifting.
Just like the cable pull, the shift ratio depends on the number of gears, the bike type, and the producer of the component.
Tiagra 4700 Is Different
As mentioned in the condensed answer, the Tiagra 4700 series has special properties.
First, the cable pull of the shifters matches neither that of 10 or 11-speed models. It’s unique to the Tiagra 4700 series.
Second, the rear shift ratio of Tiagra 4700 rear derailleurs does not match that of 10-speed road derailleurs even though the series is 10-speed.
The rear shift ratio of other 10-speed road Shimano derailleurs is 1.7. Meanwhile, the rear shift ratio of Tiagra 4700 derailleurs is 1.4 and matches that of 11-speed road derailleurs.
Since the rear shift ratio of Tiagra 4700 matches that of 11-speed road derailleurs, it’s possible to integrate an 11-speed road derailleur into a Tiagra 4700 system. That includes Shimano 105 11-speed models.
The derailleur itself does not know or care how many speeds the bike has. The derailleur simply executes commands from the shifter. Thus, the 11-speed derailleurs will work just fine in a 10-speed Tiagra 4700 system.
However, if you want to use an 11-speed derailleur and an 11-speed cassette, the Tiagra 4700 shifters won’t cut it.
As mentioned, the cable pull of Tiagra 4700 shifters is unique to them. Why? The cable pull has to be different because the series is 10-speed but the derailleurs have an 11-speed rear shift ratio.
If the original 10-speed cable pull is kept, the derailleur will not move to the proper location. For that reason, the cable pull of Tiagra 4700 was changed to values that move an 11-speed derailleur to the right cogs on a 10-speed cassette.
What about the front derailleur?
The Tiagra 4700 front shifter has the same pull as other 11-speed series. For that reason, it’s possible to integrate an 11-speed 105 front derailleur in a Tiagra 4700 drivetrain.
What About The Cranks?
Both Tiagra and Shimano 105 use the Hollowtech 2 bottom bracket. Consequently, it’s possible to install 105 cranks on a Tiagra drivetrain.
Listing The Possible Combinations (from the perspective of derailleurs and shifters)
If you want to combine Tiagra 4700 series with 105, the following combinations are viable:
1. Tiagra 4700 shifters + 11-speed 105 derailleurs + a 10-speed cassette
2. 105 11-speed front derailleur + Tiagra 4700 front shifter
3. Tiagra 4700 rear derailleur + 105 11-speed Shifter + 11-speed Cassette