Tiagra is the first real groupset in Shimano’s road range, it’s the last stop for trickle-down updates as they move from Dura-Ace to Ultegra to 105. The group just received some of those improvements and there’s some pretty cool stuff coming down the line.
First off, cyclists wanting to run hydraulic disc brakes alongside a Tiagra groupset will no longer have to turn to non-series ST-RS405 dual control shifter/brake units. The new Tiagra brake/shift levers mimic the slimmed down profile of the higher end groups and the guts of the shifting mechanism within have also been upgraded from the non-series levers to provide quicker shifting. Tiagra now allows riders to shift quickly through a cassette with a single lever throw.
Tiagra dual control levers also now come with the option of a short reach lever and more outboard profile for riders with smaller hands, a much needed feature from the 105 and Ultegra lines.
Gearing is improved as well. A lower 48-34T front chainring combination comes on the new Tiagra FC-4700 2-piece crankset alongside 52-36T and 50-34T options. The smaller ration should suit a lot more riders as the gap to between the big and small ring has been brought down to 14T which should cut down on rear cassette shifts.
Finally, a new 12mm E-THRU hubset for disc brakes now appears at the Tiagra groupset level. This 10 or 11-speed hubset is available for 28H or 32H rims and comes with a disc brake-specific O.L.D. of 110 and 142mm respectively.
The new, updated Tiagra 4700 will be available in June 2019.