Disc brake component combinations
Unlike rim brakes, disc brake components for road bikes come in several combinations. Basically, they are divided according to whether they are hydraulic or wired, and the STI and brake combination is determined accordingly.
For hydraulic systems, the STI, calipers, and hoses must all be dedicated to hydraulics.
On the other hand, for wire (mechanical) disc brakes, the STI and wires (inner and outer) can be used for rim brakes, and only the caliper brake is dedicated for disc brakes.
Shimano Hydraulic Disc Brake Components
Shimano’s lineup of hydraulic components for road bikes includes four grades: DURA-ACE, ULTEGRA, 105, and TIAGRA.
Shimano STI levers for road and hydraulic disc brakes
STI levers for hydraulic disc brakes in Shimano’s current line are STI levers for TIAGRA and above. In other words, they can only be used with 2x10 and larger components.
Note that although the brake construction is hydraulic, the products differ depending on whether the shifting construction is Di2 (electric) or wire (mechanical).
As of February 2022, only ULTEGRA and above are equipped with Di2. STI levers with “hydraulic x Di2” will have a “70” in the 10th place of the model number, while STI levers with “hydraulic x mechanical shift” will have a “20” in the 10th place of the model number.
Model numbers in parentheses ( ) are for small hand models.
Brake caliper for Shimano road and hydraulic disc brakes
Shimano’s brake calipers for road and hydraulic disc brakes can be used with TIAGRA and higher components to match STI levers. Shimano road-oriented components are also compatible with GRX brake calipers.
Shimano road brakes have the model numbering rule “BR-RXXXX”, but the caliper for disc brakes has a “70” in the tenth place of the model number.
Shimano Mechanical Disc Brake Components
Shimano STI levers for road and mechanical disc brakes
For mechanical disc brakes, the same STI lever is used as for rim brakes. Therefore, the available STI levers are “all but the “hydraulic models” of current road STI levers”, so there is a huge choice, from 2x8 to 2x12.
Note that there are two models of STI levers for mechanical brakes, DURA-ACE and ULTEGRA, depending on whether the shifting is Di2 or wire.
STI levers for “mechanical x Di2” have “50” in the tenths place of the model number, while STI levers for “mechanical x mechanical shift” have “00” in the tenths place of the model number (with some exceptions, such as front 3-speed).
Shimano brake caliper for road and mechanical disc brakes
The disadvantage of Shimano’s brake calipers for disc brakes is that they are mainly hydraulic, so unlike STI levers, the variety is much smaller.
Since there are only the above four types in the current line, if you use mechanical disc brakes, you should consider calipers from other manufacturers.