From July 2016, Shimano will be offering a new hydraulic disc brake option for its Tiagra groupset. The move is a sure sign of the company’s ongoing faith in road disc brakes, but more significantly, it will bring hydraulic braking into the realm of entry-level road bikes.
Tiagra has long served Shimano’s road catalogue, first appearing in 2001. At that stage, Tiagra 4400 comprised a nine-speed transmission and the same STI technology as Shimano’s higher-priced groupsets.
Since then, the groupset has benefitted from the trickle down of Shimano’s technology, first gaining a ten-speed transmission for 2012 (Tiagra 4600) followed by a four-arm crank design, new lever ergonomics, and shifter cables under the bar tape when it was overhauled last year (Tiagra 4700).
Now Shimano is adding an option for hydraulic disc brakes to the groupset with new dual-control levers (ST-RS405) and flat-mount callipers (BR-RS405). Rather than create a new rotor to complete the set, Tiagra hydraulic disc brakes will make use of Shimano’s existing 140mm and 160mm Ice Tech rotors (SM-RT81-SS/SM-RT81-S).
The ST-RS405 levers are still ten-speed-equipped to match Tiagra 4700 but the new lever now gets Shimano’s Vivid Index technology, just like the 11-speed 105 hydraulic brake lever (ST-RS505) that was released last year. Vivid Index was introduced in 2011 as part of Shimano’s off-road XT groupset and was designed to provide a light shifting action with clear feedback for the user (in the form of a pronounced click that can be felt and heard).
The shape of the new Tiagra lever is distinct from Shimano’s higher-end hydraulic road levers and something of a return to the original STI shape. Every hydraulic road lever requires extra room to house the master cylinder for the brakes; in this instance, it appears as if the shifting mechanism has been re-positioned in front of the lever blade, accounting for the large bulb (or shifter pod) at the end of the hoods.
By contrast, the new BR-RS405 callipers largely resemble Shimano’s other road disc offerings. Interestingly, the company will not be offering a post-mount calliper for this groupset and appears to be devoting all of its new road disc callipers to the flat-mount format that it introduced a couple of years ago.
While it’s unclear whether this decision reflects Shimano’s ambitions for the flat-mount format or demand from manufacturers, I think we can expect post-mounts to disappear from road disc bikes sooner than later.
The new Tiagra brake callipers come equipped with Shimano’s standard resin pads, but they are compatible with the company’s Ice Tech pads. The latter are fitted with cooling fins that help radiate the heat generated during braking into the surrounding air, thus maintaining braking control under more demanding conditions and also preventing pad glazing.
Like all of Shimano’s other hydraulic disc brakes, Tiagra disc brakes will use the company’s proprietary mineral oil with bleed ports positioned in the calliper and the lever to suit Shimano’s simple funnel bleeding strategy. Each lever is equipped with up to 10mm of reach adjustment but as with other Shimano hydraulic road levers, pad contact point is non-adjustable.
With the introduction of ST-RS405 and BR-RS405, Tiagra becomes Shimano’s fourth road disc offering, as shown in the table below:
I think this table serves as a pretty good blueprint for where the development of road disc bikes is headed in the next year or two. Shimano’s road disc technology has rapidly trickled downwards to entry-level groupsets (especially when compared to MTB), so it seems likely that there will be a lot more entry-level road bikes equipped with disc brakes for 2017.
We have already seen the first signs that Shimano is working on the next iteration for its Dura-Ace groupset, including a new flagship version of its road disc brakes – a clear sign that a general migration is underway.