Shimano 105, the component giant's renowned third-tier road group, is undergoing possibly its greatest revamp yet, switching from mechanical to electronic and adding a 12th cog to the cassette for good measure.
Shimano 105 Offers The Biggest Revamp to Electric Technology
The 105 has long symbolized superb shifting performance at a low price, with technology trickling down from Dura-Ace and Ultegra. Electronic shifting technology has finally come down in price enough to be offered in Shimano's core value-performance combination of a groupset as Di2, Shimano's flagship technology of the twenty-first century, reaches its adolescent years.
This newest electronic iteration of the group has long been anticipated, especially since SRAM just made the switch to electronic for its Rival 12-speed group a little more than a year ago. As with mechanical 11-speed shifting, the 105 looks and performs very similarly to its Ultegra and Dura-Ace siblings, benefiting from a strong dose of trickle-down engineering, although with lower-cost components and an associated weight penalty.
105 Di2 - formally known as 105 R7100 - includes semi-wireless shifting, where the shifters connect wirelessly with a single central battery that is hooked into the derailleurs, as with the two more costly groups that were upgraded last year. It's a method that just requires charging one battery, often stored in the seatpost, via a wire that feeds into the rear derailleur, rather than charging each derailleur battery individually, as with SRAM eTap.
More Features Available on the Shimano 105, Other Sets
Because the same Di2 battery has been taken from Ultegra and Dura-Ace for 105, battery longevity, which has always been a key selling point of Di2, should be comparable.
One difference between the 12-speed Dura-Ace and Ultegra is shift speed. Shimano claims that it is somewhat slower on 105 Di2, but still equivalent to the very fast 11-speed Dura-Ace Di2 group. One of the reasons is that the Hyperglide chain was used rather than the current Hyperglide+ chain.
Because 105 is aimed at a higher entry-level or enthusiast-level user, the gear ratios offered in the group cover a broader range and include superior climbing gears. Cassette options include 11-34T and 11-36T, and the crankset will be 50/34T at launch, with a 52/36T option coming later. That means a climbing gear ratio of less than one to one is conceivable. In instance, Ultegra offers an 11-30T cassette in addition to an 11-34T, while Dura-Ace offers both in addition to an 11-28T cassette.
Ultegra and Dura-Ace both have the same two crankset options as the 105, with Dura-Ace also having a 54/40T option. The cranks come in sizes of 160mm, 165mm, 170mm, 172.5mm, and 175mm. Shimano has kept the lowest cog at 11 teeth, like with the 12-speed Dura-Ace and Ultegra. SRAM has shifted to a 10-tooth cog, and Campagnolo has even gone to a nine-tooth cog for its Ekar group, giving both groups a larger sprint gear, which means the chainrings may drop proportionally while still providing a wide gear ratio for sprints and descents. However, shrinking the cog has several downsides.
Part of the rationale for not decreasing the sprint gear is the increased efficiency of a larger cog, which is also why aftermarket derailleur pulley wheels are so massive. However, sticking with 11 teeth has the extra benefit of backward compatibility with earlier freehubs, which means your present wheels will operate well with the new group.
In terms of interoperability, the 105 Di2 may be utilized with 12-speed Ultegra and Dura-Ace components, with certain limitations regarding derailleur compatibility. The 105 11-36T cassette is incompatible with the shorter rear derailleur cages of Ultegra and Dura-Ace, and the 105 Di2 front derailleur has a max chainring size of 52, therefore 54-40T Dura-Ace chainrings would not fit.
While most people would prefer the 105 for its shifting performance, the Di2 version has also received significant braking improvements. Better stopping has been one of the driving motivations for the transition to disc brakes in recent years, and Shimano claims it has improved its already superb hydraulic braking by taking technology from the newest Dura-Ace and Ultegra groups.
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