Shimano

Dura-Ace Di2 ST-7970 STI Shifters

For all the chatter about electronic shifting replacing mechanical, the place where people will love it or hate it is at the shift lever. Shimano rightly lavished plenty of attention when they designed the Dura-Ace Di2 STI Shifters.

In order for the Di2 levers to work at shifting your bike, they must be used in conjunction with the Di2 front derailleur, rear derailleur, battery pack, and wiring kit.

The most obvious advantage to going electronic is the fact that the cable routing doesn't add friction to the system. No cables = no friction. Add to that the system is fast. Really fast. Faster than downtube shifting. 30% faster than shifting on mechanical Shimano Dura-Ace 7900. Better still, the shifting feel is much lighter. You can do it when you're tired. You can do it with "weak" fingers. You don't have to move your wrists or forearm.

Unlike mechanical Dura-Ace, the Di2 shift lever blade doesn't move inward. Instead there are two paddles behind the unidirectional carbon-fiber lever blade. The one closer to the handlebar still does the traditional shifting with the spring (aka onto smaller cogs in the rear, onto bigger in the front), and the one further does the traditional shifting against the spring (aka onto taller cogs in back onto smaller in front). They each have 2mm of travel. Each push results in one shift. Though if you're coasting, you can "pre-shift" any number of gears, and the system will take up the shifting when you start pedaling.

Shimano refined their STI lever when going electric. The levers are slimmer, closer to pre-STI levers, with some more ergonomic refining. Shimano shaved down their profile because they don't need to allow for derailleur cable routing and the internal hardware it takes to precisely shift cable. The shift positions should still closely mimic mechanical Dura-Ace. The lever body, which they refer to as the "perch" has been better shaped for greater long-distance comfort. In addition, the pivot on the lever has been moved for even better modulation.

They did think about weight savings. The levers are 155g lighter. This isn't an insignificant savings. Not only are all the shifting mechanisms rendered unnecessary and left off, but there is a titanium clamp and fixing bolt on each lever to further reduces weight.

The Di2 STI levers come as a set of two levers. No brake cables, brake housing, or wires are included.

A second, or possibly third, set of shifters can be set up on the same system. SW-7971 is the kit that has extra shifting elements that can be placed on aero bars or elsewhere. A Shimano Flight Deck computer (SC-7900) can be attached to the system via the harness. The reach of the levers can be adjusted individually.