Di2 Details

In my pre-Interbike column in newsletter No. 411 I mentioned a few things I was hoping to see at this year's expo. Among them was a price drop for Shimano's electronic Dura-Ace Di2 components so you don't need to be Donald Trump to enjoy what I think is the most interesting technical development in years.

I got my wish! But there's a catch: The Di2 price cut to $1,799 was a one-time, show-only offer for bike industry people and good for just one kit. Everyone else gets to pay about $3,260 for the electronic parts or almost $5K if you need a whole Dura-Ace Di2 group for building up a frame.

At Interbike I test rode Di2, sat in on a standing-room-only Shimano tech seminar about it, and discussed it with everyone to learn more so I could tell you more.

It's Time

One reason Shimano's battery-powered shifting is intriguing is because other companies have tried and failed. You might remember the Browning front derailleur, Mavic's Zap and Mektronic systems and Campagnolo's now-shelved prototypes. For Shimano to go electric says the biggest player in the industry believes it's time, and that makes me want to pay attention. That, and because I keep running into people who are lusting after it.  

The Di2 kit includes the derailleurs, brake/shift levers, a wire kit, a battery that attaches at the bottom bracket end of the down tube, and a charger. The system's brain is located in the front derailleur's body, which accounts for its larger size. Also offered is a wiring kit that includes button shifters for aero bars. This lets a rider change gears with the regular Di2 levers or when stretched out in an aero position — great for time trialists and triathletes because no change in body position is necessary. That's one of Di2's key advantages. The system is compatible with Shimano's Flight Deck computer.

Smart Parts
 Di2 stands for "digital integrated intelligence." When you press one of the small shift buttons, an electronic signal is sent to a derailleur. It knows exactly how far to move for a perfect shift. Regardless of how much pressure is on the pedals, the worm drive inside each derailleur makes shifts powerfully and precisely.

 

Once Di2 is set up, Shimano says, it should not come out of adjustment. There are no cables or housings to stretch. In the event you do need to fine-tune the shifting, you simply put the system in adjustment mode and press buttons to dial it in.

 

The rear derailleur includes a type of clutch that lets it move inward in a crash, reducing the chance that it and the frame hanger will be damaged. To reset the derailleur's precision, just shift a few times.

 

 

Automatic Trimming

Another intelligent thing Di2 does is trim the front derailleur cage. When the chain's angle changes front to back, the cage moves automatically to prevent rubbing. You always have a quiet drivetrain. This feature also stops the chain from accidentally falling onto the frame during shifts to the small ring.

 

Those front derailleur functions are wonderful, but it's the shifting that really blows me away.

 

The front actually shifts as quickly and cleanly as the rear. The chain will glide onto the teeth even if you're standing and jumping from the 34- to 50-tooth ring. On my test ride at Interbike's Outdoor Demo I couldn't get over this. I kept trying it and never missed a shift. To underscore that this isn't your father's front derailleur, the motor makes an electronic chirp with every shift.

 

 

Button Shifting

It takes a little practice to hit the right buttons on the brake/shift levers. They're shaped like STI shift paddles and are in the same locations, but they're smaller and close enough to each other that I kept tapping the wrong one. I was getting upshifts when I wanted downshifts, and vice versa. I think I'd get over this pretty quickly, given the chance to ride Di2 a while.

 

Eliminating shifting hardware from inside the levers lightens them by 155 grams, makes them narrower for better ergonomics and changes the pivot point for better braking leverage. Reach adjustment is included, as in standard Dura-Ace levers.

 

 

Battery Power

Obviously, Di2 is so new no one can say how it will hold up. It does appear to be well built with heavy-duty wiring, waterproof connectors, a quality lithium-ion battery (easily removed for recharging) and even a tidy installation kit that lets you hide the wires beneath an adhesive channel.

 

Some companies, such as Spain's BH, are already making frames with wire channels beneath the down tube and a pocket to partially enclose the battery. For frames made to accept it, Shimano provides a kit to almost completely hide the wires.

 

As you'd expect, there was lots of curiosity about the battery — the Achilles heel of any electrical device. The Di2 version weighs 71 grams (2.54 oz.) and is only slightly larger than a patch kit. It can be recharged in 90 minutes and power about 1,000 miles (1,610 km) of riding. Shimano's Wayne Stetina, who has been on Di2 longer than anyone, says he routinely gets 1,500 miles (2,415 km) between charges.

 

There's a battery indicator light on the front wire so you know when it's time to recharge. If the battery gets very low, the front derailleur won't work but you'll still be able to shift the rear about 50 times. Should the battery die completely, the chain will stay in the gear it's in, not default to the smallest cog.

 

The battery can be recharged to full capacity 300 times, which means if you charge it weekly per Shimano's recommendation for regular riding it will last nearly 6 years. Replacement batteries currently cost $100. It would take less than a minute to stop and install a backup battery if you chose to carry one.

 

 

Bottom Line

The more I learn about Di2, the more I want it. I had reservations at first, even after my test ride. We've all had battery-powered tools die, and it would be frustrating or worse for shifting to croak on an important ride.

 

Some testers at Interbike said they wished they could hold a button and shift up or down the entire cassette instead of getting only one cog per press. Shimano says this isn't possible and still retain the accurate rock-solid performance of Di2. Besides, shifts are so quick that such a feature really isn't necessary.

 

What I like most is the extraordinary front shifting. But I'm almost as excited about not needing cables and housing, which always stretch, eventually break and require fiddling with adjustments.

 

Then there's the advantage of not having to pull gear cables against derailleur springs. I think that by the end of a race or century ride, Di2's effortless shifting might leave you feeling better with much less tension in the wrists, hands and maybe the upper body. You'll shift more often too, saving your knees as well as your energy.

 

Combined with all the other advantages, Di2 starts to make mechanical Dura-Ace pale in comparison. Too bad everyone can't get an industry discount.

 

To see Di2 in action, check the CompetitiveCyclist.com video at http://tinyurl.com/yeuepcx

(Jim Langley has been a pro mechanic and cycling writer for 37 years. At RBR he's the author of Your Home Bicycle Workshop and moderator of the "Roadie Rap" technical forums on the Premium RBR Site. Check his personal website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim's streak of consecutive cycling days has reached 5,747.)