Di2 is cycling crack. Do not touch it. Do not take a Di2 equipped bike for a test ride. This will just cost you either your self esteem or $5k.
The problem is, once you have tried Di2, your current really expensive gruppo suddenly becomes wholly inadequate. Once you see what Di2 costs, your really expensive gruppo seems very reasonably priced; but, of course it is, because it is wholly inadequate.
Let's just stick to the sexy bits, shall we, and talk about the shifting. The shifters look mostly like standard DA7900, disguising the fact that you are rolling with the cycling equivalent of hi def porn. The most obvious giveaways are the large bulge on top of the front derailleur and the battery below the bottle cage. The shift buttons require about 7mm of throw (even shorter than Red), about 1/3 of normal shifters, and then the magic happens.
And while this seems like a long conversation, it only takes a microsecond and the derailleurs start moving. Rear shifts feel on par with DA7900. The lever throw is a lot shorter, so the whole shift process is a bit quicker. But once the derailleur is moving, the speed of the shift in the rear is really a matter of the ramps on the cogs, so the shift itself feels the same. Up front, the shifts feel crisper. The shift up to the big ring is especially satisfying. The brain applies just the right amount of pressure, depending on where the rear derailleur is, with a slight overshift and then adjustment back, so that you get a fast shift. I never noticed the shift effort on the front derailleur with my mechanical setups until I started riding Di2. After shifting with a light touch of one finger, mechanical shifting feels like a lot of work and not very precise. Yes, I know that is precious, but I no longer care what luddites think.
Is there any downside, other than cost? Functionally, the only downside is a 60g weight penalty--spit twice before a big climb and you are even there. The battery will last a month for mere mortals. HTC Columbia and other Pro Tour teams are going almost entirely Di2 this year on their bikes, so it has passed the pro peleton sniff test. So far, my only complaint is that the shift buttons are tougher to find with heavy gloves on than a big paddle (and Red is especially good in this regard). Some people complaint about not being able to do multiple shifts in one throw, but I can hit the shifter 3 times in rapid succession just as quickly and get a more precise result than a long throw on a mechanical shifter. Front derailleur adjustment needs to be carefully set to avoid throwing the chain, but that is true of mechanical setups as well. Apart from the very few frames designed for Di2, you have to run the cables with Shimano-supplied tape that is fairly elegant. But, you end up with your downtube shift bosses just hanging out there naked in the wind, with nothing to do. Maybe I will mount some old downtube shift levers on them.
After speccing it on my "race bike", I then declined to race with it for fear I would go down and scuff a $900 derailleur (to be fair, also because crit courses are generally so bumpy that I chose to ride the softer Ti bike). But, last weekend I finally took it out for some laps in anger, and it performed perfectly....much better shift precision than my Red-equipped bike when in serious oxygen deficit. Of course, the circuit was mostly left hand turns, so the derailleurs were safe.
But wait, you say. All this fancy gimmickry is unnecessary. My bike shifts just fine with mechanical shifting. Oh yeah? Does your bike's front derailleur sound like a Star Wars laser cannon when it makes a shift? No? Wholly inadequate. Of course, there is always the risk with Di2 that your bike will become self aware and try to destroy you. That would never happen with Record.
But wait, you say. All this fancy gimmickry is unnecessary. My bike shifts just fine with mechanical shifting. Oh yeah? Does your bike's front derailleur sound like a Star Wars laser cannon when it makes a shift? No? Wholly inadequate. Of course, there is always the risk with Di2 that your bike will become self aware and try to destroy you. That would never happen with Record.
The future is here, my friends. I, for one, welcome new my electronic master. The SRM tells me how hard to pedal, Di2 does all the shifting. The Garmin tells me when to turn. I am now just a happy passenger, a feeble sack of flesh along for the ride. If you are going to go through the effort and expense to spec out high end ride, Di2 should be a consideration.
