Be-All, End-All? Dura-Ace Di2 Disc

Be-All, End-All? Dura-Ace Di2 Disc

When I first tried the latest iteration of Dura-Ace in its mechanical form, my first comment was, “You have got to be kidding.” the shift action was so light, the brake power so good for a rim caliper that my reaction was borderline disbelief. This is not the first time I’ve reacted this way to a new Dura-Ace group. That’s how I’ve reacted to nearly every iteration of that group ever since they introduced STI.

I’ve spent the last year (more, actually) riding both the mechanical group (9100) on a road bike and the Di2 version with hydraulic disc brakes (9170) on a gravel bike. They are not the same thing, and while they could be used on reasonably similar bikes, my decision to put the mechanical group on a road bike and the disc group on a gravel bike reflect how I think many people will look at using the two groups. This is an apples and bananas comparison, to be sure, and while this isn’t a shootout, I think considering one relative to the other is warranted.

Let’s get a couple of basics out of the way. Shimano claims the 9100 group weighs 2007 grams without cables. The 9170 group weighs more, but not by tons; 2389g. All but about 40g of the uptick in weight is for the hydraulic discs. The difference in price, though, is significant. The 9100 group has a suggested retail of $2029, which works out to roughly $1/g. The 9170 group merits a more than 50 percent jump in price at $3137. Most of that price jump is for the electronic shifting.

Selecting one group versus the other isn’t easy, but there are reasons to choose each.

The big stop
The more I think about the differences between these two groups the more I think what divides them is imagination. I know, that sounds like crazy talk. Hear me out. The Dura-Ace 9100 group is the ne plus ultra, the finest achievement in traditional road groups thus far on planet Earth. The brakes are incredibly powerful and offer fine modulation. The rear shifting is lighter than the mood at a Grateful Dead concert and the front shifting is lighter than the rear shifting on some previous Dura-Ace groups. Just think about that.

So why would anyone need to top that? That’s where imagination comes in.

Someone asked themselves what it would be like to have a bike with hydraulic disc brakes and shifting that required less effort than it takes to wake up a smart phone. And, sure, there are road bikes out there with this group—why, I can’t fathom—but this group makes most sense on a gravel bike.

Shimano’s electronic shifting is so flawless diamonds turn to emeralds with envy. I’ve never had a single shift that didn’t do exactly what is supposed to happen, plus each shift is faster than I can manage with my bare hands. On the road, it’s interesting, a neat curiosity. But off road where rocks fly up and bikes bounce around and chains bounce, I’ve had mechanical shifts go wrong in more different ways than I can count. I had a derailleur completely self-destruct when I wasn’t doing anything weirder than riding over undulations of a dirt road. So having a shifting system that is instantaneous and as buttoned up as Cary Grant, well that means something. Any time you can simultaneously improve performance and reliability you have a real selling point.

When I rode this group at Dirty Kanza’s Half Pint (only 100—which is the only time you’ll see the word “only” appear before “100”), the nature of perfection is such that I stopped thinking about shifting. I simply hit a button when necessary. I didn’t think about my cadence, about how much force was on the pedals, about whether I was cross-chained or not.

I may ride for a month and not ask as much of a group as I did during that one ride. There were times that as I crested a hill, I’d stand up and hit the two big buttons, upshifting the front derailleur and downshifting the rear derailleur. With Di2, I don’t worry that the chain might get caught or dropped or anything untoward.

I can recall in times past that with many groups the rear derailleur shifted better with the 12-21 than it did with the 12-27. Those bigger jumps, particularly any three-tooth jump, gave some rear derailleurs real trouble. I’ve been riding this group with Dura-Ace’s broadest cassette, the 11-30. If the rear derailleur was ever going to balk at a shift, that would be the cassette.

I expected the front derailleur to shift flawlessly with a Shimano crank; in my case the 50/34 compact. But what of aftermarket cranks? I’ve ridden the bike for most of this season with Praxis’ new 48/32 subcompact crank and the shifting has been just as irreproachable. That may say more about how hard the folks at Praxis work to make sure their chainrings shift as well as anything else on the market, though.

These levers allow for both reach adjustment and free-stroke adjustment. The free stroke adjustment is important for anyone who wants to be able to put their fingertips on the brake levers without immediately causing the brake pads to touch.

After years of innovation and improvement, the road bike market has struggled to keep remaking itself in ways that compel riders to sell a good bike in favor of buying a better one. Working against riders who may contemplate an upgrade to disc brakes on a new bike is the simple fact that all their spare wheels suddenly become useless. While I can see re-lacing Zipp or Enve rims to new hubs, with most wheels it simply doesn’t make sense. So riders are faced with having a bike with a single set of wheels.

What makes the upgrade much more compelling is when you begin to think about how a new bike would allow you to go new places, or places you never went on your road bike. Once you have the rim caliper out of the way, the frame becomes the only limitation to how big a tire you can run.

When I first rode Shimano’s disc brakes on a group ride, I frightened people by over-braking in the peloton. It took a little while to get a feel for the light touch necessary for scrubbing speed. At one point I wondered if Shimano had changed their pad compound to make it easier to scrub speed, but no, it was just a shift in my muscle memory.

Shimano prefer to see bikes running 140mm rotors with this group. After my experience with SRAM and 160mm rotors, I will admit I was concerned about whether I’d have enough braking power with a 20mm smaller rotor. I wasn’t much concerned with how I’d do at Dirty Kanza considering none of the descents are all that long, but on my first ride on dirt roads here in Sonoma County, I did worry.

It was needless. In switching from a bike with a SRAM group and 160mm rotors to Dura-Ace with 140mm rotors the difference I notice is that it is easier to feather the Dura-Ace brake, and the modulation curve flattens out a bit, but ultimate stopping power is indistinguishable between the two systems.

Of the many body and hood shapes Shimano has created over the years, I can say the shape of the 9170 lever body and hood is my new favorite. I’ve liked almost all of Shimano’s levers over the years, with only one real miss in the many iterations of Dura-Ace and Ultegra. The advent of hydraulic reservoirs in lever bodies made most levers bigger, which is a problem for anyone with small hands. While I haven’t taken a tape measure to all the options out there, my hands tell me that the Dura-Ace 9170 lever body is the smallest of the various hydraulic control levers. Part of this can be credited to the fact that the electronics for the shifter take up less space than the cable ratchet. Lever bodies, after all, aren’t like the Pylons in the Land of the Lost, which were bigger on the inside than they were on the outside.

Too bad M.C. Escher wasn’t an industrial designer.

Shimano also took to heart the criticism that the shifters need an obvious click to tell you you had depressed the button enough to execute a shift. It’s strange that such feedback should be so critical, but the rear shifting is so quiet that the combination of a slight downturn in grade and an upshift could leave you wondering whether or not the derailleur had shifted. The mechanism that provides the audible click also communicates the feel of that click through the button itself so that you feel it as much as hear it. I suspect there are times when I only felt it and though I heard it. It makes me think of Rod McKuen’s “Listen to the Warm.” Dreck writing, but you get the point.

The buttons are still relatively small and while the bigger button closer to the brake lever (Shimano calls this the X switch) is textured with small dimples like a golf ball, which makes it easy to distinguish from the smaller button in the rear (Shimano calls this the Y switch) which is smooth as only molded plastic can be, their relatively small dimensions make shifting with thick gloves as hit or miss as trying to sign your name with those gloves on. Because I like to wear long-finger gloves on most of my gravel rides (blame cyclocross), I have to be careful just which gloves I choose in order to have sufficient sensitivity.

Shimano has run the gamut on hood texture, from so overly textured my hands felt overstimulated to completely smooth and slick to the touch of a sweaty hand. These strike the perfect balance of easy grip.

One other terrific chance that Shimano made from the original Di2 group is the elimination of the junction box secured to the stem with an overwrought rubber band. The water bottle batter holder had already been replaced by the seatpost battery bracket, so eliminating the junction box was the remaining task to make a Di2 group as clean in appearance as a mechanical group. The control switch and charging port are now found in a bar-end cap, though that location doesn’t permit you to tuck the tape into the bar end.

Shimano’s didn’t just stop with the obvious stuff. If you go for their PRO bar and stem, the Di2 wires can be routed internally through the bar and out the stem, making for a very clean appearance. That said, the stem is strictly -6 degrees as the hole for wire’s exit is on the underside of the stem (in the -6 position) and there is only the one opening.

Near the opening of this review I mentioned imagination and just how critical it was to creating a group that is this impressive. The fact that this group goes for roughly $3200 (online shopping notwithstanding) makes its creation no less impressive. Here’s the funny thing: I don’t know how they top this. Adding a 12th cog would be cool, but that’s not enough to top what this group has achieved, and when adding another cog won’t change your opinion of a group, that’s when you know it really is superlative.

Final thought: This group is flowers on a spring morning—an eruption of amazing so perfect it causes you to catch your breath.


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  1. Neil Winkelmann

    I’m running the D/A mechanical groupset on my gravel/commuter bike. It’ mostly great and shifts are flawless, but:

    1) Disc brake pad life is very short, even with sintered pads for the hilly, wet riding I do
    2) Rotor noise due to bits of grit/sticks/leaves getting stuck in the calipers from wet roads is annoying. Worse with the solid ice-tech rotors, but better with fenders. I can live with it, but would prefer more clearance, even at the expense of higher lever forces
    3) Squeal in the wet is embarrassing until they heat up and dry out
    4) Lever-travel is longer than I’d like
    5) In the dry, they are plenty powerful, but actually less-so than the 6 year-old Super Record brakes on my summer bike (PED black rims from Fulcrum). In the wet, the discs win hands-down
    6) I like the light feel of the big shift/brake levers for downshifting at the back and upshifting at the front. Small levers work fine, but I actually prefer the Campagnolo buttons for the opposite shifts
    7) Lever bodies feel enormous and clumsy. I much prefer the shape and size of the Campagnolo bodies. I too, have large hands.
    8) I’ve switched to a 105 crankset for winter commuting, having worn out a $et of Dura-ace chainring$ in one winter. The whole 105 crankset (including rings) was half the price of a $ingle $et of ring$ for the DA crank$et.

  2. Patrick

    Great write up. I think the original 685/785 di2 hydro levers are definitely love or hate. For me, it was the first time my XL hands were truly happy on a bike. I almost grabbed 685 levers for a SS build, but the price and shape of the TRP Hylex was very good.

  3. Aar

    Thanks for your comments on applicability of 9170 for gravel and 9100 for road. I also appreciate the comments about roadies having an installed base of rim brake wheels. I migrated from Campy to Shimano on both of my road bikes this year. The Di2 vs mechanical debate was challenging and discussed with many. I chose mechanical. The greatest factors were simplicity and universality but weight was more relevant than I would ever be proud to admit. While still missing the wonderful Campy feel and trying to get front derailleur trim to function identically between bikes, shifting effort and function is a non-issue on mechanical and I don’t regret skipping Di2 despite my LBS owner pointing out its advantages given the opportunity. For my use case, 9170 would be appropriate if I ever pick up an aero bike on which internal cable routing is a thing (cable housing bend radius will never match that of wires or hoses). Again, thank you for openly sharing your opinion of where 9100 and 9170 fit best.

  4. Ron

    Although Dura Ace remains an impeccable if predictable choice, after riding the new Campy 12 speed stuff that is what is going on my bike. I just love the feel of those shifters and brakes; nothing else like it.

  5. George Kirschbaum Jr

    As long as I can afford it on a bike, I will go Di2 and never look back. Ultegra or Durace. Touch->shifted, it’s that simple. The price is the only deal breaker. As for Durace, I wish they’d allow for a larger cogset for the gravel set, but Ultegra is cheaper and really just as smooth… and will take the larger stuff when needed.

  6. Fuzz

    One mystery to me is why Dura-Ace mechanical even exists anymore. For that kind of money, why wouldn’t everyone opt for flawless shifting every time. And with Di2, there is the option to break out of the mechanical box and reprogram the levers to something that feels more intuitive. Add in synchro shifting, and mechanical shifting just feels like buying a really, really good VCR, in lieu of streaming 4k HD.

    1. Author

      It’s a question once can’t help but ask. Your comparison of a good VCR to 4k HD is a really evocative one. Fortunately, the difference between Dura-Ace Di2 and mechanical isn’t as bad as that. And the answer as to why mechanical even exists anymore can be summed up with this one question: “Oh hey, would you like to save a grand?”

  7. Fuzz

    I am mystified as to why Dura Ace and Ultegra mechanical even exists. For that kind of money, who wouldn’t opt for flawless shifting every time, with zero maintenance. Add in synchro shifting and the ability to reprogram the levers to something that makes more sense (breaking out of the mechanical box we’ve been trapped in), and mechanical shifting really feels like putting window cranks on a Tesla.

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