You've all seen the electronic shifters on the PRO(tm) bikes...read on...
The excitement over eDA has been noisy, and it's obscured an underappreciated fact: Along with eDA, Shimano is also releasing a new version of non-electronic DA. It'll be known as Dura Ace 7900, and we've finally seen our first confirmed technical details about 7900. The purpose of this posting is to shed some light on what you'll be seeing in the new-for-2009 non-electronic Dura Ace.
STI Levers -
Say farewell to exposed shifter housing. Shimano is making the change to under-the-bar-tape cable routing They refer to it as "integral shift cables". We wonder if Shimano-sponsored pros will find digging deep on the front a but tougher without shift cables to grab on for stability... "Better access to the lever from upper side with closer pivot." Our interpretation of this means that the shape of the brake hood will be different. We've never enjoyed the deep hook of DA brake hoods, and to our ears it sounds like Shimano is modifying the shape to make it more SRAM/Campy-like. In other words, no more plunging hook, and instead you'll see a flatter hood. Beyond the ergonomic improvement, Shimano also claims this leads to smoother braking. You get a reach adjustment mechanism. This is a nice feature of SRAM Red, as well. Folks with small hands should be very pleased. 20% shorter stroke to achieve shift engagement on the right lever. Weight savings thanks to the use of a carbon brake lever and a titanium fixing band & bolt.
Rear Derailleur -
Carbon! The pulley plate will be made from carbon fiber. Shimano is a company built on their commitment to the forging of alloys, so any sort of branching out into composites is a big, big deal. Increased chain wrap capacity. In other words, you can use a wide range of gears (e.g. a 50/34 & an 11/2 without having to resort to a "Triple" rear derailleur. You get an "enhanced pulling cable method" with an audible click when the shift is complete. But the price of superior shifting is this: Dura Ace 7900 STI Levers and the 7900 Rear Derailleur will not be compatible with current 7800-series Dura Ace.
Front Derailleur -
Shimano claims that your days of trimming the front derailleur are over. No trimming will be required. This is a pretty big coup when you compare it to SRAM, since one big upside of Red (in comparison to their Force and Rival gruppos) was its inclusion of FD trim. The FD spring tension has been re-tooled to achieve "featherlight downshifting".
Put aside your sugar-plum visions of a DA Carbon crankset. Rather, Shimano has forged their 7900-series aluminum crank with even thinner walls to make it lighter than any production carbon crankset in the marketplace. When you use the 7900-series crankset with the new 7900-series chain, you'll get no front derailleur rub thanks to its new chainring/spider design. This also allegedly provides improved power transfer, thanks to the superior mating of chain and chainring. More weight savings comes from its new aluminum/carbon composite BB axle. Shimano will also introduce a 7950 version of the crankset, with 50/34 chainrings. This will be the first-ever Dura Ace compact crank (a full, what, 7 years since FSA introduced theirs?)
The 7900 chain is known as the "Super Narrow" chain. The redesigned outer plate resists chain suck, and the new design of both the inner & outer plate mesh with the chainrings with such precision that Shimano claims it reduces mechanical friction by 0.6%. We're a bit unsure how to parse what that 0.6% converts to...Does that mean an extra 2.4w when you're making a 400w effort? We're unsure, and we're eager for a fuller explanation. Perhaps more important is the fact that Shimano also says it's a quieter chain. The 7900-series chain has hollow pins and perforated plates to further reduce weight. Shimano will introduce a "Quick Link" for its 10-speed chains. Our impression is that this means tool-free installation.
Like the chain and the crankset, the cassette sprockets get fine-tuned to optimize shifting, and the cog carrier is a lighter-than-ever aluminum. You'll see a wider array of cassette ratio options. In addition to all of the options you get in 7800, you'll also see an 11/25, 11/27, and an 11/28. Before you laugh at the 11/28, keep in mind that this is SRAM's #1 selling cassette ratio! All the ratios made in the 7800 will be produced as 7900-series models as well.
Brake Calipers -
Dig this: "Enhanced brake arch proportion." We think this means that you get quicker caliper response when you hit your brake lever, and perhaps better stiffness under heavy braking. We suspect that this is a photo of the new brake. Interestingly, the boys over at the Weight Weenies forum pointed out that this poor rider appears to have his brake shoes on the wrong side... Lower profile outer cable stop. This improves cable routing, which decreases drag and improves the snappiness of the lever. If you've ever installed a set of Zero Gravity brakes, you know that fine-tuned brake cable routing is something you should never take for granted. The brake pad compound changes. Shimano claims that the improvement will be most noticeable in the wet, where stopping power improves 210%. In the dry, you should expect a 120% improvement in stopping power. Add'l titanium hardware saves overall weight.
Flight Deck Computer -
It's still integrated into the STI levers, but the functionality gets much broader -- It includes a heart rate monitor, altimeter, and an inclinometer. It's a full-on 2.4GHz wireless system, and you can even download data wirelessly onto your PC.
A final note about backwards compatibility:
Rear Drivetain -- The 7900 system is only compatible with other 7900 components. The 7900 rear derailleur is compatible with 7800-series cassettes, but that's it. There is no other cross-compatibility. This also means that 7800-series components cannot be used in piecemeal with 7900 if your plan is to upgrade one component at a time. More or less, you'll need to upgrade to 7900 STI, rear derailleur, cassette, and chain in one fell swoop.
Front Drivetrain -- Same story. There's an Iron Curtain between 7900 and 7800. The only kinda, sorta compatibility is between the 7900 front derailleur and the 7800 crankset. Shimano states "slower shifting may occur depending on frame dimension" if you choose to mix things like this. We're not sure if "dimension" means frame size or geometry or what. But we can't imagine someone running a full 7800 bike with the exception of a 7900 front derailleur, so it's not something we're terribly worried about.
Brake Systems -- The 7900 STI Levers are compatible with 7800-series brake calipers.
We're looking at a best-case scenario of a late September 2008 delivery timeline. We're sure it'll be all over the '08 Tour de France, and in full force at the Eurobike tradeshow shortly thereafter. But in terms of delivery, if it's before Halloween, we'll be stoked.