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Tech feature: 2009 Shimano Dura-Ace 7900, June 2, 2008
Shimano releases official details on upcoming new Dura-Ace group
By James Huang
After months of speculation, industry leaks and rumor, Shimano has finally released official technical information on its upcoming Dura-Ace 7900 mechanical group. As it turns out, the majority of the information in our earlier reports has stood up quite well but one question this official release finally answers is what the new componentry will look like.
To sum it up in one word: wow.
Dura-Ace 7900 will adopt an edgier look not unlike the latest generation of XTR. The lines are cut deeper and the two-tone finish is far more eye-catching. The overall appearance is darker and more businesslike, and we can't wait to see it in person.
And as for final technical details? Read on.
Hollow forging technology extends to chainrings
The outgoing Dura-Ace 7800 crankset was already competitive in weight and the industry benchmark for rigidity but Shimano says the new 7900 version is both 50g lighter and a significant 20% stiffer. Total claimed weight is now just 690g including bottom bracket (which is, of course, said to be better sealed and smoother running), putting it within a stone's throw of, or even lighter than, most high-end carbon offerings.
While most of those gains are likely due to the new arm design, a new "100% hollow" outer chainring will also make its own contribution to the 'lighter and stiffer' theme. We're not sure that most recreational riders will be able to feel the difference in chainring rigidity underfoot but particularly strong pro riders who have been known to fold outer rings in the past just by pedaling will assuredly be happy with the improvement. As if it were possible, Shimano also claims that tooth profiles are further refined for even better shifting under power, too.
As we reported earlier, the Dura-Ace badge will also make its way on to a compact offering for the first time. Shimano will offer that version in a single 50/34T gear combination although standard BCD models will be available in 53/42T, 52/39T, 53/39T, 54/42T, 55/42T and 56/44T. Just as before, Dura-Ace cranks will be available in a wide range of lengths from 165-180mm in 2.5mm increments.
Somewhat surprisingly, Shimano will retain the current generation's pinch bolt method of attachment for the non-driveside arm instead of the supposedly stiffer and lighter one-bolt arrangement used in XTR.
Shift options for new Dura-Ace
We don't have much new to add on the new STI levers other than what we've already told you but can at least confirm that our reports on the new body and unidirectional carbon blade shapes, dual cable routing options, adjustable reach and 20 percent shorter lever throws were all spot-on. Shimano also confirmed that the new completely wireless FlightDeck option will finally include long-overdue heart rate monitor and altimeter features as well as downloadable data (sorry, no word on Mac compatibility just yet).
Official weight for the new STI levers is 370g per pair, 50g lighter than last year.
Triathletes and time trialists (and somewhat strangely, luddites) will be happy to hear, though, that Shimano will also include new bar-end and yes, even down tube shifters in the new Dura-Ace range. These were necessitated by 7900's new derailleur cable pull ratio but the inclusion of the down tube shifters is interesting nonetheless (a nod to Lance Armstrong, perhaps?).
In another first for Dura-Ace, there will also be a full-carbon bar-end brake lever.
The matching derailleurs
The Dura-Ace 7900 rear derailleur will boast a wider gear range than before: maximum cog size will be 28T and total capacity (total tooth difference between the two chainrings plus the total tooth difference between the smallest and largest cassette cogs) jumps to 33T. Carbon fiber pulley cage plates and a composite body knuckle help drop the weight down to just 166g. Increased cable pull ratios relative to 7800 should result in more accurate performance and longer service intervals.
The corresponding front derailleur also gets a revised cable pull ratio and spring for a lighter action at the lever. Pivots and links are widened for reduced slop and the cage remains a nickel-plated alloy design. As previously reported, the new cage shape has allowed Shimano to completely eliminate the outer trim position entirely. Claimed weight for the braze-on version is 68g.
While the new cable pull ratios may mean better performance for this newest generation of Dura-Ace componentry, it also unfortunately means that 7900 shifters and derailleurs will not be compatible with earlier versions.
More cassette options and a lighter chain
Shimano will retain the familiar alloy spider and steel-and-titanium cog formula for Dura-Ace 7900 but updated shaping to both supposedly drop some weight and improve shift performance. Things are still 10-speed but gear options have opened up dramatically. Offerings will include 11-21T, 11-23T, 11-25T, 11-27T, 11-28T, 12-23T, 12-25T and 12-27T. Claimed weight for a 11-23T sample is 163g.
The new chain will finally provide an option to the dedicated installation pin in favor of a more user-friendly reusable link (consumers can still use the special pin if they want). Hollow pins and perforated inner plates reduce weight by 20g to 251g. The newly directional design incorporates updated inner and outer link shapes for smoother running and greater contact area which is expected to improve durability.
Stopping on a dime
The new Dura-Ace brake calipers shave almost 30g per pair via aggressive relieving but still claim increased stopping power thanks to the refined shape. New pad compounds are said to double braking friction in wet conditions; dry performance is up 20 percent. In spite of the weight losses, the new calipers will thankfully retain a full complement of features including easily adjustable spring tension and centering.
New hubs are easier to live with
Shimano's continuing use of adjustable angular-contact loose ball bearing systems in its hubs makes perfect sense from an engineering standpoint but the nuances of actually making those adjustments are often lost on general consumers. As such, Shimano will add a new easier-to-use system to the Dura-Ace 7900 hubs that requires but a single hex key; no cone wrenches are required.
Aside from that, the current alloy axle material is expected to be carried over while the titanium freehub body will retain its faster-engaging internals for a more direct feel.
The competition heats up
We can't say with certainty that SRAM's introduction of its premium Red group sparked any sort of technology war but it's perhaps no coincidence that total weight for the new Dura-Ace 7900 is now sub-2000g, 180g lighter than before. With Campagnolo's new groups set to debut shortly here as well, the competition at the top-end of the scale has grown remarkably fierce.
If any of you were holding out for something new (or were just waiting for current generation stuff to go on sale), your time has just about arrived: Dura-Ace 7900 is scheduled to land in stores this fall.
For a thumbnail gallery of these images, click here
Images by Shimano
Images by Benny Devcich