2009 Shimano Dura-Ace 7900, June 2, 2008

lukehunt · 发表于 2008-6-2 18:45:40

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http://cyclingnews.com/tech.php? ... ano_dura-ace_790008

Shimano releases official details on upcoming new Dura-Ace group
By James Huang

After months of speculation, industry leaks and rumor, Shimano has finally rel
eased 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 answer
s 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 XT
R. 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 s
ee 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 69
0g 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% ho
llow" 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 f
eel 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 w
ill assuredly be happy with the improvement. As if it were possible, Shimano a
lso claims that tooth profiles are further refined for even better shifting un
der power, too.

As we reported earlier, the Dura-Ace badge will also make its way on to a comp
act offering for the first time. Shimano will offer that version in a single 5
0/34T gear combination although standard BCD models will be available in 53/42
T, 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 increment
s.

Somewhat surprisingly, Shimano will retain the current generation's pinch bolt
method of attachment for the non-driveside arm instead of the supposedly stif
fer 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 alre
ady told you but can at least confirm that our reports on the new body and uni
directional carbon blade shapes, dual cable routing options, adjustable reach
and 20 percent shorter lever throws were all spot-on. Shimano also confirmed t
hat the new completely wireless FlightDeck option will finally include long-ov
erdue 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 happ
y to hear, though, that Shimano will also include new bar-end and yes, even do
wn 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: m
aximum cog size will be 28T and total capacity (total tooth difference between
the two chainrings plus the total tooth difference between the smallest and l
argest cassette cogs) jumps to 33T. Carbon fiber pulley cage plates and a comp
osite body knuckle help drop the weight down to just 166g. Increased cable pul
l ratios relative to 7800 should result in more accurate performance and longe
r service intervals.

The corresponding front derailleur also gets a revised cable pull ratio and sp
ring for a lighter action at the lever. Pivots and links are widened for reduc
ed slop and the cage remains a nickel-plated alloy design. As previously repor
ted, 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 ge
neration of Dura-Ace componentry, it also unfortunately means that 7900 shifte
rs 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 formu
la for Dura-Ace 7900 but updated shaping to both supposedly drop some weight a
nd 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 s
pecial pin if they want). Hollow pins and perforated inner plates reduce weigh
t by 20g to 251g. The newly directional design incorporates updated inner and
outer link shapes for smoother running and greater contact area which is expec
ted to improve durability.

Stopping on a dime
The new Dura-Ace brake calipers shave almost 30g per pair via aggressive relie
ving but still claim increased stopping power thanks to the refined shape. New
pad compounds are said to double braking friction in wet conditions; dry perf
ormance is up 20 percent. In spite of the weight losses, the new calipers will
thankfully retain a full complement of features including easily adjustable s
pring tension and centering.

New hubs are easier to live with
Shimano's continuing use of adjustable angular-contact loose ball bearing syst
ems in its hubs makes perfect sense from an engineering standpoint but the nua
nces 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 hub
s 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 ove
r while the titanium freehub body will retain its faster-engaging internals fo
r 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. W
ith 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 cur
rent generation stuff to go on sale), your time has just about arrived: Dura-A
ce 7900 is scheduled to land in stores this fall.