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Race Tech: Gent-Wevelgem, April 9, 2008
Gotcha! New mechanical Shimano Dura-Ace 7900 prototypes spotted
By James Huang in Deinze, Belgium
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The rumors have been circulating for months, we've already posted a heap of technical info and there have been a few grainy photos of Shimano's upcoming Dura-Ace 7900 mechanical group. However, there hasn't been much in the way of detail shots available yet… that is, until now.
It is well known that the Rabobank team has been field testing the 7900 prototypes for some time now and after a brief respite, at least two riders departed from Deinze, Belgium in this year's Gent-Wevelgem classic with second-generation prototypes from the Japanese component giant. We won't bother reiterating what we've already told you but our long-awaited first-person encounter certainly suggested some additional details as well as confirmation of a few mechanical workings that will likely make their way on to the production version whenever it is eventually released.
The new Dual Control levers indeed retain the familiar twin pivoting design and the reach adjustment on these prototypes was accomplished via a small set screw located within the lever body. Also as previously reported, the hood shape has grown markedly flatter up top and the overall girth has increased a bit as well for a more substantial grip.
The derailleur and brake housings are both routed beneath the tape as is now commonly known but these second-generation prototypes allow the derailleur housing to be run either behind or in front of the bar, much like Campagnolo and SRAM Red. Unlike those competitors, though, there are no sharp housing bends required coming out of the lever so the shift action is expected to be more even more friction-free.
The rear derailleur prototype at Gent-Wevelgem was fitted with the expected carbon fiber cage (both inner and outer plates) but we were surprised to also find it equipped with a composite forward knuckle. As this bit isn't subject to nearly as much stress as the main pivot housing up top, it seems perfectly reasonable that Shimano could shave a little weight here by going away from forged aluminum.
Otherwise, the overall configuration is rather familiar although the leverage arm attached to the cable anchor point is clearly a bit longer to accommodate the larger cable pull ratio that will reportedly be unique to 7900. The front derailleur looks to be mostly an evolution of the current 7800 bit with a plated aluminum cage and forged aluminum links with widely-spaced pivots.
The chain is a notable change from current Shimano offerings, though, with its asymmetrical outer plate profiling and relieved inner plates. More weight is saved with the hollow pins, although we couldn't find the reported master link in these early prototypes.
The Rabobank riders looked to be riding current 7800 cassettes and crankarms but the outer chainring was obviously a test mule of some sort. There wasn't too much we could tell just by appearances, though, so we'll just have to assume that Shimano is continuing to refine its shift pin technology.
The brake caliper prototypes looked absolutely fantastic and we have every reason to believe that they will be both significantly more rigid and lighter than the existing Dura-Ace stoppers. The upper arm stands more upright and is far beefier which should yield more power and a better feel at the lever but the backside of that entire arm is surprisingly aggressively milled away. Even so, the machine work on this prototype leaves all of the critical surfaces and edges intact so there's no reason to suspect that it has softened things up in the process.
Photography
For a thumbnail gallery of these images, click here
Images by James Huang/Cyclingnews.com
- Ha, we found you! The mechanical version of Shimano's upcoming new Dura-Ace group was found on several Rabobank riders' bikes at Gent-Wevelgem.
- There has apparently been a little bit of confusion as to how the new levers would function…
- …but Shimano has clearly retained the standard twin pivoting levers for the new Dura-Ace 7900 Dual Control levers.
- The levers were clearly still in prototype form but it looks like Shimano is pretty close to settling on final specs.
- Reach adjustment on the new levers looks to be accomplished via the small set screw (we'd imagine there's an access port on the other side).
- As already mentioned on multiple occasions , the derailleur housing is finally routed beneath the handlebar tape…
- …but it was news to us that the derailleur line could be run either in front of or behind the bar.
- Styling-wise, the prototype rear derailleur looks to be mostly an evolution of the current version (the production one will most certainly use smoother-edged forged bits).
- Not many changes to report with the usual Slant Parallelogram geometry.
- Both cage plates are carbon fiber.
- The forward knuckle is also crafted of composite material , presumably to save weight. We'd be surprised if this feature didn't make it to production as molds have clearly been cut.
- The front derailleur is likewise still just a CNC-machined prototype but the styling elements are still there.
- The cage is still made from plated aluminum.
- Like the current version , pivots are widely spaced for rigidity.
- Ok, it's a prototype , but it's probably not all that far off from what we expect to see this fall.
- The prototype Dura-Ace 7900 chain looks to be far lighter than the current one with its hollow pins and relieved inner plates.
- Rabobank's outer chainrings were clearly test mules of some sort…
- …although it looks like Shimano engineers are primarily just working on new shift ramp patterns.
- Sorry, no new cassette to see here. This is the current 7800 version.
- The brake, however, is clearly a working prototype of the new group and it looks superb.
- Aggressive milling cuts weight but retains stiffness by virtue of the intelligently selected areas of machining.
