New mechanical Shimano Dura-Ace 7900 prototypes
By James Huang, technical editor | Thursday, April 10, 2008 11.30am
Reach adjustment on the new levers looks to be accomplished via the small set screw James Huang
The rumours 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. But there hasn't been much in the way of detail shots yet… that is, until now.
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 Ghent-Wevelgem classic with second-generation prototypes from the Japanese component giant. Our long-awaited first-person encounter suggested some additional details as well as confirmation of a few mechanical workings that will likely make their way on to the production version when it is eventually released.
The new Dual Control levers 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 even smoother.
The rear derailleur prototype at Ghent-Wevelgem was fitted with the expected carbon fibre 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 reasonable that Shimano could shave a little weight here by going away from forged aluminium.
Otherwise, the overall configuration is 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 aluminium cage and forged aluminium 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 calliper prototypes looked 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.
You can follow BikeRadar on Twitter at twitter.com/bikeradar and on
Facebook at facebook.com/BikeRadar.
can also improve your fitness and train with us on training.bikeradar.com.