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Zitat von Sheldon Brown:
Triple Chainrings
For the 2002 model year, Shimano introduced a triple chainring crank set in the Dura-Ace line, with corresponding STI shifters, front and rear derailers. While other Shimano "road" triples come with 52-42-30 chainrings, the Dura-Ace version comes with 52-39-30 rings. At first this seemed like a welcome upgrade, offering greater versatility to the road/touring cyclist.
Unfortunately, the way Shimano chose to do this is rather wrong-headed and retrograde, resulting in a crankset that is even less versatile than the 130/74 "road" triples in the Ultegra, 105, Tiagra and Sora lines.
Instead of using a crankset with two sets of mounting holes, as with other modern triple sets, the 30 tooth chainring attaches to the 39 tooth ring, rather than to the crank itself, in the manner of a Willow Triplizer or a TA conversion chainring. "Oh, great," you say, "so then you can retrofit the 39 onto other 130 BCD doubles!" Well, no. Unlike the Willow and TA conversion rings, the Dura-Ace is specifically designed NOT to fit a standard 130 double crank, because the "shelves" that support and center the middle ring get in the way. The "triple" Dura-Ace crank has had these "shelves" machined off flush, so it is the only crank that can accept this chainring, even though it does still use the standard 130 mm bolt circle.
But wait! It gets worse! Instead of using the standard 74 mm bolt circle for the 30 tooth chainring, as on all of other Shimano "road" triples, Shimano has seen fit to create a brand-new bolt circle pattern just for this application, 92 mm. Thus, there is NO other chainring besides the stock 30 that can be used with the Dura-Ace triple.
I'm generally very supportive of Shimano, but I'm really dismayed by the very unfortunate direction taken with the Dura-Ace triple. What ever made Shimano think the world needs a new bolt circle diameter?
Triple Chainrings
For the 2002 model year, Shimano introduced a triple chainring crank set in the Dura-Ace line, with corresponding STI shifters, front and rear derailers. While other Shimano "road" triples come with 52-42-30 chainrings, the Dura-Ace version comes with 52-39-30 rings. At first this seemed like a welcome upgrade, offering greater versatility to the road/touring cyclist.
Unfortunately, the way Shimano chose to do this is rather wrong-headed and retrograde, resulting in a crankset that is even less versatile than the 130/74 "road" triples in the Ultegra, 105, Tiagra and Sora lines.
Instead of using a crankset with two sets of mounting holes, as with other modern triple sets, the 30 tooth chainring attaches to the 39 tooth ring, rather than to the crank itself, in the manner of a Willow Triplizer or a TA conversion chainring. "Oh, great," you say, "so then you can retrofit the 39 onto other 130 BCD doubles!" Well, no. Unlike the Willow and TA conversion rings, the Dura-Ace is specifically designed NOT to fit a standard 130 double crank, because the "shelves" that support and center the middle ring get in the way. The "triple" Dura-Ace crank has had these "shelves" machined off flush, so it is the only crank that can accept this chainring, even though it does still use the standard 130 mm bolt circle.
But wait! It gets worse! Instead of using the standard 74 mm bolt circle for the 30 tooth chainring, as on all of other Shimano "road" triples, Shimano has seen fit to create a brand-new bolt circle pattern just for this application, 92 mm. Thus, there is NO other chainring besides the stock 30 that can be used with the Dura-Ace triple.
I'm generally very supportive of Shimano, but I'm really dismayed by the very unfortunate direction taken with the Dura-Ace triple. What ever made Shimano think the world needs a new bolt circle diameter?
, linke gibts überall, ist im Grunde ja auch gut so