2009 Dura-Ace (7900) versus 2008 Dura-Ace (7800) weight comparision (Source: Shimano)
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Shimano has moved into revolutionary new technology with a hollow chainring design. The outer chainring is 100% hollow, reducing weight and increasing stiffness by 20%. The chainring teeth have also been redesigned for improved chain contact and transfer of power. Bottom bracket seals have been revamped for smoother rotation and a longer service life.
As seems to be the current market demand the 7900 chainset will also be offered for the first time in a Dura-Ace branded compact ratio- 50/34T (FC-7950). There will also be triathlon/time-trial specific ratios: 54/42T, 55/42T and 56/44T whilst the crank arm lengths for the entire range will be 165-180mm (going up in 2.5mm increments).
Initial weight predictions were that the chainset and BB would equate to a 50g saving over the current 7800 chainset = 690g including BB, but the latest stated weight we have is 725g, which would only be a 15g saving!
STI Levers and FlightDeck
The 7900 STI levers get a completely different look and feel. Very significant is Shimano’s first ‘under bar tape’ cable routing, with friction being kept to a minimum with a new PTFE coated inner cable. The lever blades are made of carbon and feature a reach adjust mechanism – ideal for people with smaller hands and a shorter reach. Shifting stroke is also reduced by 20% for faster shifts.
The shifters also feature integrated buttons to operate the new wireless FlightDeck computer with the need to take the hands off the handlebar. The new FlightDeck system will measure data such as heart rate, altitude, inclination, cadence, gear position and more. It works via a coded signal to prevent cross talk and interference, and is also PC downloadable. (We will have to wait and see about Mac compatibility)
With the help of a titanium fixing bolt and band the new STI levers come in at 50g lighter than the current 7800 version at 370g per pair. New bar-end shifters and down tube shifters will also be available to match the new 7900 groupset and a full carbon bar-end brake lever for aero bar setups will also be available.
The new CN-7900 chain features a re-useable quicklink (SM-CN79) that can be connected and disconnected without the need for tools. A directional chain is also pretty revolutionary by current standards, enabling the outer plates to be designed specifically to interact with the chainrings and the inner plates to work with cassette sprockets. Overall the results should be an even slicker shift than the current drive train, and quieter running.
The chain has also been developed with hollow pins and perforated inner plates to help make it lighter – weight of the 7900 chain stands at 251g making it 20g lighter than the current CN-7800 model.
The rear derailleur is designed to be compatible with 28T cassette sprockets so one mech can cope with the entire range and is also compatible with compact chainset (FC-7950). A full carbon pulley wheel plate helps reduce weight to 166g.
The front derailleur has lower spring tension and leverage ratio, to work specifically with the new ST-7900 levers, for lighter action shifting. Trimming the mech when it is on the outer chainring position is no longer necessary thanks to a redesigned cage. Weight is only 68g.
The new brakes have an enhanced brake arch, increasing the linear response and making them even more powerful than the already impressive 7800 brakes, with more modulation too. A lower cable clamp ensures better cable routing and reduced friction. The Dual-Pivot design has titanium hardware to get the weight down to 287g a pair.
Also new is an improved brake pad compound, which sounds too good to be true, boasting twice as good stopping power in the wet, 20% improvement in the dry, and overall up to 50% less wear.
Shimano has reworked the cassette sprocket carrier to produce a super lightweight yet very rigid cassette. The separate sprockets have also been redesigned for more robust shifting performance and further weight saving. This 10-speed Hyperglide cassette will be available in a much wider range of combinations: 11-21T, 11-23T, 11-25T, 11-27T, 11-28T, 12-23T, 12-25T, 12-27T. Weight is 163g (11-23T).