The Shimano Dura Ace CS-7900 cassette provides you with a wealth of gearing options unlike any previous generation of Dura Ace. You get an unprecedented 8 different ratios to choose from -- 11-21, 11-23, 11-25, 11-27, 11-28, 12-23, 12-25, and 12-27. The low 6 cogs are steel, and the high 4 cogs are made from titanium. Compared to the CS-7800 cassette, you get a weight savings of 10g (e.g. the 11-23 weighs 163g).

The backbone of the Dura Ace CS-7900 cassette is its new aluminum carrier unit. Not only is it lighter than the CS-7800's, but it offers a measurable increase in rigidity for improved power transfer when you're putting the hammer down. In addition, Shimano did some re-engineering to the cog teeth profiles. They're fine-tuned to mate to the Dura Ace CN-7900 chain -- giving you superior shifting on both up-shifts and down-shifts. You'll also experience added drivetrain efficiency since the inner plates of the CN-7900 precisely fit the cog teeth of the CS-7900 cassette. Lighter, stiffer, crisper -- you get improvements all around.

The Shimano Dura Ace CS-7900 cassette has an MSRP of $300. The CS-7900 cassette is compatible with the Dura Ace RD-7900 rear derailleur and the RD-7800 rear derailleur except for 11-27 and 11-28 . The RD-7800 rear derailleur does not have ample chain wrap capacity to handle the CS-7900 in 11-27 and 11-28. These cassettes must be used with the RD-7900. The CS-7900 is optimized for the Dura Ace CN-7900 chain, but it is compatible with the Dura Ace CN-7801 chain.

Two brand-new ratios for Shimano with the Dura Ace CS-7900 cassette are 11-25 and 11-28. The breakdown of the cogs for each is as follows. The 11-28 is 11,12,13,14,15,17,19,21,24,28. And the 11-25 is 11,12,13,14,15,17,19,21,23,25.