need new cassette , current cassette is dura ace 7900 with 4 largest cogs being ti . what is the difference between the 7900 10 sp cassette and the 7800 10 speed cassette which also uses ti cogs I believe ? I'm using the kmc 10 sp xl chain.

I'm interested by this too. I currently use the 7800 and would like to know if it's worth paying the extra for 7900. The rest of my groupset is 7900 and I use a KMC X10SL chain.

7900 has a little more machining. most evident when looking at the back of the spider. also available in a greater range of sizes (11-25, 11-27, 11-28, etc)

7900 Product page

7800 Product page

Looks like about 10g weight difference for the 11-23, 7800 cassettes that start with 11t only have 3 Ti cogs, & the 7900 has more size options.

thanks all for the replies , I've been using the 7800 and it shifted very well until it and the chain wore , bought a new kmc chain and was hoping it would shift ok with out changing the cassette but tis not the case ., the 4 ti gears are worn and the shifting is slugish there , after reviewing the product page I think I will buy a new 7800 ,it's 10 gr more but 40.00 less .thanks all for helping me with this question . cheers

thanks for the produce page post ozdavo , helped a lot . cheers