Largest rear cog that will fit *my* DA7900 rear mech

Ben6899

Now then,

I'm currently running DA7900 with 53/39 at the front and a SRAM 12-27 at the back.

Does anyone have experience of what size cog I can go for when speccing a climbing cassette? It seems like a small increase, but I'd like to find a 12-29 cassette as those additional 2.5 gear inches make all the difference down that end of the range!

I know this comes down to how much wrap the mech can accommodate (it's a short cage as you might guess) and the clearance available for the largest cog. I think 12-29 gives a required rear mech capacity of 31 and a large cog size of 29.

(According to Shimano this doesn't go with a short cage rear mech - 29 and 27 are the respective numbers quoted)

clazza

I think it depends on the dropout design / B-screw...not sure to look for there but I successfully used a 32 with a 7900 in the past.

svetty

Yes will vary according to chainstay length and drop-out. A 30 is almost certain to work, larger than that is a bit more variable......

lesfirth

Svetty wrote:

Yes will vary according to chainstay length and drop-out. A 30 is almost certain to work, larger than that is a bit more variable......

I do not question your knowledge but how does chainstay length come into this? :?

Ben6899

Interesting thoughts, chaps. Appreciated.

I suppose I could lump on a Tiagra or something 12-30 and see how I get on. Not the end of the world if it doesn't work.