Will a 12-30 cassette work with a short mech?

glasgowbhoy

Looking at a bigger cassette for long days of climbing in the mountains. I normally run a 12-25 on a standard double chainset but noticed high on bikes have a 10 speed ultegra 12-30 cassette for sale at about £30. I was thinking a 28 would be enough but apart from maybe having to add a couple of links to the chain will the 30 run on a short reach rear mech?

DiscoBoy

Probably not. But specifically which mech?

glasgowbhoy

Cheers, it's a dura ace 10 speed mech.
Maybe 28 is the limit without having to change to a long reach rear?

iron-clover

Which rear derailleur do you have at the moment?
You should be able to find the maximum tooth count it can take. Assuming you have an Ultegra 6800, the short cage can take a maximum cog of 30t, with max chain wrap of 34t. The 'long' cage has max cog of 30t with max chain wrap of 40t.

Assuming you have a compact of 34.50t on the front and a cassette of 11-30t, you'll need a chain wrap of 43t using the formula (50-30)+(34-11). However, the long cage deraileur will probably still work with this setup, assuming the stated max chain wrap is a cautionary underestimate.

iron-clover

Just looked p the 7900 rear derailleur and it says you have a chain wrap of 34, and can take up to 28t with a compact chainset.
Any more and you'll need the long cage.

glasgowbhoy

iron-clover wrote:

Just looked p the 7900 rear derailleur and it says you have a chain wrap of 34, and can take up to 28t with a compact chainset.
Any more and you'll need the long cage.

So, will the 25 I have at the moment on a standard 39 /53 be the most
The 7900 short mech will take ?

DiscoBoy

iron-clover wrote:

Just looked p the 7900 rear derailleur and it says you have a chain wrap of 34, and can take up to 28t with a compact chainset.
Any more and you'll need the long cage.

53-39= 14
28-11= 17
14+17= 31

So 28/11 is fine with a 53/39

53-39= 14
30-12= 18
14+18= 32

And a 30/12 is fine from a capacity point of view. But it exceeds the sprocket size, so "officially" it won't work. Whether or not it will fit with the b screw let out a lot, is another question (to which the answer could well be yes, and I imagine that people will have tried).

glasgowbhoy

DiscoBoy wrote:

iron-clover wrote:

Just looked p the 7900 rear derailleur and it says you have a chain wrap of 34, and can take up to 28t with a compact chainset.
Any more and you'll need the long cage.

53-39= 14
28-11= 17
14+17= 31

So 28/11 is fine with a 53/39

53-39= 14
30-12= 18
14+18= 32

And a 30/12 is fine from a capacity point of view. But it exceeds the sprocket size, so "officially" it won't work. Whether or not it will fit with the b screw let out a lot, is another question (to which the answer could well be yes, and I imagine that people will have tried).

Great , many thanks , I'll play safe and get an 11-28

Cheers

DKay

12-30 should be fine. With the caveat that some rear mech hangers don't allow the B-screw to be adjusted far enough.

I'm running a 12-30 cassette with a compact crankset and a short cage 6700 rear mech with no issues.

dilatory

Mine said 28 was max but took a 30 like a champ.

johngti

I have a brand new 5700 rear mech ready to go onto a new bike - on the box it says that the maximum number of teeth on the cassette is 30. It's a SS 105 mech. Take that as you will! (I'll be using it with a tiagra 12-30 cassette)

philwint

dilatory wrote:

Mine said 28 was max but took a 30 like a champ.

Ditto (Ultegra)

slowbike

johngti wrote:

I have a brand new 5700 rear mech ready to go onto a new bike - on the box it says that the maximum number of teeth on the cassette is 30. It's a SS 105 mech. Take that as you will! (I'll be using it with a tiagra 12-30 cassette)

brand new short 5700 rear mech - worked fine on a 30-12 on a bike that came with 25-11 - no adjustments required.

greasedscotsman

Used a 12-30 with a Dura Ace 7900 short cage mech when I went to the TdF last year.

ba68

Works on my Planet X Sl pro with the older Ultegra6700 short mech, clearance is vey tight when on big / big but it works.

ronny123

Short cage 6700 48/34 12-30 works perfectly. Whether it works or not depends on weather you can get adequate clearance between the biggest cog on the cassette the top jockey wheel using the b-screw.