COG compatibility
03-09-14, 03:30 PM
#1
Junior Member
Thread Starter
Join Date: Apr 2012
Location: Ca
Posts: 24
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
COG compatibility
I have ultegra 6700 shifters, rear dérailleur, and a 12-25 cog. Is there a COG that has a 30 tooth gear that would work with my current setup?
03-09-14, 03:57 PM
#2
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,725
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5793 Post(s)
Liked 2,584 Times
in
1,432 Posts
A bit more info would certainly help. Such as the number of speeds, short or long cage, and chainring combination.
But in general, RDs have a capacity based on two considerations. The largest sprocket they can clear, and the chain take up capacity, expressed as the sum of the differences largest to smallest, front and rear. For example, if you have 39/53 chainrings, and a 12-25 cassette you need 14+13 or 27 teeth of take up capacity.
Those capacities are listed by the maker on their spec's page. However, there's usually some fudge room, so I find I can routinely exceed them by about 10% or so.
So you can work this out for yourself, by checking system capacity and then shopping among the various cassettes to fit the system.
But in general, RDs have a capacity based on two considerations. The largest sprocket they can clear, and the chain take up capacity, expressed as the sum of the differences largest to smallest, front and rear. For example, if you have 39/53 chainrings, and a 12-25 cassette you need 14+13 or 27 teeth of take up capacity.
Those capacities are listed by the maker on their spec's page. However, there's usually some fudge room, so I find I can routinely exceed them by about 10% or so.
So you can work this out for yourself, by checking system capacity and then shopping among the various cassettes to fit the system.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
03-09-14, 05:10 PM
#3
Expired Member
Join Date: Jun 2007
Location: TN
Posts: 11,547
Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 3674 Post(s)
Liked 5,438 Times
in
2,764 Posts
Any 6700 rd will take a 28t cog and the newer ones will take a 30t by design. 6700A? Anyway, it also depends on the derailleur hanger so you will just have to try it. The chances are good however, and a Tiagra 12-30 cassette is only about $25 so it's worth a try. Need a new properly sized chain as well.
