Ultegra Chain Capacity

corvus13

I'm currently running on 50-34 chainwheel and 12-25 cassette, a chain capacity of 29. (Surely I can't have got this wrong?). Now I have the jockey wheels at 90 degrees to the horizontal when on big ring and small cog i.e. 50x12 as recommended by the Shimano Tech Service Instructions. This should work but on 50x25 (chain capacity=29) the derailleur is frighteningly streched out. Ok this is not an ideal combination but
1, this is considered fine by Shimano.
2, Shimano advise a maximum capacity of 33, in this case 50x29. Horrible to visualise.
This is as I understand it yet what I'm looking at does not seem healthy.Where am I going wrong?
Cheers Tim

Bobbinogs

err, sounds like a chain length issue rather than a capacity one. There are a few easy ways to determine the correct length (old school is to wrap the chain around big ring/big cog without the rear derailleur and add 1 inch). I use this online tool which works well:

http://www.machinehead-software.co.uk/b ... hcalc.html

desweller

Derailleur capacity and chain length are not the same thing.

When you set chain length, you're looking to get the chain as short as possible whilst still being long enough that you can use the biggest chainring in combination with the biggest sprocket in your rear gear cluster. The derailleur will look stretched out in this combination.

Derailleur capacity is a measure of the range of sprocket sizes the derailleur can handle.

corvus13

Bobbinogs, Shimano suggest that with a big ring x small cog combination, the jockey cage should be 90 degrees to the horizontal (this should account for the chain length) and accept a total capacity of33 or less. These are Shimano's words and yet.....

corvus13

Hopefully this link will work. www.shimano.com/.../SI/SI_5X90B/SI-5X90 ... _m565775...

Mad_Malx

Your link isn't working for me, but I'm with the previous posters.
If your derailleur is stretched it's because the chain isn't long enough and you need to add links.

Shimano's capacities are generally conservative and you can probably get away with a slightly bigger difference than they say.

Edit - just played with my gears (bike is sitting next to my desk):
I am running Ultegra short cage 50-34 with 12-27 at the back.
On 50x12 my derailleur hangs nearer 7 o'clock than 6 (vertical). Fully crossed 50x27 the derailleur is stretched to almost 4 (not surprisingly) but could still stretch further. On 50x25 it's at about 5 o'clock.

I don't have any problems with shifting or chain being too loose on the little rings.

crankycrank

Agree with the others that the chain is probably too short. Chain length instructions work most of the time but not always. I have close to the same gearing as the OP (cassette is 13-25) and use the 13-50 combo quite a bit in stop and go city traffic. I probably have my chain 2 extra links longer than most guides would recommend as most would have my derailleur stretched to the limit if it were shorter and I never use the 34-13 so no worries about being to loose and it works flawlessly. Someone who never uses the large ring-large cog combo may do better with a slightly shorter chain. Best just to check the length according to the gearing you'll be using.

Bobbinogs

corvus13 wrote:

Hopefully this link will work. http://www.shimano.com/.../SI/SI_5X90B/ ... _m565775...

That link doesn't work for me but I would ignore it anyway! Personally, if I had the same problem I would measure the chain length the old school way, get a second opinion via the online tool and then see how the current length varies. I suspect you are up to one inch too short, which can make all the difference (better to round up long rather than short, IME).