Shimano 105 rd5600 capacity

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I have the above derailleur and the cassette currently on the bike is 11/25 I am trying to find out if the derailleur can handle more than a 25 tooth sprocket but google isn’t playing ball, any help appreciated
...I can’t find any other markings or numbers on the derailleur
 

iluvmybike

Über Member
It will take up to a 27t big sprocket
 

fossyant

Ride It Like You Stole It!
Location
South Manchester
@fossyant I hadn't noticed that , the joys of doing the initial post on my phone..
Hate posting on a phone with my fat fingers and an 'edge' phone, my fingers dont go round corners well.
 
Location
Loch side.
Derailer capacity is misunderstood, it seems.

Capacity relates to how much "throw" the derailer can offer so that a chain doesn't become too slack or too tight, depending on the gear combinations up front and back. If the chain is on small in the front and small at the back, the derailer cage needs to swivel back in order to keep the chain tight. If the chain is on big in front and big at the back, then it needs to swivel forward in order to release some length of chain to wrap around the big gear combo.
A short cage derailer has a small capacity and a long-cage one a large capacity. This makes sense if you consider the size of the arc described by the movement of the jockey cage.

To calculate the capacity of your "system", look at the largest and smallest chainring. Ignore the middle one. If the largest is 52 teeth and the smallest one, then deduct 39 from 52. That gives you a difference of 13. Park that in your memory for now.
Move back and look at the biggest and smallest on your cassette. If your biggest is 28 and your smallest is 13, then you have a difference there of 15. Recall the 13 from memory, add it to 15 and you have 28. That means you have a difference of 28 teeth in the two extremes and you need a derailer that can handle at least 28. If yours has a capacity of only 25, you're in trouble. If it has more, you are OK and ditto for if its capacity is 28 on the dot.

If you over-reach the capacity, then in the smallest combination the derailer cage will move backwards (when in the small-small combo) to the horizontal position where it can no longer offer the chain any tension. With a bit of a rattle and shake, the chain can get snagged and you will rip the derailer out of the frame. At the other extreme, you will stretch the jockey too far forward (beyond 45 degrees is bad) and it will damage the bottom pulley and possibly, derail it so that the chain snags and rips the jockey out of the frame and into the spokes.

That's capacity.

Maximum sprocket size capability is another thing. That tells you only how big your largest sprocket on the cassette can be, nothing else. This relates to the jockey's B-screw adjustment range and how far the jockey will allow the top pulley to move downwards out of the large sprocket's way.

The example above of the short cage RD with the 30-tooth sprocket doesn't tell us whether the system is liable to snag, but my guess is that that set-up is not optimal.
 
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