11-25 to 12-28 ?

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11-25 to 12-28 ?

Postby dav3e » Fri Feb 08, 2013 12:19 pm

I was looking to change my cassette from an 11-25t to a 12-28t, but was told that this might not work as my Shimano105 derailleur is a shortcage version (with a 50-34 compact chainring). Could anyone tell me if this true or not ? Thanks in advance.

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Re: 11-25 to 12-28 ?

Postby jomoj » Fri Feb 08, 2013 13:09 pm

105 short cage derailleurs will go up to a 28, there's also a version that will go to 30 but yes you'll be fine, just might need to adjust the screw on the hanger if the jockey wheel is hitting the sprockets

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Re: 11-25 to 12-28 ?

Postby sungod » Fri Feb 08, 2013 13:46 pm

go to http://techdocs.shimano.com

look at the SI-* document for the exact model of 105 rear mech (i.e. 5500, 5600, 5700), check the specification

there are two numbers that matter

i) the maximum sprocket size
ii) the maximum capacity, capacity is the sum of the differences between largest-smallest on front and rear, so for 50-34 and 11-28, the capacity will be 16+17 == 31

for short cage 5700-a for instance, the figures are 30 and 34 respectively, so you'd be ok

if the results are within specification, follow the set-up instructions for the rear mech in the SI-* document, including for chain length

if the results are not within specification, but only slightly over, you may be able to get away with it, but there may be problems with chainslap on smaller sprockets, and if you went on largest-largest there's potential for something much nastier to happen
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Re: 11-25 to 12-28 ?

Postby Dave_P1 » Fri Feb 08, 2013 19:59 pm

I run a 28t on my 105 derailleur without any problems, you will be fine.

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Re: 11-25 to 12-28 ?

Postby Macerello » Fri Feb 08, 2013 20:08 pm

I switched to a 28 with my 105 derailleur too without any problems.

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