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Old 05-17-09, 01:58 PM   #1
kipibenkipod
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Rear derailleur - cassette 28 to 32 - do I need to replace?

Hi,
I have 8 speed Shimano RSX with rear cassette of 28.
I bought a new cassette of 32.
Should I also replace the rear derailleur or it will be able to shift with the new cassette?

Thanks,
Kfir
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Old 05-17-09, 02:36 PM   #2
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You're probably OK. The potential worry is whether or not your specific rear derailleur can fit with a rear cog as big as 32t; if you can find the specific model number of your derailleur, we can probably look up the specs. Often on Shimano derailleurs the model number is stamped on the inside of the main body (on the side facing the wheel).
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Old 05-17-09, 02:42 PM   #3
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You're probably OK. The potential worry is whether or not your specific rear derailleur can fit with a rear cog as big as 32t; if you can find the specific model number of your derailleur, we can probably look up the specs. Often on Shimano derailleurs the model number is stamped on the inside of the main body (on the side facing the wheel).
I will check it when I go home.
So, basically I need to replace the cassette and see if the gears are changing?

Thanks,
Kfir
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Old 05-17-09, 04:25 PM   #4
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I think the issue, have to do with whether the chain is long enough for the larger cassette, and if the RD has the capability to adjust to a now bigger range. If you have a 'long cage' RD there should be no problem with it handling the range but the chain length still may have to be lengthened.
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Old 05-17-09, 07:38 PM   #5
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wm, thanks for adding key additional info. The main thing that I was referring to was whether the upper wheel of the derailleur will physically clear the new biggest rear cog (go low enough).
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Old 05-17-09, 09:04 PM   #6
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wm, thanks for adding key additional info. The main thing that I was referring to was whether the upper wheel of the derailleur will physically clear the new biggest rear cog (go low enough).
That's a good question. Modern Shimano road derailleurs have a stated maximum cog size limit of 27 teeth. They will accept a cog larger than 27. How much larger is a point of discussion and often disagreement. Try the 32 with your derailleur, you will probably need to adjust the "B" screw and may need to replace it with a longer screw. Or you can try putting the screw in backwards. If your current derailleur will not clear the largest cog then you'll need a mountain type derailleur, and that will work.
Rear derailleurs have two limits, the size of the largest cog, and the chain wrap capacity. These two limits are often misunderstood. The length of the cage determines how much chain slack can be wrapped by the derailleur. This is a function of the difference in sizes between the largest cog and smallest cog added to the difference in sizes of the largest chainring and the smallest chainring. The largest cog limit is a function of the geometry of the upper trapezoidal part of the derailleur. Mountain type rear derailleurs are designed to accept a much larger cog than a road type.

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Old 05-17-09, 09:14 PM   #7
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The RSX was available in a long cage version. If you have that one, then it will work fine. The short cage version really won't work properly with cogs larger than 28t.
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Old 05-18-09, 07:35 AM   #8
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Originally Posted by Mondoman View Post
You're probably OK. The potential worry is whether or not your specific rear derailleur can fit with a rear cog as big as 32t; if you can find the specific model number of your derailleur, we can probably look up the specs. Often on Shimano derailleurs the model number is stamped on the inside of the main body (on the side facing the wheel).
Thanks all for your input.
The Model of the RD is: Shimano RD-A416
The bike is Dawes Galaxy World Tour and its a touring bike.
I would appreciate you checking the model to see if it will work.

Here is a photo of the bike. Hope it will help.


Thanks,
Kfir
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Old 05-18-09, 07:36 AM   #9
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Originally Posted by wmodavis View Post
I think the issue, have to do with whether the chain is long enough for the larger cassette, and if the RD has the capability to adjust to a now bigger range. If you have a 'long cage' RD there should be no problem with it handling the range but the chain length still may have to be lengthened.
Hi,
I will replace the chain with a new one. So this will not be an issue.

Thanks,
Kfir
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Old 05-18-09, 10:45 AM   #10
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Shimano RD-A416 has GS and SS (Long and short cage)

Hi,
Hehe, a little search shows that RD-A416 has 2 types:
RD-A416-SS - Short cage
RD-A416-GS - Long cage

Now, on my RD its written just RD-A416
What do you think?

Thanks,
Kfir
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Old 05-18-09, 10:57 AM   #11
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Ok,
I found this at forum.ctc.org.uk.
A link to this post
Quote:
Re:I can't get bottom gear running smooth.

Postby CJ Thu May 04, 2006 9:44 am
Regarding RSX, it depends. When it was 7-speed the RD-A410-SS (short) and GS (long cage) mechs were both rated 28T max sprocket, but when the group went 8-speed (denoted by RD-A416 on the back of the parallelogram) Shimano increased the GS to 30T. But it looks pretty similar and as PW suggests, maybe Shimano simply fitted a longer "B-tension" screw!

But you've probably got RD-A410, and if it's working okay that's probably because the Galaxy has a longer gear hanger. A MTB mech will work better nevertheless, since its steeper slant allows it to clear the fat end of the cassette whilst remaining close enough to the thin end for slick shifting across the whole range.
Reading all the thread, I understand that it could be done, but I'm not sure.
Can someone proof read this thread and see if it is possible to use 32 cassette?

Also, here is a diagram of the RD:

Thanks,
Kfir
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Old 05-18-09, 02:03 PM   #12
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That diagram shows a short cage and a long cage. If you compare the diagram with what you have maybe you can decide which it is. The length of part #13 is the difference.
My recollection is that RSX was a road group, not a mountain group. Modern Shimano road derailleurs are rated for 27 teeth, but as previously stated, will take more, but 32 is a stretch.
The length of the cage does not dictate the cog size limit.

Last edited by Al1943; 05-18-09 at 02:13 PM.
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Old 05-18-09, 06:24 PM   #13
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Quote:
Originally Posted by kipibenkipod View Post
The Model of the RD is: Shimano RD-A416

Here is a photo of the bike. Hope it will help.
Wrong side!

But still good enough to see that you have the long cage RD (which makes sense with the triple up front.)
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Old 05-19-09, 02:04 PM   #14
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Wrong side!

But still good enough to see that you have the long cage RD (which makes sense with the triple up front.)
Hi,
Thanks all for your replays.
It looks like this cage is the GS model.
So thanks.
I will buy the chain, and try to replace the cassette and see if I'm able to drive it to the 32 cog.

Thanks again,
Kfir
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Old 05-19-09, 02:11 PM   #15
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Odds are you will still need to take a few links off of that new chain.
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Old 05-22-09, 02:26 PM   #16
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Solved ;)

Hi all,
I just got the new chain by mail.
I changed the cassette and the chain, and the RD is working perfectly out of the box.
I need to to so some more adjustments, but amazingly it moved the 32 ring without any problem.
So for the archive:
You can upgrade your cassette from 28 to 32 if you have Shimano RD-A416 GS.

I'm really happy,
Thank you all for your help and support.

Cheers,
Kfir
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Old 05-22-09, 03:09 PM   #17
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Glad it worked -- enjoy riding this summer!
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Old 05-22-09, 03:12 PM   #18
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Glad it worked -- enjoy riding this summer!
Hehe,
Actually its my wife, and we'll take a few months tour this summer So it will be fun

Thanks,
Kfir
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