HG50 11-25 swapped for 12-32

[sayek1]

I have swapped out my 11-25 for a 12-32 (£20 Wiggle), but am now getting the 105 Derailleur rubbing on the 32t sprocket. Does anyone have any answers here - can I swap the derailleur or will a longer chain sort it. The bike is a Genesis CDF.

I recently swapped my SRAM on my other bike for something similar and ended up having to swap the derailleur & chain, but this time someone on the Wiggle site said you wouldn't need to.

Don't really want to fork out for a new chain on the off-chance as this one has done less than 200miles!!!

 

[Sleeping Menace]

It may well be a case of both new chain (since you're adding 7teeth) as well as swapping rear mechs to something which doesn't object to the 20t step in your cassette gearings. Looking at how my rear mechs sit against the 10-23, and 12-25 here.. there's no way either would be able to work its' way up to a 32 tooth cassette. you'll certainly need a 'long cage' rear mech to handle all the chain slack from the 20t variation.. beyond that, I'm not entirely sure what direction to point you in.


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[fossyant]

You'll need a few more links in the chain, but if it's a short cage mech, it will struggle with a 32.

 

[Gerry Attrick]

105 derailleurs are specced for a 27 tooth sprocket max.

 

[Banjo]

Interested to read that, I was thinking of changing from105 11/25 cassette to 11/28

the chain needs changing anyway but hadnt budgetted on a new rear mech as well. Anyone know if it will work? I have heard that you can go a bit further than the spec.

 

[RecordAceFromNew]

If you haven't adjusted the B screw, you should read this and try see whether a) the cassette can clear the upper jockey wheel and b) rear mech has enough wrap range for your set up. The number of extra teeth beyond spec a mech can handle is not just dependent on the mech or cassette, but is also frame/hanger geometry dependent, hence there is no general hard and fast answer.

 

[andrew_s]

You will need an MTB rear mech for a 32T cassette.


A 30T cassette can sometimes be made to work by fiddling with the chain length and B screw, but whether it works will depend on how long the gear hanger on your frame is.
28T normally works OK.

 

[sayek1]

Thanks guys.

Is there an MTB derailleur that will work with Tiagra shifters?

 

[Garz]

Interested to read that, I was thinking of changing from105 11/25 cassette to 11/28

the chain needs changing anyway but hadnt budgetted on a new rear mech as well. Anyone know if it will work? I have heard that you can go a bit further than the spec.

I think you can get away with this one, anything above 28 though and time for a long cage.

 

[RecordAceFromNew]

Thanks guys.

Is there an MTB derailleur that will work with Tiagra shifters?

In general Shimano and Shimano compatible mountain rear mechs are compatible with your Tiagra rear shifter. Their MTB front mechs aren't compatible with their road front shifters, however, but that shouldn't concern you here.

 

[sayek1]

Any ideas on a model that would work. Thanks

 

[mcshroom]

Most Shimano mtb rear mechs should work. As for which one, it depends on budget. Deore is probably a good compromise between price and quality, but you could easily go up (XT etc.) or down (Alivo). I have an altus rear mech on my tourer and it works perfectly happily with a 2300 shifter and a 11-32t cassette

 

[Russell Allen]

an 11-28 is the largest for a 105 mech, and the chain will now be to short. Remove the cassette before it destroys your deraillier, hanger, wheel and maybe frame. ..........Urgently. The rear mech is way to short for a 32T

105 cassette manual

Russell

 

[frank9755]

As the posters above say, any Shimano mountain bike mech would work.

What you have converted to is in fact the standard set-up you get on most new touring bikes such as a Dawes Galaxy or Ridgeback Panorama / Voyage. I also did the same mod on my first racing bike.

I'd recommend an LX. That is what Dawes uses and it has worked for me with no problems, but others would work fine too.

Do you have a triple chainset? If not you don't need a long cage. It would work ok but a medium cage would probably shift slightly better. If you do have a triple, then you need long cage.

Agree with the suggestion of getting a new chain, too.

Good luck. I'm sure you won't regret the change. I didn't!

 

[andrew_s]

Thanks guys.

Is there an MTB derailleur that will work with Tiagra shifters?

Watch out for "rapid rise" or "low normal" MTB rear mechs, which exist as an alternative to the traditional top normal mechs.
These work the opposite way round to road mechs, so the main lever would shift to a higher gear/smaller sprocket, and the inner lever to a lower gear/larger sprocket. This would be confusing.
Low normal mechs can be spotted because the cable clamp is on the inner parallelogram plate rather then the outer one.