Rear derailleur set up problem.

[Brandane]

As per usual, replacing one part sets off a "chain reaction" (no pun intended!). Bike is a Specialized Secteur.
I wanted to make the hills a bit easier so replaced my 12/25 cassette with a 12/30, thinking that my existing medium cage Tiagra derailleur would do the job. It doesn't, and the Shimano spec sheet confirms it's suitability up to 27 teeth.

New derailleur arrived yesterday, a Shimano Deore 9 speed long cage. Fitted it when I got home from work (at midnight!) but strangely I cannot get it running correctly. If I set the cable tension so that it runs smoothly on the high gears (small sprockets) then it is too tight for the low gears and the chain is catching on the next biggest sprocket as it turns. If I then set it slack enough to run smooth on the big sprockets, there isn't enough tension for it to change gear on the smaller sprockets. Arghhhhh!

I thought the obvious tension problem, maybe the cable is sticking, so replaced inner cable. No change. Replaced cable outer at derailleur end, slight improvement. Not enough new cable outer left to replace at lever end but it seems to be smooth enough at that end....

I seem to remember having had this problem before, but can't remember how I fixed it. Maybe cable outer at the lever, or am I kidding myself on? Chain length is correct, B screw tension correct, I am stumped!

Edit ... Chain is also new.

 

[sight-pin]

I replaced my 12/27 cassette to a 11/32 with no problems but have a Sora medium rear derailleur, it just needed two extra links on new chain.
Not sure with using Shimano Deore though?
This link may also offer an idea https://www.cyclechat.net/threads/9-speed-tiagra-11-32.117720/

 

[Lonestar]

Yeah I got a 9 cog but only got 8 working.Not that it really bothers me too much.

 

[Levo-Lon]

Tiagra to deore...you have gone to a different pull ratio.. it will not work properly with your shifter.

 

[winjim]

Are you sure the Tiagra mech doesn't work? I run a 9sp Sora short cage mech with an 11-30 cassette and it just about works, the limiting factor being total capacity rather than maximum sprocket size.

 

[mjr]

Tiagra to deore...you have gone to a different pull ratio.. it will not work properly with your shifter.

http://forum.ctc.org.uk/viewtopic.php?f=5&t=38039 suggests it should be the same pull ratio, unless I've misunderstood.

But I'm a friction fan

 

[Brandane]

Tiagra to deore...you have gone to a different pull ratio.. it will not work properly with your shifter.

The same set up works perfectly on my Tricross - Shimano Tiagra 9 speed shifters with the identical Deore rear derailleur - which is why I went for the same on the Secteur.
I have just been for a 18 mile ride and for some reason it has started working a lot smoother than it was previously. Still not as it should be though, and I tend to be a bit anal about these things , so my quest to get it right continues!

 

[Brandane]

Are you sure the Tiagra mech doesn't work? I run a 9sp Sora short cage mech with an 11-30 cassette and it just about works, the limiting factor being total capacity rather than maximum sprocket size.

The guide wheels on the derailleur were clashing with the teeth on the biggest sprocket, even with the B screw at it's highest tension setting. According to the spec manual, the Tiagra derailleur works with cassettes up to 27 max..

 

[Rasmus]

I made the same change - Tiagra 11-25 to 12-30. My research suggested it should work. Without the chain in the line it looked like the jockey wheel was clashing with the biggest cog, but once I got the chain tension in there it was fine.

 

[Levo-Lon]

The same set up works perfectly on my Tricross - Shimano Tiagra 9 speed shifters with the identical Deore rear derailleur - which is why I went for the same on the Secteur.
I have just been for a 18 mile ride and for some reason it has started working a lot smoother than it was previously. Still not as it should be though, and I tend to be a bit anal about these things , so my quest to get it right continues!

9 speed..my tiagra is 10....
so yes it should work with fine adjustment

had a lot of issues with the wife's 30t and sora..changed to 28 t and worked ok..new bike too

 

[Mo1959]

The guide wheels on the derailleur were clashing with the teeth on the biggest sprocket, even with the B screw at it's highest tension setting. According to the spec manual, the Tiagra derailleur works with cassettes up to 27 max..

That's strange. My Forme has the short cage Tiagra derailleur and it's a 28 tooth. I thought some peeps had even managed to get a 30 to work with a little tweak?

 

[Brandane]

That's strange. My Forme has the short cage Tiagra derailleur and it's a 28 tooth. I thought some peeps had even managed to get a 30 to work with a little tweak?

It is strange. There was a thread recently about the very same subject on compatability, and it was because of that thread that I went ahead with this change to a 30 tooth cassette, thinking the Tiagra medium cage would work fine. It doesn't, and when I later (yes I know I should have checked BEFORE) looked at the Tiagra derailleur spec sheet, it confirmed that it is suitable up to 27 tooth. Ever wish you had just left things as they were? . Once this is sorted, those hills had better be a LOT easier, but I fear the real problem is the engine!

 

[Levo-Lon]

My tiagra is 28t ? It shifts faultlessly.

im assuming you have increased the tension with the B tension screw...
Does seem odd its catching on the cassette

 

[andytheflyer]

Tiagra to deore...you have gone to a different pull ratio.. it will not work properly with your shifter.

Don't think so - I've just fitted a Deore XT Shadow mech and it works fine with my Tiagra STis. All 9 spd.

See https://www.cyclechat.net/threads/audax-gearing-for-giant-defy-advice-pls.184605/

 

[Levo-Lon]

Don't think so - I've just fitted a Deore XT Shadow mech and it works fine with my Tiagra STis. All 9 spd.

See https://www.cyclechat.net/threads/audax-gearing-for-giant-defy-advice-pls.184605/

thought he had got a 10s tig, but 9 ok