Tiagra 4600 rear mech replacement

ra.sk

I run a tiagra 4600 10 spd groupset, 11 -32, with 50-40-30 chainset. The rear mech has always struggled to shift to the smallest ring, the return spring is just not strong enough to pull it over. After a few months it gave up all together. Now, 12 yrs later, it won't go to the second smallest ring either so I'm looking to replace it.
Firstly, has anyone else had this kind of problems with the these rear mechs?
Secondly, what are my options for a replacement mech compatible with this setup? While I'm at it I'm interested in getting something that would let me fit a 34t cassette. An old thread here

http://forums.roadbikereview.com/cyclocross/rear-derailluer-11x36t-rear-cassette-258252.html

Suggests a 9 spd mountain mech could be comptable and allow up to 36t..
Anyone got recommendations?

ugo.santalucia

Tiagra 4600 is unique in its design and pull ratio, so you can't fit a 9 sp MTB derailleur... it would work with any other 10 speed Shimano groupset, but not Tiagra

cryoman1965

ugo.santalucia said:

Tiagra 4600 is unique in its design and pull ratio, so you can't fit a 9 sp MTB derailleur... it would work with any other 10 speed Shimano groupset, but not Tiagra

I was under the impression that the derailleur was used to carry and move the chain up and down the cassette.

The shifter mechanism was what determined the shift ratio and how much cable was being pulled.

So if the derailleur being fitted has sufficient range of movement, and the shifter is compatible with the cassette spacing, would the MTB derailleur not work?

Or have I got this totally wrong?

wongataa

The pull ratio is determined by the geometry of the derailleur mechanism. The shifter just pulls a certain amount of cable per click of the lever.

cryoman1965

wongataa said:

The pull ratio is determined by the geometry of the derailleur mechanism. The shifter just pulls a certain amount of cable per click of the lever.

👍

ugo.santalucia

Yes, as above, the derailleur is a parallelogram, the length ratio of the sides dictates how the cable pull converts into lateral movement... typical 9-10 speed Shimano ratio is 2:1, so 2 mm of cable pull move the derailleur by 4 mm. Tiagra 4600 has a different pull ratio and therefore a different amount of cable pull from the shifters. Don't know why they did it that way, but they might have had a reason

masjer

It's the Tiagra 4700 10 speed that has an 11 speed pull ratio.

The Op's 4600 series shifters are compatible with road 10 speed rear derailleurs (apart from tiagra 4700).
As you've stated, you can use 9 speed MTB rear derailleurs too, which will probably be your best solution.

These are quite cheap.https://bike.shimano.com/en-EU/product/component/acera-m3000/RD-M3000.html

ugo.santalucia

Ooops... I thought 4600 was 9 speed... so yes, all good, you can use a 9 speed MTB derailleur... I did that with a pair of 5700 shifters and it works fine, I was able to use a 36T cassette no probs. I used a shadow XT 9 speed

masjer

ugo.santalucia said:

Ooops... I thought 4600 was 9 speed... so yes, all good, you can use a 9 speed MTB derailleur... I did that with a pair of 5700 shifters and it works fine, I was able to use a 36T cassette no probs. I used a shadow XT 9 speed

I've done similar on a 'winter' bike and it works well. I prefer the shadow design too.

lvquestpaddler

I've got a 4600 Tiagra bike I've just made up for winter but have the Shimano M-592 SGS mech on it and an 11-36 cassette, works brilliant and total capacity is 45T on this mech so you could run your 20T difference front and 25T at the rear with no slackness... in the 30/36 combo

Munsford0

Me too; 4500 (9 speed) Tiagra shifters with an Alivio RD and 11-36 cassette

navrig2

ra.sk said:

I run a tiagra 4600 10 spd groupset, 11 -32, with 50-40-30 chainset. The rear mech has always struggled to shift to the smallest ring, the return spring is just not strong enough to pull it over. After a few months it gave up all together. Now, 12 yrs later, it won't go to the second smallest ring either so I'm looking to replace it.
Firstly, has anyone else had this kind of problems with the these rear mechs?
Secondly, what are my options for a replacement mech compatible with this setup? While I'm at it I'm interested in getting something that would let me fit a 34t cassette. An old thread here

http://forums.roadbikereview.com/cyclocross/rear-derailluer-11x36t-rear-cassette-258252.html

Suggests a 9 spd mountain mech could be comptable and allow up to 36t..
Anyone got recommendations?

I think I have a 9sp MTB RD lying around. Brand new, never been fitted. If you agree to pay postage you can have it and if it works you can donate something to a charity.

IM me direct and I'll see if I can retrieve it from the garage. I'll post a photo once I find it.

navrig2

I have an RD-M571

daniel_b

@navrig2 if this goes unclaimed, I'd be happy to give it a new home, either for my 2006 mtb, or more likely for my 9 year old daughters new road bike to give her a wider cassette range.