Tiagra - Temperamental rear derailleur?

[EasyPeez]

@Yellow Saddle - thanks for your informative post, it's much appreciated and of course it totally makes sense that top end product involves a premium for all the R&D that goes into improving the tech, alongside the better materials.

Smoother and quieter can easily be explained by set-up, cable quality and age, quantity of lubricant on the chain and the wear state of the chain. Al being equal, you won't hear a difference.

As someone who has decided to make some sacrifice in the drivechain area in order to prioritise frame, ride, brakes and aesthetics this comes as music to my ears. I can now pretend I knew this all along when making my decision too, of course
I'm sure I've read plenty of posts on here where people compare different level Shimano and Sram groupsets in terms of their 'smoothness' or 'crispness' or similar. But maybe they're imagining these things. I guess if I spend £2k on a bike next time instead of £1k I'll want to convince myself that my Dura Ace set-up performs better than my Tiagra too, rather than just looks better and weighs less! Thanks again for your insights.

 

[Yellow Saddle]

As usual some pure fantasy mixed in with the otherwise sound sense from Mr Saddle.
New cables don't stretch ?
What brand is that, pray tell?

Like chains, cables don't stretch because we as humans do not have enough strength (or strength amplified by long levers) to stress cable or chains beyond yield. Yield is the point where steel takes on a new length or shape. Yield cannot be achieved by repetitive strain below the yield point. The steel used in brake and gear cables have a sufficiently high yield that the forces we apply to them by pulling the brake lever, do not put them into yield. In other words, they don't stretch from the forces we apply to them.
As for brands, all bicycle chains and cables use a similar steel, cross section and design, so this law of physics is not brand dependent.

I trust that clears up any confusion without too much prayer.

 

[Drago]

My Felt is the latest incarnation of Tiggy band behaves impeccably. Indeed, it's virtually identical to 3 year old 105 on my commuter, such is Shimanos trickle down policy for their annual updates.

And cables do not stretch. The outers compress.

 

[User6179]

Cables don't stretch but someone told me they can bed in at both ends giving the impression they stretch , this sounds more likely and why you might need to readjust new bikes .

Btw the tiagra and 105 look like the same derailleur.

 

[Yellow Saddle]

Cables don't stretch but someone told me they can bed in at both ends giving the impression they stretch , this sounds more likely and why you might need to readjust new bikes .

Not quite. Bedding in at both ends suggests some sort of yield in the steel, which I've explained is not possible, particularly on gear mechanisms where the tension is very, very low.

 

[Yellow Saddle]

Btw the tiagra and 105 look like the same derailleur.

These photos illustrate the point nicely. If I look at the photos carefully, my guess is that the 105 has an aluminium cage (big chamfer) and the Tiagra a steel cage (narrow chamfer). However, this is just a guess.

 

[User6179]

Not quite. Bedding in at both ends suggests some sort of yield in the steel, which I've explained is not possible, particularly on gear mechanisms where the tension is very, very low.

Has some shifters not got plastic where the cable is and would be possible for the cable to bed into the plastic ?

 

[shadow master]

Posters stating there is no difference between the low end and higher end are only half right,because they go on to say the cables are what really make the difference!well if they had ever fitted any of the higher end kit they would know the top stuff is fitted with completely different wires,inner and outer,that's how the shifting is much lighter on ultegra and duraace,people are happy to fit the better bits using 99p non shimano cables and then say they don't work any different to the cheaper kit.

 

[mythste]

As usual some pure fantasy mixed in with the otherwise sound sense from Mr Saddle.
New cables don't stretch ?
What brand is that, pray tell?

Perhaps the cables don't "stretch" - moreover the way the clamps "sit" moves along the cables until they seat more permanently?

Has some shifters not got plastic where the cable is and would be possible for the cable to bed into the plastic ?

And I would have thought there would be some level of bedding as the metal fibres compress together and "bunch" where the clamps clip? I've certainly noticed things "loosening up" over time, what would you attribute this too?

 

[shadow master]

As usual some pure fantasy mixed in with the otherwise sound sense from Mr Saddle.
New cables don't stretch ?
What brand is that, pray tell?

Modern gear inner wires are prestretched and defintley don't stretch, they aren't under any real load,The modern sti outers are linear and don't compress in themselves,the slack inner wire that appears on new bikes after initial riding,is created by outer caps bedding in to the outers and in maybe settling in to the frame lugs!often incorrectly called a stretched wire!

 

[Yellow Saddle]

Has some shifters not got plastic where the cable is and would be possible for the cable to bed into the plastic ?

Also not, all shifters I know of has a metal (usually zinc die-case) cable end receiver. However, even plastics won't yield on gear mechanisms.

I'm kinda delaying the answer because I'm waiting for the peanut gallery to retort. But I'll let the cat out of the bag.

Gear mechanism do go out of tune over time. The reason for this is cable housing wear. Wherever the housing makes a turn, the moving inner cable tends to file and fret away at the soft nylon inner lining and take a shortcut through the corner. It's the exact opposite of a river that erodes the outer radius on the bends. When this happens to a cable, the inner cable becomes relatively longer to the outer cable and the settings go out. However, the cable never stretched.

On brake cables there is sufficient force involved for the inner cable to show signs of wear at those sharp turns. This is visible upon inspection as shiny bits. If you rearrange the little bits of housing on a table, the shiny bits corresponds with the sharp bends, especially the one where the rear brake cable makes a transition from top tube to seat stay.

 

[EasyPeez]

Also not, all shifters I know of has a metal (usually zinc die-case) cable end receiver. However, even plastics won't yield on gear mechanisms.

I'm kinda delaying the answer because I'm waiting for the peanut gallery to retort. But I'll let the cat out of the bag.

Gear mechanism do go out of tune over time. The reason for this is cable housing wear. Wherever the housing makes a turn, the moving inner cable tends to file and fret away at the soft nylon inner lining and take a shortcut through the corner. It's the exact opposite of a river that erodes the outer radius on the bends. When this happens to a cable, the inner cable becomes relatively longer to the outer cable and the settings go out. However, the cable never stretched.

On brake cables there is sufficient force involved for the inner cable to show signs of wear at those sharp turns. This is visible upon inspection as shiny bits. If you rearrange the little bits of housing on a table, the shiny bits corresponds with the sharp bends, especially the one where the rear brake cable makes a transition from top tube to seat stay.

I'm so glad I started this thread now - what an education! Thanks.

 

[Yellow Saddle]

Modern gear inner wires are prestretched and defintley don't stretch, they aren't under any real load,The modern sti outers are linear and don't compress in themselves,the slack inner wire that appears on new bikes after initial riding,is created by outer caps bedding in to the outers and in maybe settling in to the frame lugs!often incorrectly called a stretched wire!

Pre-stretch is also a myth. This gives the impression that steel is soft until it has been stretched. Steel strains perfectly linearly in range before yield. To turn the phrase around (as I've heard before) and say that a "pre-stretch" isn't really a stretch but just a settling in of the winds in the cable is also wrong. For wires wound helically around each other to settle in a different position after a bit of tension would imply that they have yielded (taken on a permanent set), and this is not possible, as I've explained earlier.

 

[shadow master]

@Yellow Saddle - thanks for your informative post, it's much appreciated and of course it totally makes sense that top end product involves a premium for all the R&D that goes into improving the tech, alongside the better materials.


As someone who has decided to make some sacrifice in the drivechain area in order to prioritise frame, ride, brakes and aesthetics this comes as music to my ears. I can now pretend I knew this all along when making my decision too, of course
I'm sure I've read plenty of posts on here where people compare different level Shimano and Sram groupsets in terms of their 'smoothness' or 'crispness' or similar. But maybe they're imagining these things. I guess if I spend £2k on a bike next time instead of £1k I'll want to convince myself that my Dura Ace set-up performs better than my Tiagra too, rather than just looks better and weighs less! Thanks again for your insights.

Another point is Shimano design there systems to be light actioned and smooth as possible!however some of the cable routings used by manufacturers that I've seen lately is poor,particularly on aero models,The felt range suffer with some very compromised shifting due to the twist and turns the wire has to take on its way internally to the rear mech!

 

[the_mikey]

Just my observations:

On my most recent cable installation I used PTFE coated cable, and aside from some adjustments needed after the first 60km of riding the shifting has been entirely reliable over the last two years. A similar installation using plain jagwire cable needed adjustment three times over the same two year period, but I only replaced the inner cables. I find it hard to draw any meaningful conclusions from this, although I may purchase the PTFE coated cable kit next time I overhaul the gear cables.