Chain Wrapping Up On Itself When Changing To The Smallest Chainring: Any Ideas?

[Lovacott]

The protocol (for establishing correct chain length) works for others, so there is something awry (and it isn't Shimano).
Share the cassette range and the chainset tooth numbers, and the chainstay length (BB centre to rear axle centre) and you/we can calculate the chain length needed. Would still like to see an image of the RD from the side with chain in small/small.

Glad that is a candidate 'pearl of wisdom' (upthread) - but I'd just point out that it might seem to work but I suspect you don't know that it works (same with me: as well as that (with new chain and new cassette and all clean) I replaced the worn middle chainring (30,000+km) - chain suck ceased.
"A mitigation I used (and actually have left it there) is a chunky ziptie round the right chainstay up where the chainstay joins the BB shell. The idea was that a chain about to suck would knock against the ziptie and 'un-suck'."
[See the last 'chain suck' thread on here (last month?) https://www.cyclechat.net/threads/p...-when-in-the-small-gears.269738/#post-6228182 ]

I picked up the new rear mech from the Amazon Hub locker about two hours ago and I've fitted it. I checked the chain length with the mech off and it is indeed two links longer than needed to wrap around both large sprockets.

On small to small, there is no sag like I had with the old mech and there is a very noticeable difference in the spring tension. I was also able to adjust B Tension better than I could on the old mech (again, probably a weakened spring).

I've re-indexed and left myself enough barrel adjuster room to either tighten or slacken on the fly on the way to work in the morning.

The chain no longer sucks up when on small to small. I'm going to try and avoid small to small in future but I've left the cable tie in place as a safety measure. Like you, sometimes in the dark, I forget where I am gear wise and when the chain was sucking up yesterday, the cable tie was peeling the chain off and preventing it wrapping.

 

[Lovacott]

As for your scenario, I have never had a problem dropping down the rings, I would stay in the big ring and move up the cassette bit by bit until about halfway then when I need to switch to a smaller ring easy off slightly during the change.

My front change down is a bit on the slow side and if I try to change down on uphill sections, the three seconds or so it takes to swap chainrings loses me all of my momentum. That's why I currently select my front chainring before climbing. There is no noticeable friction resistance in the cable so I can only assume that the front mech spring is a little weak?

I pinched the front and rear mechs off my sons unused bike during lockdown number one. They were exactly the same as on my bike but had only done about 30 miles tops (like most kids today, he's more interested in computer gaming than real life and never really used his bike). Thing is, both mechs were over six years old and if the springs were in their stressed state for that length of time, they would have been knackered.

The new rear mech has worked wonders so I am going to splash out on a new front mech this week.

 

[Ajax Bay]

What are other people's experiences with regard to the springs of older rear derailleurs weakening with age?
I must confess I've not come across this in my bikes and all the bikes I've rescued (bought) from the tip (for family, friends or sale, or parts).

 

[Milkfloat]

What are other people's experiences with regard to the springs of older rear derailleurs weakening with age?
I must confess I've not come across this in my bikes and all the bikes I've rescued (bought) from the tip (for family, friends or sale, or parts).

Never had a problem, even with derailleurs 30 years old.

 

[GoldenLamprey]

What are other people's experiences with regard to the springs of older rear derailleurs weakening with age?
I must confess I've not come across this in my bikes and all the bikes I've rescued (bought) from the tip (for family, friends or sale, or parts).

No, never had an issue either.

 

[Lovacott]

What are other people's experiences with regard to the springs of older rear derailleurs weakening with age?
I must confess I've not come across this in my bikes and all the bikes I've rescued (bought) from the tip (for family, friends or sale, or parts).

Thinking about where we live (on a very steep hill) and the few rides my son did on his bike, the last leg would have been the downhill to home. Just prior to the downhill is a small section of uphill so he would have gone big on the back whilst big on the front and probably stayed there as he turned into our road and coasted home. (I never noted the gear selection when I butchered his bike for parts last April so this is my best guess).

This would have meant that the rear mech spring was maybe left in a stressed position and probably the front as well. The bike hadn't been touched for more than two years which probably didn't help. That said, it's all been working fine up until the last week (apart from slow changes down on the front).

If you stress a spring for long enough, "elastic fatigue" sets in and the spring becomes almost useless.

That said, my groupset is only entry level Shimano Tourney stuff so I suppose you get what you pay for?

 

[GoldenLamprey]

Thinking about where we live (on a very steep hill) and the few rides my son did on his bike, the last leg would have been the downhill to home. Just prior to the downhill is a small section of uphill so he would have gone big on the back whilst big on the front and probably stayed there as he turned into our road and coasted home. (I never noted the gear selection when I butchered his bike for parts last April so this is my best guess).

This would have meant that the rear mech spring was maybe left in a stressed position and probably the front as well. The bike hadn't been touched for more than two years which probably didn't help. That said, it's all been working fine up until the last week (apart from slow changes down on the front).

If you stress a spring for long enough, "elastic fatigue" sets in and the spring becomes almost useless.

That said, my groupset is only entry level Shimano Tourney stuff so I suppose you get what you pay for?

I speak from a position of no knowledge whatsoever, but I'd be amazed if the springs on a mass-market bike were not sufficient to withstand decades of normal use.

 

[Ajax Bay]

If you stress a spring for long enough, "elastic fatigue" sets in and the spring becomes almost useless.

Care to offer a reference for that? It might seem so intuitively, to you, but not familiar with that phenomenon.
If anything the cheaper RD springs will be heavier and, intuitively, more robust.
Your new RD looks great (from the images). Never seen a Tourney that new.

 

[Ming the Merciless]

My oldest 12 year old rear derailleur with over 100,000 miles of gear changes is doing just fine.

 

[Lovacott]

I speak from a position of no knowledge whatsoever, but I'd be amazed if the springs on a mass-market bike were not sufficient to withstand decades of normal use.

Any spring stored in a stressed position will lose its spring over time. Entry level mechs will use a lower grade of material to keep costs down so it's hardly a surprise.

Mass market bikes like my Apollo are designed to look good in the shop to be bought by people who might use them a couple of times a year when they go on holiday to Norfolk. A £200 imported bike is not going to have a £150 groupset.

My bike was virtually useless after around a month of commuting (500 miles). Bottom Bracket bearings were shafted, pedals were split, the front mech grip shifter literally shattered during a change and the wheel bearings made a nasty crunching noise.

My freewheel was tagged "Shimano" but wasn't actually made by Shimano. It was a sub contact under licence make (I can't remember the factory name, but it was French and was stamped on the retaining ring).

Although I don't buy high end components, I avoid the cheapest. I could have replaced my rear mech with one for £8.99 but went for the £17.99 one instead. Same goes for the Freewheel, crankset and chain.

I had a half decent Raleigh racer in the 1990's and I did over 150 miles a week on it commuting and never replaced anything gear related on it. Just cleaned and oiled it now and again.

 

[Lovacott]

Care to offer a reference for that? It might seem so intuitively, to you, but not familiar with that phenomenon.

https://dl.asminternational.org/han...54/Fatigue-of-Springs?redirectedFrom=fulltext

Any spring which stays stressed for long periods will lose spring tension. The same applies if the spring is used an excessive number of times. Think "old mattress".

My old rear mech did fold back on itself when I removed it, but it took no effort at all to push against the spring to open it back up again. The new rear mech offered up a fair bit more resistance. I have no droop in the chain when on small to small where yesterday it was very noticeable. Also, the new rear mech changes down a lot more quickly which suggests that the selection spring on the old one was also a bit weak.

 

[davidphilips]

Never had a problem with derailleur springs losing tension but have had issues with rear derailleurs on bikes that are used through winter and bad weather where the pivot (the one that allows the rear derailleur to move back and forward not side to side) gum up with dirt, bit time consuming taking derailleur off and stripping and cleaning.

 

[Ajax Bay]

Your link seems paywalled.
How about this (bit of editing):
"properties that are are of great interest for springs it is the creep/relaxation and the fatigue.
"A physical phenomenon with certain metals is that at stress below the yield strength of the material a very slow plastic deformation take place. In the spring branch this is called ‘creep’. "How much creep occurs depends on the temperature, the stress in the metal and/or the metal's yield strength and the time. For example, increased temperature, stress and time also increase the creep/relaxation."
[Comment: If a spring is kept under constant stress there will be some creep (relaxation) but its magnitude is limited (see graph).]

"Also with metals, a cyclical stress below the yield strength of the spring material can cause break or fatigue to occur. The problem of fatigue starts with the development of a micro fatigue crack which grows for every pulsation. When the stress in the remaining material reaches the ultimate tensile strength the spring will break. The risk of spring fatigue depends on other factors too, such as the designed stress in the spring, alongside the amplitude of the pulsation and the material’s maximum tensile strength."

[Comment: Fatigue is what spokes finally succumb to, for example.]

 

[GoldenLamprey]

Any spring stored in a stressed position will lose its spring over time. Entry level mechs will use a lower grade of material to keep costs down so it's hardly a surprise.

Mass market bikes like my Apollo are designed to look good in the shop to be bought by people who might use them a couple of times a year when they go on holiday to Norfolk. A £200 imported bike is not going to have a £150 groupset.

My bike was virtually useless after around a month of commuting (500 miles). Bottom Bracket bearings were shafted, pedals were split, the front mech grip shifter literally shattered during a change and the wheel bearings made a nasty crunching noise.

My freewheel was tagged "Shimano" but wasn't actually made by Shimano. It was a sub contact under licence make (I can't remember the factory name, but it was French and was stamped on the retaining ring).

Although I don't buy high end components, I avoid the cheapest. I could have replaced my rear mech with one for £8.99 but went for the £17.99 one instead. Same goes for the Freewheel, crankset and chain.

I had a half decent Raleigh racer in the 1990's and I did over 150 miles a week on it commuting and never replaced anything gear related on it. Just cleaned and oiled it now and again.

Intellectually, I absolutely get what you are saying. Practically, I just don't think it makes a significant difference.

 

[Lovacott]

Intellectually, I absolutely get what you are saying. Practically, I just don't think it makes a significant difference.

There was significant slack in the chain when on small to small which the new mech has taken out and the strength of the spring is very much greater on the new mech.