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Old 04-07-11, 06:56 AM   #1
RI_Swamp_Yankee
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Do higher-end derailleurs hold their settings better?

I have bog-stock Tourney derailleurs on a 21-speed, MTB-geared pedal-forward bike (an Electra) - the FD is top-swing, bottom-pull. They're combined with the SiS 7-speed indexed thumb shifters. The bike is an everyday, all-weather city commuter.

The derailleurs always seem to be going out of adjustment (tho it's better with the new shifters) - would upgrading the derailleurs help, or is this just how it's going to be with a bike that has such a long chain? Would one derailleur going out of adjustment affect the other? Do higher-end derailleurs hold their settings better, or are they just lighter/more durable?

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Old 04-07-11, 07:09 AM   #2
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Derailleurs are pretty simple mechanisms. As long as the cable anchor and barrel adjusters are holding cable tension, a lower end derailleur should hold setting as well as higher end one. If your shifting is going out of adjustment regularly, you are losing cable tension for some reason. It could be a derailleur issue, (cable slip at anchor bolt or adjuster problem) but the problem could be elsewhere.
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Old 04-07-11, 07:25 AM   #3
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+1, even the cheapest derailleurs have limit screws and cable adjusters that stay put. If you're having problems with keeping adjustments look elsewhere.

It also helps to keep track of which way you need to keep re-adjusting.

* If it's back and forth, it could be stickiness in the cables, or shift mechanism, or possibly a bent
hanger, making any decent adjustment impossible.

* If you're always turning the cable adjuster out to tighten the cable, something is slipping. Cables don't stretch until they're frayed and about to break, though there often is some settling of newly replaced housings.

* If you're always turning the adjuster in to loosen the cable, that could be more serious. Since there's no way the cable would magically get tighter, the likeliest problem is that your RD hanger is getting bent inward. Adjusting the cable is only part of the solution, you also need to adjust the inner and outer limits, especially the inner lest the chain over-shifts into the spokes.

If you take the time to analyze the reasons your derailleur won't stay adjusted, you should be able to correct any underlying cause and adjust it once have it stay that way for months.
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Old 04-07-11, 08:00 AM   #4
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Originally Posted by RI_Swamp_Yankee View Post
I have bog-stock Tourney derailleurs on a 21-speed, MTB-geared pedal-forward bike (an Electra) - the FD is top-swing, bottom-pull. They're combined with the SiS 7-speed indexed thumb shifters. The bike is an everyday, all-weather city commuter.

The derailleurs always seem to be going out of adjustment (tho it's better with the new shifters) - would upgrading the derailleurs help, or is this just how it's going to be with a bike that has such a long chain? Would one derailleur going out of adjustment affect the other? Do higher-end derailleurs hold their settings better, or are they just lighter/more durable?
The derailer is a dumb device. It is merely a robot that does what the shifter tells it to do. All derailers, from the most expensive to the cheapest, will go out of adjustment because the cables are stretching with use. Some will say that cables don't "stretch" but even prestretched cables are still elastic. For example, a 1.1mm derailer cable of 60" length with 10 lb of force on it will stretch almost a millimeter in length. That's enough to throw off the rather close tolerances that the shifter must operate in. Cable housing plays a role too. Eventually you do reach a point where every thing settles in...sort of...and you don't have to adjust much. You still have to occasionally adjust but just not as often.

More expensive derailers are just lighter and perhaps a little smoother in operation.
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Old 04-07-11, 08:12 AM   #5
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Some will say that cables don't "stretch" but even prestretched cables are still elastic. For example, a 1.1mm derailer cable of 60" length with 10 lb of force on it will stretch almost a millimeter in length. .
With all due respect, and I mean that sincerely, this is a bit of sloppy analysis well beneath you.

Yes, a cable does stretch under tension, but that happened the moment it was tensioned the first time, and the RD adjusted accordingly. Unless you somehow manage to adjust trim with the tension released, the tension based stretch is calibrated in and doesn't change. It wouldn't be different at a later time unless the cable was stretched beyond it's elastic limited and permanently distorted (not likely), or the RDs spring constant changed (even less likely).

Until then the tension based stretch won't change over time any more than a correctly calibrated bathroom scale would change it's readings from day to day.

BTW- As I said in my prior post, the cable will begin to stretch near the end of it's life as it frays and gets ready to fail completely. Consider this late stage stretch a warning sign and have the replacement handy.
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Old 04-07-11, 08:36 AM   #6
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+2 that even the least expensive derailers hold their positions. It's not a problem with the Tourney components.

Which adjustments are moving on you? Limit stops? Cable tension? Something is probably just loose somewhere.
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Old 04-07-11, 08:47 AM   #7
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The Sram 3 that came on my Rans Stratus worked for a year without needing re-adjustment. I did replace it with a Sram 7 since it was more serviceable. I agree with the poster that say that if constant re-adjustment is needed, there is a problem. Derailers are just a mechanical device therefore it is a black and wihite situation.
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Old 04-07-11, 08:50 AM   #8
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Basically derailers just get ligher the more money you pay. The geometry is pretty much the same on any one brand. Best advice a middle cost derailer probably get you the most bang for the buck.
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Old 04-07-11, 08:52 AM   #9
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RD Settings are 3 ..2 limit screws and the B screw a position around the mounting bolt preload..

Once you have the adjustment determined, you can use thread lock compound on all 3.

If its shifting that troubles you on index stuff, you're not alone..
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Old 04-07-11, 08:53 AM   #10
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Would be checking chain, cassette, cables and pulleys & derailler alighment before looking to change the derailler, as all of these can affect it
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Old 04-07-11, 09:21 AM   #11
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Cable tension, I'm guessing - up front, it gets balky going into bigger rings under any or no load, will hop off completely going into the granny gear under moderate load, and the chain will rub against the derailleur (most common). I'm always fiddling with the barrel adjuster on the shifter to fix it, and the H-stop is almost backed out of the mechanism all the way. I'm careful not to cross up my chainlines with gear selection, so it's not a matter of using the hyper-range cog in the big ring.

Out back, it doesn't like shifting up or down in gears 6-3. It's generally a game of "which way am I turning the barrel =this= time!"
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Old 04-07-11, 09:33 AM   #12
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Cable tension, I'm guessing - up front, it gets balky going into bigger rings under any or no load, will hop off completely going into the granny gear under moderate load, and the chain will rub against the derailleur (most common). I'm always fiddling with the barrel adjuster on the shifter to fix it, and the H-stop is almost backed out of the mechanism all the way. I'm careful not to cross up my chainlines with gear selection, so it's not a matter of using the hyper-range cog in the big ring.

Out back, it doesn't like shifting up or down in gears 6-3. It's generally a game of "which way am I turning the barrel =this= time!"
The rear screams of sticky cables or a bent hanger. But it could be a mis-match of components, or a sticky lever. If the RD is old it could also be worn pivots in the pantograph.

The FD probably just needs a thorough re-adjustment, starting with the mounting position, to the limits to trim. Read a few (not just one) of the various tutorials until you have a clear sense of how to set up an FD and rework it from scratch. Be aware that if you have index front, you won't be able to trim the FD while riding, so you need to trim it for best chain clearance in the gear combinations you actually ride in.
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Old 04-07-11, 03:04 PM   #13
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With all due respect, and I mean that sincerely, this is a bit of sloppy analysis well beneath you.

Yes, a cable does stretch under tension, but that happened the moment it was tensioned the first time, and the RD adjusted accordingly. Unless you somehow manage to adjust trim with the tension released, the tension based stretch is calibrated in and doesn't change. It wouldn't be different at a later time unless the cable was stretched beyond it's elastic limited and permanently distorted (not likely), or the RDs spring constant changed (even less likely).

Until then the tension based stretch won't change over time any more than a correctly calibrated bathroom scale would change it's readings from day to day.

BTW- As I said in my prior post, the cable will begin to stretch near the end of it's life as it frays and gets ready to fail completely. Consider this late stage stretch a warning sign and have the replacement handy.
Not according the the displacement calculator I used.

[QUOTE]Two kinds of stretch occur in cable based on wire rope: constructional stretch and elastic stretch. This stretch is due to two different causes.

1. Constructional Stretch - When cable is made, the load at the closing head is light. Therefore, there are small clearances between the wires and strands, and between the strand and the core. The application of initial load causes wires and strands to seat properly and a slight overall elongation of the strand or cable accompanies this section. The amount of constructional stretch is not constant for all cables - it depends on such variables as type of construction, length of lay, and other factors, including the load applied.

2. Elastic Stretch - Elastic stretch is the actual elongation of the wires of a strand or a cable. This is caused by the application of a load up to the yield point of the metal. The stretch is approximately proportional to the load applied. When the load is released, cable subjected to elastic stretch returns to its approximate original length, providing the stretch has not reached the yield point of the metal.[QUOTE]

Elastic stretch is always there. I suspect that bicycle cable stretch is due to 3 factors. First there is the construction stretch which is mostly taken care of during the prestretching of the cable by the manufacturer. Not completely but mostly. There is probably still some construction stretch in there that would allow the cable to lengthen slightly when new. This is the reason for some of the need for adjustment for new cables.

Second is the elastic stretch. I don't know what the yield strength of derailer cables is but I suspect that is is rather low. And if you are going past the yield strength, the wires themselves will stretch. If the magnitude over the yield limit is small, the effects could be cumulative so that the cable stretches over time...as you see with most derailer systems. I also suspect that you reach a limit where the elastic stretch yield limit as been surpassed and it simply won't stretch much more. This is borne out by the fact that old cables eventually need less adjustment.

The last, and I think the least important, is the cable housing. While it is easy to stretch cables and wires, it's very difficult to compress it. If the cable housing is new, the settling in of the housing could have a slight effect but new cables with old housing still has the problem of the derailers going out of adjustment. New cable housing and old cables seldom cause problems in my experience. This is likely due to the elastic stretch and construction stretch of the cables having been taken care of by the prior use.
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Old 04-07-11, 03:34 PM   #14
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cable tension, i'm guessing - up front, it gets balky going into bigger rings under any or no load, will hop off completely going into the granny gear under moderate load, and the chain will rub against the derailleur (most common). I'm always fiddling with the barrel adjuster on the shifter to fix it, and the h-stop is almost backed out of the mechanism all the way. I'm careful not to cross up my chainlines with gear selection, so it's not a matter of using the hyper-range cog in the big ring.

Out back, it doesn't like shifting up or down in gears 6-3. It's generally a game of "which way am i turning the barrel =this= time!"
AAAAAAAAARRRRRRRRRGGGGGGGGG!!!! DO NOT FIDDLE WITH THE LIMIT SCREWS!

I swear that limit screws are to bicyclists what frozen poles are to little kids! Must...touch...the...limit...screw.



<calming thought, calming thoughts>

You say that the front derailer rubs the chain. Without you saying which, I suspect that it's the outer plate when the chain is in the large ring. This means that the derailer isn't moving far enough outboard. The fact that the front is balky also means that the cable isn't moving the cage far enough outboard. The issue isn't limit screws <calming thoughts> It's that the cable is stretched and isn't moving the cage far enough outboard because the shifter can't move it far enough. The low end dropping the chain may actually be due to the limit screw...DON'T TOUCH IT YET!

Shift the bike into the lowest gear on the front. Make sure the shifter has released the cable entirely. Check to see if the cable has any slack in it. It should be taut, not tight. If you can pull it more away from the frame more than a little without moving the derailer, it's too loose. You might need to detach the anchor bolt and pull up the slack but try the barrel adjuster first.

Once you have the cable taut but not tight, try shifting to the large ring. If the cable is tight enough, you'll probably throw the chain off to the outside now because YOU FIDDLED WITH THE LIMIT SCREW <calming thoughts>

But all is not lost. With the bike in the highest gear on the back, adjust the high limit screw so that the outer plate is just not touching the chain. Yes, I just told you that you get to fiddle with it now. Enjoy it because once you get it set, I don't want you to touch it again!

Now shift the rear to about mid-range. Shift the front to the inner. When the chain shifts onto the inner ring, the derailer should be almost centered over the chain wheel. It may be slightly inboard. You don't want it to move too far inboard because that causes the drop but you don't want it too far outboard either because it won't shift. If it's too far inboard, you can fiddle with the low limit screw until it shifts but doesn't drop the chain. Small increments.

After you got this all done, I want to imagine a welding torch. You are going t weld those limit screws in place (in your mind) and then NEVER TOUCH THE DAMNED THINGS AGAIN

For the rear...I'm writing a damned book here...shift the derailer up to the highest gear (smallest cog) check the cable tension like before and make adjustments if needed. While pedaling, shift the rear shifter one click. If properly tensioned, the chain should hop up to the next gear and be centered over the cog. If it doesn't hop up immediately, tighten the cable housing just a little while pedaling. When the chain hops up to the next cog, stop tightening!

If the chain hops up to the next gear but it clatters, the cable is too tight and the chain is hitting the next cog in the cassette. You can loosen the cable just a little while pedaling until the noise goes away.

Now, with pedaling, shift the chain to cog #3. It should be silent and it should do it quickly. If it doesn't move tighten the cable in quarter turn increments while until it makes the shift. If it clattering, loosen the cable in the same increment until the noise just goes away. That should do it. Check it again and readjust in small amounts if needed. No, you don't get to fiddle with the limit screw
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Old 04-07-11, 04:40 PM   #15
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......
...Two kinds of stretch occur in cable based on wire rope: constructional stretch and elastic stretch. This stretch is due to two different causes.

1. Constructional Stretch -.....

2. Elastic Stretch - .....
I shortened the quote to save space, read it in the original a few posts up.

This is my favorite kind of post, because while it's 100% correct in the absolute sense, it manages to be utter and complete nonsense at the same time. That's because it's out of context, dealing with effects that are too small to matter in the real world.

First constructional stretch. This is higher in wire ropes made of the 7x7 or 7x19, etc. type of construction where the strands themselves are cables, as opposed to the 1x7, 1x19 etc. types made of wound mono-filaments as are typical gear and brake inner wires. Also decent inner wires are die drawn which takes out almost all the constructional stretch. Lastly whatever constructional stretch is left over is quickly taken up early on after installation.

We can debate whether housings stretch, housings compress, ferrules settle, frames shrink, or whatever, but it doesn't matter, because we all know that there's a short break in period which results in a slight change of trim as if the cable stretched.

Now the elastic stretch. While gear inner wires don't have very high yields strengths, they are high enough to dwarf the actual operating loads, which are limited by the RD return spring, and/or the rider's strength in one finger or thumb (multiplied by the leverage factor of the shift lever).

Gear wires are never subjected to forces (in normal, and non-exteme not normal use) anywhere near their yields. If they were, folks would be re-trimming their derailleurs all the time, and always in the same direction. Give the engineers at Shimano et al, a bit of credit. They wouldn't spec gear wires which operate near yield strength.

I'm not saying that it isn't possible to stretch a gear wire if you forced the lever with all your hand strength, but that's about what would take. And that's if it doesn't slip in the pinch bolt first.

In any case, the OP has problems with trim changing in both directions on a system he's had for a while. That makes any discussion of both kinds of stretch moot, the first based on the time factor, the second because they wouldn't shrink back.

In the bike world we often make technical statements which are not 100% accurate, but become so with an implied "to a material degree". For example we all say chains don't stretch, but appear to because of wear. That isn't precisely true, a chain like anything else stretches under tension, but it isn't by an amount that matters for the discussion given the working loads, making the original statement true in context.

So for all practical purposes, it's accurate to say that inner wires don't stretch. (the "in normal working conditions" is implied)
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Old 04-08-11, 09:04 AM   #16
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This is my favorite kind of post, because while it's 100% correct in the absolute sense, it manages to be utter and complete nonsense at the same time. That's because it's out of context, dealing with effects that are too small to matter in the real world.
Bicycle cable stretch. That is a given. If they didn't bicycles wouldn't need mechanisms to take cable stretch into account, i.e. barrel adjusters. Cables stretch more when the are new...another given. A 1.1mm cable isn't all that thick and as I showed with the displacement calculator a force of 10 lb...not really all that much and pretty easy to accomplish with one finger...can stretch the cable nearly a full millimeter.

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First constructional stretch. This is higher in wire ropes made of the 7x7 or 7x19, etc. type of construction where the strands themselves are cables, as opposed to the 1x7, 1x19 etc. types made of wound mono-filaments as are typical gear and brake inner wires. Also decent inner wires are die drawn which takes out almost all the constructional stretch. Lastly whatever constructional stretch is left over is quickly taken up early on after installation.
Construction stretch would be higher in wire ropes because each strand is made of smaller strands that themselves have construction stretch and those strands may be made of even smaller strands that have their own construction stretch. I suspect that the result isn't just additive but multiplicative.

That, however, doesn't mean that the smaller strands nor cables like those used for derailer cables don't have construction stretch in them. They are prestretched during manufacturing to remove some of the construction stretch but I doubt that it's all removed.

Then there is the effect of manufacturing the bicycle cables themselves. I doubt that each bicycle cable is prestretched. Jagwire and other companies that make bicycle cables buy the cable on spools that are prestretched, probably during the spooling process. There's variability in that process and the very inner part of the cable near the arbor of the spool is going to see a different environment than the cable near the outer part of the spool. This will have more of an effect later in the process.

Jagwire takes the cable off the spool and straightens it. This adds some construction stretch back into the cable since it relaxes the cable that was wound around the arbor. The cable nearer than arbor...depending on the diameter of the arbor...is going to be more tightly wound and thus may relax more during the unspooling process. This will add back even more construction stretch.

The cables are then cut into lengths, let's say about 8 feet and ends are swagged onto the cable. Perhaps both ends. Cutting the cable will relax the cables even more, again adding back stretch.

Then the small cables are coiled. The process of coiling will relax the cable further and add more stretch. With all this going on, I'm amazed that the cable isn't just a pile of wires on a shop floor somewhere

And all this happens before the consumer get the product and does his magic of unwinding a relatively short cable, forcing it through the housing, cutting it and then putting tension on it. The cable has been tensioned and untensioned so many times by the time that you run it through a derailer/shifter that the individual strands are going to have to reorient and rebed.

And that's even before you start tensioning and detensioning the cable while shifting.

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Originally Posted by FBinNY View Post
We can debate whether housings stretch, housings compress, ferrules settle, frames shrink, or whatever, but it doesn't matter, because we all know that there's a short break in period which results in a slight change of trim as if the cable stretched.
Yup. And the reason you have a break in period is because all of the stuff that done to the cable before you have it in your hands.

Try using an old compressionless cable housing with a new cable and see how much stretch you have to take up after a few rides. Try an old cable with new compressionless housing. I doubt that you'll have to retrim much at all in the latter case.

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Originally Posted by FBinNY View Post
Now the elastic stretch. While gear inner wires don't have very high yields strengths, they are high enough to dwarf the actual operating loads, which are limited by the RD return spring, and/or the rider's strength in one finger or thumb (multiplied by the leverage factor of the shift lever).

Gear wires are never subjected to forces (in normal, and non-exteme not normal use) anywhere near their yields. If they were, folks would be re-trimming their derailleurs all the time, and always in the same direction. Give the engineers at Shimano et al, a bit of credit. They wouldn't spec gear wires which operate near yield strength.
The return spring on a derailer has nothing, or at least very little, to do with the force put on the cable. Almost all the force comes from the rider's hands.

The overall cable may have a very high yield strength but the individual strands don't. If the strands are loose in the cable and the cable has to rebed, you are working on individual strands to a certain extent and each one is going to yield just a little each time force is put on it until all the strands are bedded and working together. Once bedded, the individual strands are going to work together better and stop stretching as much and make the need to retrim less frequent.

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Originally Posted by FBinNY View Post
I'm not saying that it isn't possible to stretch a gear wire if you forced the lever with all your hand strength, but that's about what would take. And that's if it doesn't slip in the pinch bolt first.
Back in the days of thumb shifters...when men were men and mountain bikers had thumbs that Nintendo players envied...you had to put all most that much force on the shifter to make the shift. Retriming for index shifting was much more frequent because you stretched even well bedded cables more. It's also where I learned the necessity of a well tightened pinch bolt

Today's shifters (and derailers) require much less force for the shift. That's also evidenced by a lessened need to retrim derailers. Most of the time, except for the first 100 to 200 miles, you don't have to mess with the derailers. You still have to initially because of the stretch in new cables but it is less.

Quote:
Originally Posted by FBinNY View Post
In any case, the OP has problems with trim changing in both directions on a system he's had for a while. That makes any discussion of both kinds of stretch moot, the first based on the time factor, the second because they wouldn't shrink back.
I've experienced exactly the kind of issue that RI_Swamp_Yankee is talking about. The bike won't shift easily to the highest gear and it drops off on the inner gear. It always comes back to a stretched cable...and, just perhaps, an improperly adjusted lower limit screw...Don't touch it

First the cable is too long to force the derailer far enough outboard to move the chain up to the outer ring easily or at all. Then the lower limit screw puts the derailer just a little to far inboard because the initial installation of the cable resulted in a cable that was a little tight. To get the bike to shift to the low range under load, the mechanic may have moved that inner screw just a little inboard. But the cable was tight enough to keep the front derailer from coming to the stop and held the chain just a little out from dead bottom.

Once the cable is stretched enough after the initial installation, the cable can't move the derailer and chain out far enough but allows the derailer to hit the lower stop and derails the chain completely to the inside. It doesn't help matters any that shifting to the very inner ring is usually done under power and the chain thus has lots of momentum when traveling inboard. It's very easy to overshot that inner ring and, once overshoot occurs, there's little you can do to get the chain back on without stopping.

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Originally Posted by FBinNY View Post
In the bike world we often make technical statements which are not 100% accurate, but become so with an implied "to a material degree". For example we all say chains don't stretch, but appear to because of wear. That isn't precisely true, a chain like anything else stretches under tension, but it isn't by an amount that matters for the discussion given the working loads, making the original statement true in context.

So for all practical purposes, it's accurate to say that inner wires don't stretch. (the "in normal working conditions" is implied)
Yep. Chains don't 'stretch'. They wear and elongate.

Cable housing may bed in a little but the amount is minimal because it's very difficult to compress wire.

Inner wire cables, on the other hand, elongate. If you elongate something by putting tension on it that, by definition, is stretching. Whatever mechanism is at work, the cable is still gaining length and, again, that is stretching. It may only happen for a short period of time but it is still stretching. There's no other word for it.
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Old 04-08-11, 09:10 AM   #17
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There's no point in debating this farther.

You've expressed your opinion, and I mine.

Readers can draw their own conclusions based on the info offered, and their own experience.
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Old 04-08-11, 10:07 AM   #18
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When I set up bikes it is very rare that I have to go back and fine tune the derailleurs because of stretch / bedding in as there are two factors at work here and different cables have different properties... stainless has different physical characteristics and I have found that it is more prone to breakage than steel cable. It is a harder material and thus, is more brittle so any defect in a strand of wire will compromise the cable.

Properly finished cable ends and good quality cable means that once the bike is set up there will be little or no adjustment required while lower end cable tends to be more prone to some additional stretch.

After the bike is set up I run back and forth through the gears to set the cable and ends and it only takes a few shifting cycles to have everything bedded in.

People obsess over cable and in reality, the uber expensive stuff does not work that much better than regular steel cable and the secret for good shifting is in the cable housing as better housing allows for smoother cable motion because of reduced friction.
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Old 04-08-11, 05:36 PM   #19
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After shucking another chain trying to go into the granny gear, I took a good look at the front derailleur. I think the problem is two-fold - first, the side-to-side angle it was mounted at needed fine tuning, and the cable re-attached and tighened once that was accomplished. Secondly, the H-stop does need to be unscrewed all the way. The bike doesn't have a vertical seat-tube, it has a small tube welded to the top of the BB, and a really cheap top-swing derailleur attached. It doesn't quite have the range to accomodate three rings comfortably, and the crank is pretty cheap, too - the spindle seems too wide for the bracket, and the large and middle rings are already somewhat warped, making things even dicier. So, I need to look into new rings or even a new crankset, and maybe a new FD if I can find one with a wider range of adjustment.

Once the FD was sorted out (on the side of the road, thank goodness for double-legger kickstands), the RD came right in line with a half-turn of the adjuster barrel, as advertised.

Thanks, all!
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