Bicycle Mechanics - Prestretched Chain

I was told that Shimano "prestretches" new 10 speed chains. Can someone explain the hows and whys of this?

Who told you this?

Chains don't stretch, they wear. If Shimano's marketing a pre-stretched chain, then I'm sitting on a gold mine of pre-enjoyed units.

Who told you this?

I was told by a young kid at a bike shop in the next county over. A friend of mine also said that when he bought his new Specialized Allez, that the LBS "prestretched" his chain along with the cables.

So... They went for a test ride and then slammed on all the brakes? Then adjusted it again?

Sounds fishy at best. Chain strech occurs when the holes at the pin/plate junctions elongate due to normal wear. I imagine that one could suspend hundreds if not thousands of pounds of static weight from a bicycle chain and it would not stretch.

I was told by a young kid at a bike shop in the next county over. A friend of mine also said that when he bought his new Specialized Allez, that the LBS "prestretched" his chain along with the cables.

Sounds like they're repeating something they thought they heard someone else say. Or have been "hung" by the other more experienced guys. Sort of like sending a new wrench-in-training to the hardware store for elliptical ball bearings that go in worn out hubs. Or to look in the QBP catalog for transparent seatpost clamps or whatever.

Cables don't stretch, either, but housings compress, giving the illusion the cable got longer. Don't believe it? On a bike with well used housings, take a brand new derailleur cable and run it through the old housing and adjust the derailleur. Now go ride and note how it stays adjusted! The housings were already fully compressed. All major brands of cables are prestretched in a controlled fashion at the factory. No need in the shop. But we always compress the housings!

Uh, what possible function would pre-stretching a chain accomplish?

Uh, what possible function would pre-stretching a chain accomplish?
Maybe it keeps the chain from shrinking and compressing the cogs and chain rings, causing deformation in those parts? ;)



If the winking icon is not enough to alert you, I am KIDDING!

Would using a pre-stretched chain require you have matching pre-stretched cogs & chainrings? ;)

When I worked for a LBS, we had a nifty device that stretched cables for you. That helps avoid the normal 1 week tune-up when everything settles in. As for a chain, I've never heard of such a thing. And if there is, I have a chain just about prestretched for Campy to start marketing. :D

to look in the QBP catalog for transparent seatpost clamps
:lol: :roflmao: :lol:

Had not heard that before. Funny!

This is complete bullcrap anyways. First of all the term is wrong, "stretch". Second what really amounts to stretch is chain wear.

So in effect what they're saying is, they'll "strecth" the chain for you which means they'll give you an old chain. What a load of crap.

Sounds like they're repeating something they thought they heard someone else say. Or have been "hung" by the other more experienced guys. Sort of like sending a new wrench-in-training to the hardware store for elliptical ball bearings that go in worn out hubs. Or to look in the QBP catalog for transparent seatpost clamps or whatever.

When I worked at a hardware store, this frequent customer would come in, pick out the newbies, and ask for a left-handed monkey wrench or elbow grease. Most of them just asked me if we carry them (to which I just laugh) but a few people actually looked up their little store guide and pointed the guy in the direction of tools or lubricants!

Sounds like my auto parts/tools shopping list...

Head stud stretcher
Cross-drilled brake lines
Blinker fluid
Heavy-duty tire beads
Left-handed screwdriver
Muffler bearings
Elbow Grease

Whats next, pre worn tires?
Al

Cables don't stretch, either, but housings compress, giving the illusion the cable got longer. Don't believe it? On a bike with well used housings, take a brand new derailleur cable and run it through the old housing and adjust the derailleur. Now go ride and note how it stays adjusted! The housings were already fully compressed. All major brands of cables are prestretched in a controlled fashion at the factory. No need in the shop. But we always compress the housings!

This is not quite right either. In fact what happens is that the cable wears its path into the liner inside the housing. On a new bike, the cable wears a groove into the metal that it runs over. Grabbing the brake levers hard after installing new cables take up the slack that may exist in the run from lever to brake, and permits the cable to "slot" into the old wear pattens.

I'm also interested in seeing a "cable stretcher". It must suspend from the ceiling so someone can dangle off the end of the cable... because I can't see a cable ever stretching otherwise. Go figure it -- test the amount of force required to move a derailleur or engage a brake caliper. Then go attach the end of a cable to something immoveable, and try to "stretch" it. Good luck. Now if that poster had said "a tool for taking up the slack in a cable system" then I might believe him.

Anyone who says a chain or cable used on a bicycle is stretched, is playing with themselves. The key for the OP was "I was told by a young kid at a bike shop".

Pre-chewed gum? Re-fried Beans? Pre-stretched Chains? What is this world coming to? What will they sell next? Used panties? Pre-enjoyed Condoms?!?

gah.

This is not quite right either. In fact what happens is that the cable wears its path into the liner inside the housing. On a new bike, the cable wears a groove into the metal that it runs over. Grabbing the brake levers hard after installing new cables take up the slack that may exist in the run from lever to brake, and permits the cable to "slot" into the old wear pattens.

What metal is having a groove worn into it?:eek: I've put on thousands of cables and have never seen these grooves. In any cable run, metal on metal is not good! Once the cable wears into the inner liner, it's time for new housing!

I had the LBS pre ride my bike for me. I got in 2500 miles this year and only rode it for 30 minutes!

What metal is having a groove worn into it?:eek:

You really have to be old school to remember that cable housing used to be unlined, and allowed metal to metal contact.

What metal is having a groove worn into it?:eek: I've put on thousands of cables and have never seen these grooves. In any cable run, metal on metal is not good! Once the cable wears into the inner liner, it's time for new housing!
I bow to your superior experience.

But, as I do so, I should point out that I don't think all brake cable outers have a plastic lining. Just a mo, I will go and check on one of the bikes out in the garage... nope, no liner there on the housing. What about canti brakes... no metal to metal contact there? What about where the barrel or mushroom end goes... oh yes, I see that there on my bike, too. There's also a bike out there with ... wait for it... a travel agent with metal-to-metal contact between the cable and the pulley. That's without the straddle fitting for canti brakes where there is... wait for it, metal to metal contact!!

Just occasionally, if you choose to work on bikes that may not be the current fashion trend, you might find cables running through a tube or two above the BB to the front and rear derailleurs... let me see on the (admittedly old frame up on the wall, a Maruishi)... yes! Metal to metal contact through one of those tubes!

And, if you look at Sheldon Brown's little tweak for 9 speed shifters converting to 10-speed cogsets, you will see that the cable has the potential to wear a little groove in the adjacent metal as it works.

And while we are on derailleurs and shifter cables, have you ever noticed how the cable exits from the rear derailleur barrel stop at an angle that might just change as the cage shifts back and forth... and that on some derailleurs, there might just be metal-to-metal contact and an itty-bvitty groove wear its way into tha exit hole? Probably not.

And even though it's not metal, no-one has mentioned anything about the BB cable guide for both the rear and front derailleurs (front, bottom pull) that can contribute to this cable stretch thing, too.

I prestretched a wheel once, but it wobbled up and down too much.,,,,BD

Rowan: lol

You really have to be old school to remember that cable housing used to be unlined, and allowed metal to metal contact.

Oh, I began riding in 1974! I know the nasty feeling of that steel cable dragging through the unlined steel housing, especially on those fully housed rear brakes like my first Masi....

Someone is laughing his arse off at both of you.

I bow to your superior experience.

Cute.


But, as I do so, I should point out that I don't think all brake cable outers have a plastic lining.

Even the Wal*Mart trashmos have lined housing these days. There is no reason to not have it, short of nostalgia.


What about canti brakes... no metal to metal contact there? What about where the barrel or mushroom end goes... oh yes, I see that there on my bike, too. There's also a bike out there with ... wait for it... a travel agent with metal-to-metal contact between the cable and the pulley. That's without the straddle fitting for canti brakes where there is... wait for it, metal to metal contact!!

I think any discussion of cables and housing assumes that there will be some metal touching metal somewhere....:rolleyes:

But a cable sliding back and forth over other metal edges enough to wear a groove in them will probably result in the cable eventually fraying and failing. As someone who works on other people's bikes for a living, I do everything possible to prevent it.


Just occasionally, if you choose to work on bikes that may not be the current fashion trend, you might find cables running through a tube or two above the BB to the front and rear derailleurs... let me see on the (admittedly old frame up on the wall, a Maruishi)... yes! Metal to metal contact through one of those tubes!

Sure, but those are smooth tubes with plenty of surface area. The cables aren't wearing appreciable grooves into them, at least not large enough to affect cable tension, otherwise they'd be sawing through them eventually!


And, if you look at Sheldon Brown's little tweak for 9 speed shifters converting to 10-speed cogsets, you will see that the cable has the potential to wear a little groove in the adjacent metal as it works.

Link please. A search of sheldonbrown.com left me empty handed.


And while we are on derailleurs and shifter cables, have you ever noticed how the cable exits from the rear derailleur barrel stop at an angle that might just change as the cage shifts back and forth... and that on some derailleurs, there might just be metal-to-metal contact and an itty-bvitty groove wear its way into tha exit hole? Probably not.

The grooves you mentioned in your first post were apparently large enough to change the amount of slack present in the cable. That itty-bitty groove ain't gonna do it!


And even though it's not metal, no-one has mentioned anything about the BB cable guide for both the rear and front derailleurs (front, bottom pull) that can contribute to this cable stretch thing, too.

Not enough to measure, otherwise we'd be replacing them right and left.

Let me be plain. In a properly functioning, modern cable operated bicycle derailleur or brake set up, the minimization of sliding metal to metal contact by properly smoothing cable housing ends and ferrule openings is imperative to keep wear to a minimum and preserve smooth function. Top quality cables do not stretch after installation, but the housings can compress slightly, giving the illusion of a stretched cable.

Now leave me alone.....I have some chains to pre-stretch!:)

I believe that this is the most discussion I have ever had from one of my posts! Thanks for all of your responses!

Now, on to the pre-grimed bar tape they tried to sell me... :rolleyes: