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Just because a chain is "streched" does it need replacing?(8 posts)

Just because a chain is "streched" does it need replacing?Dutchy
Jan 14, 2002 7:52 PM
When I measured my Ultegra chain it was about 4mm/~1 sixth of an inch stretched.
It still shifts very smooth because I have kept it well maintained. It is the original chain that came
with the bike. Should I replace it because it has stretched or should I wait until it starts to
shift roughly? People recommend to change a chain and cassette at the same time, if this is
true why don't the chainrings and rear-der cogs gets changed at the same time also?

The way I see it. At the moment all the cogs are "bedded in" a new chain and cassette will have
to work with a worn chainring and rear-der cogs, this can't be good, can it?

Chain replacement is a good ideaspookyload
Jan 14, 2002 8:52 PM
If you let a chain go for too long, it will stretch alot, and in turn, the stretched chain will score the cogs at it's longer length. When this happens and you put a new chain on, it will sound like it is skipping, and you will have to replace the cogs. So the key is to detect the stretch early, and replace the $20 chain, as to save having to replace the $60 cogs as often. If you change chains on a regular basis, a cogset could last for years. Parks chain checking tool is a very easy tool to use, and it is very cheap. Just give it a check every other week or so, and things will go smoothe.
I'd change itpmf1
Jan 15, 2002 4:56 AM
When a chain has stretched, its time to change it. Once it gets to this stage, it will damage your cassette. If you change chains frequently, there is no need to change your cassette everytime you change your chain. I've had LBS tell me that one should change a chain every 1000 miles. This seems way to frequent to me. I typically go 3000 miles between changes. Chains are pretty cheap and easy to change. You'll know if you need to change your cassette if shiftinf is not good after you change the chain.
re: Just because a chain is "streched" does it need replacing?grzy
Jan 15, 2002 9:08 AM
Lots of things don't fail sudeenly and catastrauphically. Over time they just get a little worse and may have an effect on other things. You can probably go a little further but you run the risk of going too far. Also recognize that the failure mode isn't linear - once things start to go it happens very fast. This is really aparent on a MTB, but holds true on a road bike. Chains are pretty cheap compared to cogsets and chainrings and a broken chain in the middle of nowhere. The danger of replacing a chain too soon is that maybe you buy 5 chains in two years (or whatever your time frame is) vs. just four chains. The alternative is that you buy just 3 or 4 chains then get to pop for a new cogset and chainrings. The lowly chain has one of the toughest jobs on the bike (along with tires) - it's whole life is about lots of metal on metal contact with grit and sometimes inconsistent to poor lubrication. Ultimately it is desinged to fail. There's a reason why chains are avoided when possible on mechaincal things. However, they are a pretty efficient means of transmitting power which is why you see belts on Harley Davidson motorcycles, but still chains on everything else. Chains actually introduce a variatiuon in speed at the driven gear due to the geometry issue of a bunch of little straight line segments vs. a smooth and continuous belt. Typical Harleys aren't racing bikes and they all ready have the vibration issue covered.

You chain is wearing out - and like the Fram filter ad - you can pay now or pay later. What are you saving?

BTW - my wife would ride her bike huge distances and then come to me with a shifting problem (before we were married) - I'd be struck dumb when I realized that the whole drivetrain needed to be replaced. Her chainrings and cogs were so hooked they looked like blades off a table saw. Old French components are hard to find these days and expensive. Her bike still worked, but not very well.
Replace chain to avoid replacing casette... as for chain rings..PdxMark
Jan 15, 2002 10:26 AM
if the chain wear goes "too far" it will also wear the casette to the point it needs to be replaced. Early chain replacement gives you more life out of your casette.

Chain rings wear MUCH slower than the casette. Others will know better, but basically the small diameter of the casette cogs result in a couple wear-inducing factors. First, relatively few casette teeth bear the load at any one time in comparison to a larger number of chaing ring teeth. The result is that the load on each casette tooth is proportional greater. On top of that, the smaller diameter means that the extra load is applied to each casette tooth more often than to each chain ring tooth. This wouldn't be an issue if we all rode 1-to-1 granny gear bikes.
Yes, it doesRusty McNasty
Jan 15, 2002 2:20 PM
By now, with 1/6" stretch, the pins inside each link are just about gone. Any day now, that chain is going to snap.
Of course, your cogs are toast now, too. They cr@pped out when your chain was about 1/8" stretch, and when you finally DO replace the chain, the teeth will be so worn that the chain will skip right out of the cogs. I've seen this happen DOZENS of times.
You cheaped out, now you've ruined the cogs, too! Doesn't make any sense to save $20, when it's going to cost you $60 in the end, does it?
It's already goneKerry Irons
Jan 15, 2002 5:26 PM
You've already gone past any reasonable replacement point, and most certainly at least a couple of your cassette cogs are worn out too. A modern chain in an 8+ cog setup should be replaced at 1/16" elongation in 12", 1/8" at the most. By letting the chain go so far, you may have damaged your chain rings too. The reason the chainrings don't normally need replacing is that the chain is engaging so many more teeth up front compared to the cassette. A visual inspection of your cogs will almost surely show you a bunch of "shark fin" teeth, and if you mounted a new chain only, the chain will most likely skip over those worn teeth. This can be a nasty surprise if you're climbing out of the saddle. My own recipe is to buy good ($20-25) chains that last a long time (10K miles or so) before they reach the 1/16" elongation point, and then replace the cogs at the same time. In my setup, that's $75 every 10-12K miles. Others claim they can save the cogs by replacing the chain much more frequently, but you can do the math - they spend $75 on chains and still have worn cogs at 10-12K miles. To each his own. YMMV.
Thanks everyone!Dutchy
Jan 15, 2002 9:28 PM
Yes you were all right, on very close inspection I noticed some "burring" of the metal on the most used cogs.
I stripped them apart in September, and they looked OK. Obviously when they wear out they go fast and
just get worse. So now I'm in the market for a new chain and cassette.

Thanks everyone. Lesson learned!