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Old 08-20-02, 02:28 PM   #1
Skuda25
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New Chain Length

I just changed my Shimano Freewheel from a 12X23 to a 12X25 and I am about to install a new chain. I have read numerous manuals about how to check chain length.

But I wanted to make it easier -- Do anyone have an opinion on how many lengths should be added for a 25 versus 23????

1?
2?

Thanks,

Scott
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Old 08-20-02, 03:23 PM   #2
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Sheldon Brown says put the chain on the big ring,and big cog,without going thru the derailer.pull chain tight and add 1".I have yet to find a a reason to argue with that method.
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Old 08-20-02, 03:53 PM   #3
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I doubt that you will need to change the chain length for that little of increase. Put it on as is and try it first. If it works on the big & big you have a winner.
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Old 08-20-02, 04:17 PM   #4
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Small Small, and make sure the chain dosent rub on itself when going through the derailleur.
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Old 08-20-02, 06:41 PM   #5
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BOGUS! Does that guarantee that nothing gets ginked if one accidently gets into the big-big combo? Think about it.
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Old 08-20-02, 06:45 PM   #6
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1 link longer than the old one????
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Old 08-20-02, 06:52 PM   #7
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To me, the proper length is generally just enough to support SMOOTH shifting into and out of large-large. Ideally, you should add one half-link, because the half-circumference is increasing by 1 tooth. Since chains come only in even numbers of half-links, you should make no change if you had a little slack before; otherwise, you should add one inch, i.e., two half-links.
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Old 08-20-02, 09:09 PM   #8
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Quote:
Originally posted by pokey
BOGUS! Does that guarantee that nothing gets ginked if one accidently gets into the big-big combo? Think about it.
Bogus? Wow I dont think i've heard that in 1,000 years! And if your "accidentally" "getting" into big big......I have no idea what to say to that.....you need some help buddy.
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Old 08-20-02, 11:25 PM   #9
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KleinMp99 is right, "Eddy B" former US road team coach recommends this technique as well. It's easy, it works and keeps derailleur spring tension/wear to a minimum. I use several sizes of freewheels and cassettes on my bikes and have no problems leaving the chain-length(s) the same regardless the size of the "cluster".
The technique "pokey" recommends is probably OK too, he cites a source that seems to be popular. I've never tried it.

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Last edited by pat5319; 08-20-02 at 11:33 PM.
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Old 08-21-02, 02:03 AM   #10
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I swap 23T (for the flats) and 26T (for hill climbs) on 3 of my road bikes without adjusting the chain.

If the chain is set up correctly for 23T, a 26 should not require any change to the chain.
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Old 08-21-02, 06:09 AM   #11
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Likely as not, it's already long enough... do the Sheldon Brown test.

FWIW, here's what Shimano recommends:
http://www.shimano-europe.com/cyclin...87&ips_index=5
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Old 08-21-02, 08:20 AM   #12
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Thanks for all the advice. I went with the same length.

Thanks.
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Old 08-28-02, 01:55 AM   #13
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Sheldon Brown says put the chain on the big ring,and big cog,without going thru the derailer.pull chain tight and add 1".I have yet to find a a reason to argue with that method.
Please explain something to me. If the chain goes around only the ring and cog, and you pull it tight + 1 link, then how does that compensate for the additional length needed for the chain as it goes around the pulley wheels of the derailleur?

Would the chain not now be straight line tangential to ring and cog? Sorry if I missed something here.
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Old 08-28-02, 03:49 AM   #14
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Quote:
Originally posted by Bokkie

Please explain something to me. If the chain goes around only the ring and cog, and you pull it tight + 1 link, then how does that compensate for the additional length needed for the chain as it goes around the pulley wheels of the derailleur?

Would the chain not now be straight line tangential to ring and cog? Sorry if I missed something here.
I presume the theory is based around you never trying to get into BIG BIG while riding. Actually if you go with Sheldon Brown's method it shouldn't be possible to go BIG BIG coz the chain will be too tight to get there.

This is one of the reason's I dislike riding in the dark, I forget what damn gear I'm in. Its a relief to find a steep hill coz at least then I know in in gear combo 0

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Old 08-28-02, 10:02 AM   #15
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Some really serious weight weenies will run a chain a few links short of the Big-Big length. I wonder what breaks first, when they go for a too-large combination?

Last edited by roadbuzz; 08-28-02 at 10:07 AM.
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Old 08-28-02, 12:13 PM   #16
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Each link is 1 inch long, and contains two rollers.

You're adding 2 teeth, so, if the chain wrapped all the way around the sprocket, it would need to be 1 link longer.

Since it actually only runs half-way around, it only needs to be 1/2 link longer...assuming that it's already maxed out.

My advice is to try it with the existing chain and see if you can shift onto the large/large combination without any difficulty. If so, Bob's your uncle! If not, add a link. Half links aren't available for derailer chain, unfortunately.

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Old 08-29-02, 02:15 AM   #17
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Sheldon,

I've attached a crude image of the point that confuses me. In the diagram, A is the chainring, B the cogs. C are the derailleur pulleys. I've shown a line (crudely tangential) that shows the effect of pulling the chain tight around the big cogs excluding the derailleur pulleys? Add 1 link to this. That's how I've been reading the thread so far. If that is the case, how does 'tight' + 1 link provide sufficient length for the pulley wheels? Granted, it is not wise to run big-big no more than you want to run small-small, but have I completely lost the plot? I think I have but I can't see it in the current discussion. Please explain.:confused:
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Old 08-29-02, 06:01 AM   #18
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Umm......
You may not have noticed it yet, but that derailleur has a torsional spring. When you tighten the chain, those jockey wheels move forward, close to the direct line from the cogs to the rings.
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Old 08-29-02, 06:58 AM   #19
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Sheldon Brown says put the chain on the big ring,and big cog,without going thru the derailer.pull chain tight and add 1".I have yet to find a a reason to argue with that method.
I know what you are getting at, but did I take the quote above from the start of the thread too literally? The phrase I latched onto is "without going thru the derailer" and that implies not passing around the guide and torsion wheels? Trying to memorise it, but the additional length of the chain around the wheels is much longer than tight around big big + 1 link. If the consensus is like the way I drew it, then one extra link could not possibly account for the length required?:confused:

I'm obviously being too obtuse, but I'm trying to convert the words into something I visually latch onto. The reply that had the link (forgive the pun) to what Shimano recommend makes much more sense to me for it includes the guide and torsion wheels and I can see visually what they are saying. Maybe it's time for someone to show me visually what I'm failing to grasp using the power of the lexicon alone.
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Old 08-29-02, 07:16 AM   #20
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Here's what I do:

I take an old spoke, and cut it into about an 8" length. I bend both ends up (about 1") and in to create a chain holder (U shaped). I put both ends through a link on each end of the chain. This keeps both ends of the chain together, with some slack links, until I find the proper length.

I do the small-small combo and determine how many links I need to take off to keep the jockey pulley from rubbing the chain. I do not however, remove links yet, just determine how many, or put the chain together yet, it's still being held by my spoke thingy!

Then I carefully shift the chain into big-big, to check if it's long enough! This is done by backpedaling and maually moving the chain, because the chain isn't permanently attached yet!

If the length is good, I connect the chain. If too short I add a link(pair of links).

My theory is you shouldn't be in big-big OR small-small combo, BUT! If you accidentally shift into big-big it's better to have a chain too long that will allow you to be in big-big and rub in the small-small than too short for big-big and potentially rip your derailleur off!
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Old 08-29-02, 10:07 AM   #21
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I've attached a crude image of the point that confuses me. In the diagram, A is the chainring, B the cogs. C are the derailleur pulleys. I've shown a line (crudely tangential) that shows the effect of pulling the chain tight around the big cogs excluding the derailleur pulleys? Add 1 link to this. That's how I've been reading the thread so far. If that is the case, how does 'tight' + 1 link provide sufficient length for the pulley wheels? Granted, it is not wise to run big-big no more than you want to run small-small, but have I completely lost the plot? I think I have but I can't see it in the current discussion. Please explain.
That's what the "+1" is for. The pulleys and the parallelogram are spring loaded, and when in the big-big position, the pulleys are pulled forward quite a bit from where you show them.

Some old-fashioned rear derailers lack the spring-loaded parallelogram, so you might need to be a bit more circumspect with, say, your Hurét Alvit or Campagnolo Nuovo Record.

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Old 08-29-02, 08:00 PM   #22
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Hurét Alvit????

Ohmygawd! I actually still have one of those!!!
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Old 08-31-02, 03:05 PM   #23
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I changed my crankset from a 48/38/28 to a 42/32/22 .Should I shorten my chain?It seems to work great as is but will I run into problems?
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Old 08-31-02, 04:40 PM   #24
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Quote:
Originally posted by hillyman
I changed my crankset from a 48/38/28 to a 42/32/22 .Should I shorten my chain?It seems to work great as is but will I run into problems?
I always put a new chain on when replacing rings and or cogs. Why take the chance that wear from the used chain will wear the new rings prematurely, they cost too much for that!

Follow up by using the technique described by Sheldon Brown earlier in this thread to size your chain correctly.
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Old 08-31-02, 04:51 PM   #25
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Its a new bike.I put on a new 12-32 cassette also.I figured with smaller chainrings and a bigger cassette they would offset each other.Like I say, it seems OK.I just don't want to hit a BIG hole and end up with a chain necklace I'll try the Sheldon Brown thing when I have time.I'll put it off because it requires thinking.
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