6

I am learning to replace chain and freewheel (So far so good). After I put new freewheel and new chain on, the chain are too close to each other at the back now (as you can see in the photo).

enter image description here

I think I need to adjust rear derailleur, is it right? Or maybe the chain wasn't installed correctly ( I cycled around and think chain install seems not too bad).

  • 4
    Your chain is too long. – Daniel R Hicks Oct 26 '19 at 16:34
  • @DanielRHicks is right, unless your cage doesn't support your chain ring and sprocket size difference. But additionally you probably have it on the smallest chain ring and the smallest sprocket, i.e. the chain runs diagonally. That creates unnecessary wear on all components and is not recommended anyway -- simply avoid it and be done. Just shifting once should, by the looks of it, lead to an acceptable position. – Peter - Reinstate Monica Oct 28 '19 at 15:10
18

The chain is too long. Presumably you did not cut it down to size it when you installed it.

All chains are sold with excess length and must be sized to the bike. The length required depends on the length of the chainstays and size of the largest chainring and sprocket.

The easiest way to size the chain is making it the same length as the old chain. You can also find the required length by putting the chain on the bike on the largest chainring and sprocket (and not through the derailleur). This Park Tool video shows how it's done.


Update after getting info that the new chain was cut to length of old chain:

Don't just shorten the chain and see what happens, you need to follow the sizing procedure to make sure the length is right. If the chain is too short for the large chainring/largest sprocket bad things will happen if you attempt to change into that combination.

Before you do that, check that your derailleur has enough total capacity for the chainrings and sprockets you have. Your derailleur looks like a short cage version and may not be able to take up the chain slack necessary.

Total capacity needed is:

(difference in teeth between largest/smallest chainrings) + (difference in teeth between largest/smallest sprockets)

If you have a Shimano derailleur you can look up the specs here. Note there is a link to archive spec docs if you have an older model. If you don't know what model you have or can't figure it out post a pic of the derailleur in your question, and tell us road or MTB and how many cassette sprockets you have and someone will likely identify it for you.

  • Hi, I measured the new chain and old chain, it is actually the same length (maybe the old chain was too long as well). can I adjust the derailleur or the only way is to remove one link from the chain? – daxu Oct 26 '19 at 20:17
  • @daxu see update to answer – Argenti Apparatus Oct 26 '19 at 20:29
  • 1
    Note that if the old chain is the same length as the new chain it might still be too long. As in, the old chain has stretched to its current length. If the new chain is the same length it might cause it to slip on the hub. I always find it better to count the amount of links that were on the old chain and go for the same amount in the new chain. I think you'll notice then that the length will be different. – Bono Oct 28 '19 at 17:20
  • Yep, I always match link-for-link when sizing a new chain from an old one. – Daniel R Hicks Oct 28 '19 at 17:49
  • @Bono a 100 link chain (50") would have to stretch 2% to add 2 links (1 inner, 1 outer, 1"). A chain is normally considered trashed at 0.75%. – Argenti Apparatus Oct 28 '19 at 18:55
11

Argenti's answer is correct - your chain is too long.

Personally I don't bother calculating the numbers from the manufacturer's specs. I can generally assume that this combination of cassette/rear mech/chainring was built to work together, so its just a task of getting the chain the right length.

My method for sizing a chain when the old one is unavailable (or the wrong length)

  1. Wrap the chain around the big chainring and the biggest rear cog, and through the derailleur correctly. Have the free ends hanging downward.

  2. Use an old discarded spoke as a holder - bend a hook into each end and use it to hold the chain to length. Something like this:

Topeak super chain tool hook in use

  1. Pull slack from the chain until the rear mech's bottom jockey wheel is cocked forward agressively. Something like this (or perhaps even a little more)

enter image description here

  1. Then use your eyes to figure how much chain to remove, to join it and keep this angle.

  2. REMOVE THE WIRE HOOK! (guess how I know this.)

  3. And finally give it a test change. Your small-small combo should not end up as close as your initial photo.

Assuming you're not changing transmission components, most bikes will end up perfect this way. You need exactly enough chain to run in Big-Big without binding, and the rear mech will take up the slack from all smaller combinations.

Save and label the take-off links in case you need to do some bodgery later to repair damaged links.

  • 1
    The piece of wire to hold the chain together whilst working on it is so obvious it's genius. Beats the heck out of my method of trying to hold the chain together and work on it with my hands at the same time. :) – Scott Oct 28 '19 at 14:23
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Too long..by a lot..I've got a 11-40 9 speed on a long cage with a 34-50 upfront..and my chain is scary long ..but it's also just long enough(1chains not enough I need 3 more links..)..it was like this when I lengthend it first time ..took 1 link out and its fine has been since..

Try big big (chainring and cassete)..not in deraillier..and then to the nearest pin when pulled taught..and then plus 2 full links..never fails..I've fone this when a chain I swapped to a friends bike meant I had to resize my new chain..

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There is a formula some people use to calculate chain length. Measure the length between the center of the bottom bracket and the center of the axle in inches. Multiply by 2 and then add (the number of teeth on the largest chainring divided by 4 ) plus (the number of teeth on the largest freewheel cog divided by 4 ) plus 1. Round this total up to the nearest inch and that is the total length of your chain in inches. For a standard 1/2 x 3/32 inch chain There are 2 links per inch, so if you multiply the length by 2 it will give you the number of links you need.

0

From the photogoraph we can tell that although the derailleur is folded into an extreme situation, the chain around the jockey wheel is not yet making contact with the bottom straight run. It might rub a bit when the chain shakes up and down.

If the derailleur only folds into that extreme configuration when you shift onto the smallest cog (highest gear in the rear) together with the smallest ring in the front (lowest gear), it's not necessarily a problem. That's a nonsensical combination of gears that you wouldn't normally use, and if there is a tiny bit of a chain-on-chain rub in a nonsensical gear combination, it is of no consequence.

What you have to watch out for is that the chain is long enough when you simultaneously shift on the largest cog and ring. If it isn't, that can be disastrous when the shift attempt is made. Never shorten a chain without making sure it can fit that combination of gears.

-1

People are making this way too awkward and complicated. Just use your old chain as a guide to how long it needs to be and remove the excess links with a chain link remover and not cut the chain to length as some people have said. Then install the new chain....simple! I love how people over complicate this procedure.

  • 3
    OP already commented on how they did exactly that and the chain ended up too long. – JAD Oct 28 '19 at 8:48
  • You're right - these are not the first option which is exactly as your suggestion. But in this case the previous chain was also too long. Also, this method doesn't work if you've made a major change in your components, like a larger cassette or a different rear mech. – Criggie Oct 28 '19 at 18:55
  • If it's too long then make it shorter.. .IF you've changed set up then compensate...to reiterate, people are making this way harder then it is... – Matt Mogwai Oct 29 '19 at 9:10

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