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How to measure correct chain length?
#1
Hi guys

I just watched Alex's video below on how to measure correct chain length.
http://bikeride.com/calculate-chain-length/

Can anyone tell me if the same procedure applies to a single speed crank? Because I have tried the exact procedure Alex demonstrates in the video and my chain seems terribly short and the derailleur is getting way too overstretched especially when I change to the lower gears.

By the way, I have a single speed crank and a 7 speed freewheel.

Thanks in advance for any suggestions.
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#2
Shimano and SRAM's recommendation is to wrap the chain around the largest ring and largest cog, round up the length to the next full link then add one inch - which is exactly the same as Alex suggests.

I have always followed this procedure and never had any issues - over almost a dozen different bikes, some single, some double and some triple chainring.
Nigel
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#3
(05-28-2013, 12:05 PM)nfmisso Wrote:  Shimano and SRAM's recommendation is to wrap the chain around the largest ring and largest cog, round up the length to the next full link then add one inch - which is exactly the same as Alex suggests.

I have always followed this procedure and never had any issues - over almost a dozen different bikes, some single, some double and some triple chainring.

Hi Nigel

Thanks for your reply. I take it when you wrap the chain around the biggest chainring n cog to work out the chain length, you bypass the rear derailleur just as Alex suggests? I have a Sram derailleur by the way if that matters.

Thanks
  Reply
#4
(05-28-2013, 02:19 PM)ibie1983 Wrote:  Hi Nigel

Thanks for your reply. I take it when you wrap the chain around the biggest chainring n cog to work out the chain length, you bypass the rear derailleur just as Alex suggests? I have a Sram derailleur by the way if that matters.

Thanks

Yes. It is also pictured that way in the Shimano and SRAM instructions.

Shimano instructions can be found on line, search for: Shimano Tech Docs. I do not know if SRAM has an easy online source.

My last RD install was the X.9 on our T50 - works great with a SRAM 11-34T 9 speed cassette, and 26-44-54 triple on the front. It even shifts smoothly into and out of the 34-54 combination which is not recommended. That was less than two months ago.
Nigel
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#5
Hi Nigel

I have done exactly as you n Alex have recommended but i am not getting the same result. My chain is now way too short n my derailleur is way overstretched. I will post picture in a couple of days as im now having problem with my chain tool. Cheap n nasty tool. I have bought a new n quality one so will post picture when i can.

Many thanks
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#6
Thread the chain through the derailluer and on the chainring and largest cog, pull till cage is vertical 90 degrees from horizontal, subtract one link ( inner and outer = 1 link ) . Connect
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#7
Hi Nigel

Please find attached picture of how my chain/derailleur gets overstretched once I install the chain through the derailleur and shift to the largest sprocket or gear 1. I have followed both Alex and your recommendations and calculated my chain length by putting my chain over the chainring and biggest sprocket and bypassing the rear derailleur. Kindly advise why it is going so wrong.

Ibs
Hi Painkiller

I will try your suggestion. Not sure im understanding you right though.

Thanks
  Reply
#8
(05-28-2013, 10:31 PM)painkiller Wrote:  Thread the chain through the derailluer and on the chainring and largest cog, pull till cage is vertical 90 degrees from horizontal, subtract one link ( inner and outer = 1 link ) . Connect

Hi Painkiller

Do you mean pull the cage till it is vertical and almost parallel with the axle, and then remove one link? I've done that and I now have my chain as pictured in biggest sprocket or gear 1. Can you tell me from the picture whether I have the correct chain length?

Many thanks
  Reply
#9
looks much better, now lets see a pick with the chain on the smallest cog.
as long as the chain does not touch the pulleys you are good to go
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
  Reply
#10
PK's suggestion looks like the way to go, especially with only a single chain ring up front. With a double or triple, it may not work so well in the smallest cog.

Even the upper picture is okay if the RD has some additional motion left.
Nigel
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#11
On a single front chainring set up, I'd do the opposite measurement. Put the chain on the smallest rear cog and pull it tight until the pulleys just stop rubbing. That's the longest chain your setup allows. With that chain length, if the rear der pulls too tight on the big cog, you need a longer cage derailleur.
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#12
@ painkiller i will post pic of chain on smallest sprocket when i get home on Monday.

@ Dave thanks for the suggestion. I will give that a try.

As you're all giving different suggestions, does that mean theres no right way of doing it n theres no exact chain length? But rather, as long as it looks ok, then thats fine?

Is it possible to get Alex's suggestion himself on this or he does not come on these forums?

Many thanks
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#13
Do not get the wrong impression, I was merely offering a suggestion that would stop your over stretching of the chain. For some reason the tech docs failed you. I do not know why, they work for me.. I have not seen Alex's video to compare. Daves suggestion may be fine, however still leaving a chance for over stretching. lets see the pic. and go or stop from there. I am confident it will be fine. At least to the point if any other adjustments are needed you would be removing and not adding a link.
There is more than one way to skin a cat as they say. I wish we could tell you what you were not grabbing about the tech docs as they are correct.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#14
(06-02-2013, 12:19 AM)ibie1983 Wrote:  As you're all giving different suggestions, does that mean theres no right way of doing it n theres no exact chain length? But rather, as long as it looks ok, then thats fine?

There is no single "right" way to measure a chain and there's no exact amount where your rear der is too stretched. But in the first picture, it looks too far to me.

The standard way of measuring the chain (big to big chainrings) has to allow for also dealing with small to small without the chain rubbing on the der. Since you don't have a small front chainring, you can use a longer chain that this measurement system would indicate.

All other things being equal, a longer chain is preferable because you spread the wear out on more links and it will last longer. But that's a minor consideration.
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#15
This looks great if it doesn't have sag issues in high gear. You might want to trim that derailleur cable before you impale something important.
[Image: attachment.php?thumbnail=4202]
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#16
(05-31-2013, 09:46 PM)painkiller Wrote:  looks much better, now lets see a pick with the chain on the smallest cog.
as long as the chain does not touch the pulleys you are good to go

Hi painkiller

Here's the pic with the chain on the smallest cog. Does it look like the chain is a tiny bit too long or do you think it is ok?

Thanks
  Reply
#17
looks ok; a couple links either way will work on most bikes, except crazy ones like our T50 with a 11-34 cassette and 26-44-54 triple on the front.
Nigel
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#18
as long as the derailluer has some tension and is not touching itself and rides fine your good to go. The pics are a bit grainy making it hard to judge depth, maybe a shot from the rear may help the view.
Hopefully the saga is over. Let us know how it works
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
  Reply
#19
(06-03-2013, 09:53 PM)painkiller Wrote:  as long as the derailluer has some tension and is not touching itself and rides fine your good to go. The pics are a bit grainy making it hard to judge depth, maybe a shot from the rear may help the view.
Hopefully the saga is over. Let us know how it works

Ok I will upload another picture later. The problem is I cant upload a high resolution picture as the site wont accept attachments more than 2mb in size so ive had to set my phone to a lower resolution setting and take the picture.
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#20
I see. I use a camera and size by pixels in photoshop then post. they normally run about 800k. I do not have a cell phone so I could not offer suggestions on that.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
  Reply


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