# Changing my chainring, how much do I shorten the chain by?



## mmik (Oct 17, 2009)

I'm dropping from a 42T to a 32T, is there any magic range in how many chainlinks I should pop for the new size before I just start guessing?

If not, what's the best way to figure it out?


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## rlouder (Jun 26, 2007)

The general rule of thumb is thread it on the biggest ring and big cog without going through the derailleur and add 2 links.

I'm guessing you will be removing ~10 links (42-32) but check it first.


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## b-kul (Sep 20, 2009)

^yep. i do big big plus a few, just so if i accidently cross chain i wont blow anything up.


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## AndrwSwitch (Nov 8, 2007)

5 links/10 rivets depending on how you count. Or just size it as described above. If you're not changing rear derailleur, you can also leave it alone. Because I'm lazy, and wouldn't want to create extra messing around for myself if I decided 32t is too low, I would probably not shorten my chain at all if I was just replacing my big ring with a bash and not changing anything else, at least until putting some miles on the new setup.


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## mmik (Oct 17, 2009)

Actually, no derailleur, so it must be as simple as removing about 10 links.


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## AndrwSwitch (Nov 8, 2007)

No derailleur makes it a little more complicated, at least in terms of the math.

Luckily, you have a bike you can use as a measuring stick. You probably won't get a lot of choices about chain length once you've got your new chain ring mounted. What do you use to adjust tension?


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## mimi1885 (Aug 12, 2006)

Are you putting any guide on? I did with mine when I went 2x9, I resized the chain but ended up adding a few links to slacken the chain.


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## mmik (Oct 17, 2009)

My bike has horizontal dropouts and those back-facing bolts that I assume are to fine-tune the rear tire forward and back? I don't exactly know how it works, but I assume someone knows what I'm referring to.


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## AndrwSwitch (Nov 8, 2007)

The back-facing bolts are called "chain tugs." I don't know how they work either, honestly - my singlespeed used front-facing horizontal dropouts, and I found I didn't need any hub retention beyond the quick release. This was a commuter I rode in a fairly high ratio, so if someone says that a chain tug is necessary on a singlespeed MTB, I'll believe him.


BMX freewheel threaded on an old-fashioned road hub by Andrew183, on Flickr

OP, you might have mentioned it's a singlespeed in the first place.  Those first several completely off-the-wall answers would probably not have been posted, but they make plenty of sense on a geared bike.

Anyway, how you size your chain, exactly, is going to depend a little on how permanent you see this drivetrain configuration being and how long your dropouts are. A lot of singlespeeders have a couple of different cogs they choose depending on conditions, and there are some funky drivetrain layouts out there too. In general, though, you need a chain length that lands your axle somewhere in the dropout. Then, you'll position your axle in the dropout so there's a little bit of tension on the chain but everything turns freely. Too much tension will make a spot with extra resistance, and too little will allow your chain to fall off. Singlespeed drivetrains can be surprisingly fiddly.

If you have multiple cogs you use, try sizing your chain to be just long enough for the new chainring and largest cog. Hopefully your dropouts are long enough to let you use your smallest cog without shortening the chain.

Pics, or it didn't happen.


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## mmik (Oct 17, 2009)

Well my choices are between 32T and 42T, so I think I'd need a second chain. XD


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## dciandrew (Mar 1, 2011)

*Hijacking this thread if you don't mind.*

I'm changing out my rear cassete from a 11-28 to a 12-36 and am changing from a short cage to a long cage and was wondering how much chain I might need to add.

Crank is a 34 x 50. FWIW this is my road bike but I'm doing a ride with 13,500' of climbing this summer and need the help.

Thanks,


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## AndrwSwitch (Nov 8, 2007)

Awesome threadjack. You're not asking about a singlespeed or a mountain bike.

Just get a new chain, and start over on sizing. Chains wear as a unit, so adding links is a no-no. Chains are also cheaper than cassettes, so when replacing a cassette, unless it was putting on the new chain that revealed its wear, it often makes sense to get a new chain, to get the most service life from the cassette.


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## mmik (Oct 17, 2009)

i dont mind the jack, i'm not that way.but does anyone know anything about adjusting my tension with what i have?


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## dciandrew (Mar 1, 2011)

AndrwSwitch said:


> Awesome threadjack. You're not asking about a singlespeed or a mountain bike.
> 
> Just get a new chain, and start over on sizing. Chains wear as a unit, so adding links is a no-no. Chains are also cheaper than cassettes, so when replacing a cassette, unless it was putting on the new chain that revealed its wear, it often makes sense to get a new chain, to get the most service life from the cassette.


I know I needed the new chain, but I've never had to measue before becuase I always had the old chain as a reference. Was just looking for an approximate link count to get me close to where I should be. FWIW the chain on the bike is still in good shape so I'm going to keep it for going back and forth between the cassets and I don't need a 12-36 in my normal weekend rides, but the Climb to Kaiser is a killer of a ride for those in great shape let alone someone who seems never able to drop that last 20lbs.


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## mmik (Oct 17, 2009)

Haha, well I'm sure my chain will be good at 10 links less like a couple said, but I don't know what to do about my tire. :\


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## AndrwSwitch (Nov 8, 2007)

dciandrew said:


> I know I needed the new chain, but I've never had to measue before becuase I always had the old chain as a reference. Was just looking for an approximate link count to get me close to where I should be. FWIW the chain on the bike is still in good shape so I'm going to keep it for going back and forth between the cassets and I don't need a 12-36 in my normal weekend rides, but the Climb to Kaiser is a killer of a ride for those in great shape let alone someone who seems never able to drop that last 20lbs.


To make that drivetrain work, you're going to need a pretty big rear derailleur. So start by looking up your derailleur capacity - should be on the Shimano or SRAM web site, depending on what brand it is. That refers to the difference between the fewest teeth and most teeth your drivetrain combinations can give you. So for a 50/34 crank and 12-36 cassette, the most-teeth combination is 86 and the fewest teeth combination is 46. You need a rear derailleur with a 40t (!) capacity. That's a lot - more than a typical road derailleur. So you may want to back down a little in the gear range you choose, or if you have a 9-speed road bike, you can put a 9-speed MTB derailleur of the appropriate brand on the back of your bike and you're good. Another problem is that depending on the construction of the cassette you buy and your freehub, cogs that big have been reported to chew up people's freehubs pretty badly.

The compatibility issues involved in making road and MTB stuff work together on a 10-speed setup are more complicated. I think a 9-speed MTB derailleur would work and a 10-speed wouldn't, but I'm happy enough with the existing rear derailleurs on my road bikes and haven't researched the issue. When I installed a cassette that maxed out the capacity of my rear derailleur, I found getting the chain length right to be a little finicky, so I don't recommend going over the spec.

If you have the right rear derailleur, sizing is just big-big +1 link. (A link, here, is both the outer plates and the inner plates. If you're using a SRAM chain, the power link counts as a pair of outer plates.) Shimano has a different method they recommend, but it often results in a slightly longer chain and if you're pushing it on the gear range that the derailleur can handle, I think it's better to go a little shorter.

I'd suggest that changing your drivetrain back and forth is more trouble than it's worth, especially with Shimano chains, or 10-speed SRAM. If the jumps on a 12-36 cassette are big enough to bother you, a triple crank and narrower cassette might be a better way to go. That will also be more forgiving of chain sizing issues - on a triple, if the small/small combination causes the chain to drag on the derailleur cage a little, it's no big deal. IMO, on a double, you should really get it right.

I'm doing the weight thing myself this season. 9 more pounds, and I'm at my goal weight. I actually race better a little lower than that, but it doesn't give me any sort of a margin before I start having health issues. Frustrating that we can't magically be at our peak performance weights without having to work on it.


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## dciandrew (Mar 1, 2011)

I'm going to use an long cage X9 in the back. Its rated for a 36 casset and all my drivetrain is Sram so that part shouldnt be a problem. They only time I'll use the 12-36 is for this event and its training. So switching once a year is not big deal.

So with that being said are you saying I would need 87 links?


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## AndrwSwitch (Nov 8, 2007)

I don't know how long your chainstay is, so I really have no idea how many links you'll need. I'd guess closer to 114.

If you insist on figuring out the number rather than just sizing it to the bike, Park Tool is happy to help you.

https://www.parktool.com/blog/repair-help/chain-length-sizing

The mathematical methods are near the bottom of the page.


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## mmik (Oct 17, 2009)

I seriously just ruined my chain for the second time. I don't know what I'm doing.


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## AndrwSwitch (Nov 8, 2007)

That sucks.

What did you do?

You'd have to really muck it up in order not to make something workable with some more tinkering and removable links. (Actually, what kind of chain is it?)


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## mmik (Oct 17, 2009)

I removed a few links, down to what looks like the correct length, but the center pin thing is missing from the link on both sides, so I can't rejoin them. If I remove another pin it's just going to do the same thing, and it'll be too short by then. (I don't mean the pin you push out, I mean the wide cylinder thing that's part of every other link.)


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## AndrwSwitch (Nov 8, 2007)

Do you have a digital camera? Or at least a camera phone? Learn to upload pictures, and I think this thread could be a lot more useful to you...

I think the wide cylinder thing you're referring to is the roller. Sheldon Brown has exhaustive articles about everything, including chains, so we can make sure we're talking about the same thing...

http://www.sheldonbrown.com/chains.html

Anyway, an inner link without a roller is not particularly useful anymore. An outer link didn't have a roller in the first place. You can't connect two outer links together. You can connect an outer and an inner with a pin, and you can connect two inners with a removable link, like a Power Link (SRAM) or a ConneX Link (Wippermann.)

What chain, exactly, are you using?


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## mmik (Oct 17, 2009)

whatever chain came with the bike, sorry, I don't know. It's a pretty standard chain though. I think it's the "bushingless" kind, like the right-side picture in that link. I think I can reattach the part I took off and use a masterlink to put the chain back together, but it's just a matter of figuring out how to take it apart properly now. (so I don't end up with two outer links again)


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## AndrwSwitch (Nov 8, 2007)

On many chains, you can't put them back together with a pin you've pushed out. Part of the pin gets sheared off on the way out, and you're asking for a failure during a ride by trying to reassemble that way. I've only ever broken a chain twice. That was one of the times.

So you're likely to need more master links to reattach anything. That's not terrible - theoretically one could make a chain entirely out of master links and inner links. But it's kind of annoying, since if you buy enough master links, you end up spending more than the cost of the chain in the first place.

"Pretty standard chain" is a meaningless expression. Multispeed bikes are likely to come with one of two brands, using completely different attachment styles, and singlespeeds can come with any of about three common sizes, with three different ways of assembling them that I know of. So that's why I asked which chain you have, exactly, or if you could take a picture of it. Do the outer links have writing on them?


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## mmik (Oct 17, 2009)

I believe you, but why are there so many tutorials online that show people breaking chains and reattaching them with the pin they pushed almost all the way out if it's such a bad idea?


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## AndrwSwitch (Nov 8, 2007)

On older chains, it was fine. The pins were enough wider than the outer link plates that if you reinstalled them correctly, they'd stick out on either side a little bit and everything would stay together. In order to fit on cassettes with more and more speeds, chains have gotten narrower and narrower, including the length of the pin - they don't stick out much at all on either side anymore. In order to make up for that, the ends are hit with something that makes them spread out a little bit at the factory. It's that material that gets sheared off.

That's why it's important that you figure out which chain you have, exactly. Shimano chains come with special pins that can be used to reattach the chain. It's also good to do it in a certain way that they detail in the manual. SRAM, Wippermann and KMC chains come with a link that can be fitted together by hand.

If someone told me they had a singlespeed chain that worked the old-fashioned way, I wouldn't contradict him. Singlespeed chains come in two widths, both wider than the 8-, 9- and 10-speed chains that I use on my bikes, and there's no reason they couldn't have the longer pins that the old style of chains had.

That's why it's important that you figure out which chain, exactly, you have. If you take a picture of your chain, someone on this forum may recognize it. It might also have a brand and model number stamped on the outer plates. Shimano and SRAM chains all say what they are on them. You can probably also download a manual (seems silly, but even chains have a manual) that gives the correct procedure for reconnecting the chain.

I'm guessing that this is a singlespeed conversion, from a multispeed mountain bike. But I'm not even really sure of that. So it would help if you said what you're doing, or photographed the whole drivetrain too. Otherwise, we could spend days going around in circles on useless information and factoids about drivetrains you don't have, rather than someone being able to tell you how to make your bike work so you can go back to riding it.


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## mmik (Oct 17, 2009)

Alright, I can explain. It's a bianchi DISS, SS by default, and the pins do stick out. the chain is sram, and the links are stamped "PC59"


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## mmik (Oct 17, 2009)

Also, here's a picture of my tensioner or whatever you wanna call it, if anyone can explain how to use it.


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## AndrwSwitch (Nov 8, 2007)

Service instructions.

http://www.sram.com/_media/techdocs/Chain_all_MTB_08_02.pdf

In this case, you can actually reclose the chain with an old pin. So that's good.

Looking at some pics of chain tugs, I think that the thumb screw pushes something against the back of the dropouts, moving the wheel back in the frame. I'd start with the thumb screw backed out as far as you can without the tire hitting the frame, size the chain just long enough to fit around the chainring and the biggest cog you own, or the one that's on there if you don't have spares, adjust the rear wheel until it's right and lock it down, and then tighten the chain tug so it's snug. It's just there as a backup, to prevent you from pulling the wheel forward in the dropout. You shouldn't need one on the non-drive side. A lot of singlespeeders with slotted dropouts size their chain long enough to slide the wheel forward and unmount the chain, but that's up to you. Although the other ways of getting it off the gears may not be ideal...

Throw out the links with missing rollers. Do you still have enough chain? If so, just add a link or a couple of links by pressing pins back in so that the chain is long enough. If not, time for a trip to your LBS.


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## mmik (Oct 17, 2009)

I'm gonna take it in to the LBS anyway because I can't get two of the chainring bolts tightened without a tool, so I'll see if they can salvage my chain for me.


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