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Old 05-29-09, 01:21 AM   #1
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Chainring 42T to 52T, new chain

I am changing a 42T chainring to a 52T chainring (largest ring), will I need a longer chain?
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Old 05-29-09, 08:56 AM   #2
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I see several people have viewed this and left it alone. Well, somebody has to do it.

It's hard to answer this without sounding insulting, so please don't be offended but if you have to ask this question, you really shouldn't be doing your own work.

Get your bike to a bike mechanic and you will undoubtedly be glad you did.
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Old 05-29-09, 09:25 AM   #3
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I would somewhat agree, but we all have to start learning somewhere.

But the answer to the original question is yes. Learning how to size a chain can be learned from various sites like parktool.com or sheldonbrown.com among others. They also explain the proper methods and tools for doing the work. Or a bike shop will do the replacement for only a few dollars if you buy the chain from them.

You could theoretically add links to the existing chain, but unless you have spare links laying around, the easy answer is to replace the chain. Especially if the chain is not fairly new, this is probably the best answer.
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Old 05-29-09, 09:34 AM   #4
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Good chance that the derailleur will need some repositioning and adjustment, also.
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Old 05-29-09, 09:48 AM   #5
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Good chance that the derailleur will need some repositioning and adjustment, also.
Actually, I just thought of the fact that the front derailleur may need to be replaced. a derailleur installed on a bike with a 42 tooth ring may not be rated to work with a 52 tooth ring.

The jump down to the smaller ring may be a bit much too, so replacing the smaller rings may be in order to maintain reasonable shifting.

Definitely the gap between the largest and smallest ring must be within the range of the derailleur.
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Old 05-29-09, 11:52 AM   #6
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I see several people have viewed this and left it alone. Well, somebody has to do it.

It's hard to answer this without sounding insulting, so please don't be offended but if you have to ask this question, you really shouldn't be doing your own work.

Get your bike to a bike mechanic and you will undoubtedly be glad you did.
The fact that I thought things through and predicted snags before changing anything shows that I have the capability to work on my own bike. The question could have easily been answered without sounding insulting. This is bike repair, not molecular biology, physics or biochemistry.

Thanks to the other posters for posting thoughtful replies.
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Old 05-29-09, 12:14 PM   #7
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When you get a new chain you will need to decide if you want to go stainless steel rust proof. Or other choices.
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Old 05-29-09, 12:45 PM   #8
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You will need a new chain- but more important will be setting the height of the front derailler. This could take a bit of time to get right so the Park Tool or Sheldons Web pages may help you on this.

Another problem is why are you going to 52? What are the other ring sizes on the bike? The front derailler can only handle a jump of so many teeth- although that can be stretched a bit if you know how to set up the derailler properly.
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Old 05-29-09, 03:33 PM   #9
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The fact that I thought things through and predicted snags before changing anything shows that I have the capability to work on my own bike. The question could have easily been answered without sounding insulting. This is bike repair, not molecular biology, physics or biochemistry.

Thanks to the other posters for posting thoughtful replies.
Ok, a couple things here:
  • You will almost certainly need a new chain. The chain-sizing method that I use is to wrap the chain around the big-big combination (don't go through the derailleurs) and add two links.
  • It's possible that your old chain has worn your current cassette to the point that a new chain won't work with your current cassette. Measure your current chain; if the 0" mark on your ruler lines up with a chain rivet, then the 12" mark should too. A little variation is ok; if it's more then 1/8", you almost certainly will need a new chain.
  • The "curve" of your front derailleur needs to roughly match the "curve" of your largest chainring, although if you adjust carefully, your current front derailleur can probably work with your new setup.
  • What is your current chainring setup? i.e., is this a single chainring, double, triple setup? The "tooth jump" of a normal compact (i.e., 34 to 50 teeth, so a 16-tooth jump) leads to frequently dropped chains unless you're careful with the setup. If you're going to wind up with a larger gap then that, you'll probably want to install a chain catcher.
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Old 05-29-09, 06:43 PM   #10
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I'm a fairly longterm bike owner, and this is one of the things I'd have my LBS do.
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Old 05-30-09, 06:18 AM   #11
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The fact that I thought things through and predicted snags before changing anything shows that I have the capability to work on my own bike. The question could have easily been answered without sounding insulting. This is bike repair, not molecular biology, physics or biochemistry
Look, all I'm saying is it takes a certain amount of aptitude to successfully perform mechanical tasks.

I'm blessed or cursed with a 98 percentile in Spatial Relationships. This allows me to perform mechanical, engineering and fabricating tasks quite well. The curse part is that my friends are constantly giving me their broken things to fix.

However, where mathematics are concerned, I'm at the bottom of the heap. I can't do the simplest calculations in my head, nor can I figure out the equations most of the time. It would be foolish for me to do my own accounting and taxes. That's why I hire a professional to do it.

If you can't look at a situation of increasing the circumference of something and instantly know it will require more length in the thing you are wrapping it with, you should consider that you might not be cut out to work with it. You also posted the question the GCD section when it clearly is a mechanical question.

I'm absolutely certain that there are things you are good at, but judging by the fact that you weren't sure about a very basic mechanical/geometrical problem, if you try to do your own wrenching, you stand a good chance of ruining components or creating an unsafe situation for yourself and/or others.

No it's not molecular biology, physics or biochemistry but there are critical measurements and adjustments involved when you make changes to your bike. You not only need the knowledge but the aptitude and skill to successfully carry out some changes.

This probably just sounds even more insulting and I apologize if it does. Being somewhat of a geek, my interpersonal skills are sometimes lacking.
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Old 05-30-09, 08:57 PM   #12
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Look, all I'm saying is it takes a certain amount of aptitude to successfully perform mechanical tasks.

I'm blessed or cursed with a 98 percentile in Spatial Relationships. This allows me to perform mechanical, engineering and fabricating tasks quite well. The curse part is that my friends are constantly giving me their broken things to fix.

However, where mathematics are concerned, I'm at the bottom of the heap. I can't do the simplest calculations in my head, nor can I figure out the equations most of the time. It would be foolish for me to do my own accounting and taxes. That's why I hire a professional to do it.

If you can't look at a situation of increasing the circumference of something and instantly know it will require more length in the thing you are wrapping it with, you should consider that you might not be cut out to work with it. You also posted the question the GCD section when it clearly is a mechanical question.

I'm absolutely certain that there are things you are good at, but judging by the fact that you weren't sure about a very basic mechanical/geometrical problem, if you try to do your own wrenching, you stand a good chance of ruining components or creating an unsafe situation for yourself and/or others.

No it's not molecular biology, physics or biochemistry but there are critical measurements and adjustments involved when you make changes to your bike. You not only need the knowledge but the aptitude and skill to successfully carry out some changes.

This probably just sounds even more insulting and I apologize if it does. Being somewhat of a geek, my interpersonal skills are sometimes lacking.
You ought to rethink your own bicycle knowledge before you pass judgement on another person's bicycle repair aptitude.

Increasing the chainring diameter does not necessitate increasing the chain length. The whole point of getting a bigger chainring is to be able to travel faster at a given pedalling rate. It would be counterintuitive to gear into the largest chainring in combination with the largest rear cogwheel. In this instance, a larger chain would be required, but this is not how normal cyclists ride. There IS slack in the chain where the rear derailleur picks up. The slack MAY or MAY NOT give enough clearance for an increase in the chainring diameter. This would obviously be in the case where the smallest rear cogwheel would be used with the largest chainring to increase top travelling speed for a given rate of pedalling. That is why it is not 1:1 chain length increase and chainring increase.
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Old 05-30-09, 09:25 PM   #13
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Increasing the chainring diameter does not necessitate increasing the chain length. The whole point of getting a bigger chainring is to be able to travel faster at a given pedalling rate. It would be counterintuitive to gear into the largest chainring in combination with the largest rear cogwheel. In this instance, a larger chain would be required, but this is not how normal cyclists ride.
It may be 'counterintuitive' to shift into the large/large combination, but I think it's dangerous to set up the chain length so it's too short to accommodate such a shift. Even if you know to avoid it, it is not unlikely that someday when you're tired and faced with a sudden grade increase you might reach for the rear shift lever and shift to the big cog while forgetting that you're still on the large ring in front. If the chain is too short that can quickly result in a lockup of the drivetrain, a bent derailleur and/or hanger, and possibly a crash. Better to have a long enough chain. And yes, the RD can take up a certain amount of slack, but an increase of 10 teeth is a lot and I'd expect a longer chain to be needed unless his current setup already has a much longer chain than was needed or optimal.

Another consideration for the OP is whether the chain wrap capacity of his current rear derailleur can handle the range of his new chainrings and whatever cogs he has in the rear. A more complete specification of his drivetrain would be useful to those offering advice - i.e. what other chainrings are on the front, what derailleur models (and whether short vs. long cage), and what range of cogs on the cassette/freewheel.
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Old 05-31-09, 12:09 AM   #14
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It may be 'counterintuitive' to shift into the large/large combination, but I think it's dangerous to set up the chain length so it's too short to accommodate such a shift. Even if you know to avoid it, it is not unlikely that someday when you're tired and faced with a sudden grade increase you might reach for the rear shift lever and shift to the big cog while forgetting that you're still on the large ring in front. If the chain is too short that can quickly result in a lockup of the drivetrain, a bent derailleur and/or hanger, and possibly a crash. Better to have a long enough chain. And yes, the RD can take up a certain amount of slack, but an increase of 10 teeth is a lot and I'd expect a longer chain to be needed unless his current setup already has a much longer chain than was needed or optimal.

Another consideration for the OP is whether the chain wrap capacity of his current rear derailleur can handle the range of his new chainrings and whatever cogs he has in the rear. A more complete specification of his drivetrain would be useful to those offering advice - i.e. what other chainrings are on the front, what derailleur models (and whether short vs. long cage), and what range of cogs on the cassette/freewheel.
I realize this. Especially for this reason as I found out through more digging that it would compromise safety. And from further thought experiments considering the "slack" in the chain would not be enough to accommodate the 52T. Even if it did, there may be a lock up. I had considered making it a pseudo fixed gear, shifting down once maximum, and using the highest gear at 98% of the times. But "off" days may happen.

So long, and short of it, yes, it would be okay to keep the chain, but, it would not be the best idea, and more than "okay" it would be better to go with a slightly longer chain.
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Old 05-31-09, 06:50 AM   #15
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Gee, I'd have thought that if you already had all the answers, it would not have been necessary to ask the question.

All of the replies offfered good, in depth, information, when taken as a whole.

Lighten up!
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Old 05-31-09, 08:16 AM   #16
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Quote:
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Increasing the chainring diameter does not necessitate increasing the chain length.
Increasing the the size of the big ring by 10 teeth = Need to lengthen the chain

(Except in rare circumstances)
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Old 05-31-09, 10:01 AM   #17
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gee, i'd have thought that if you already had all the answers, it would not have been necessary to ask the question.

All of the replies offfered good, in depth, information, when taken as a whole.

Lighten up!
No! You Lighten Up!!!
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Old 05-31-09, 01:23 PM   #18
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Tsk, tsk, tsk....
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Old 05-31-09, 11:31 PM   #19
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Tsk, tsk, tsk....
And Now For Something Completely Different:

OP: Yes, you will need a longer chain if you increasing the size of the chainring.
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