# Snapped Chain requires new cassette?



## JuliaT (22 Jul 2019)

Hi all,

During my commute this morning my chain snapped. I took the bike to the shop as I had no tools or knowledge on how to replace it (specially in the middle of the street and having a meeting in the morning).
The guy in the bike shop told me that, as I through away the snapped chain he would have to change the cassette. That they have to be replaced together... if not I will have problems with the new chain...

I am a beginner so I have no idea... My question is... is this for real or is he trying to scam me? If I have to change the cassette I will do it, no problem, but this sounds weird to me...

Thanks!


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## ianrauk (22 Jul 2019)

It's all dependent on what mileage the chain and cassette have done and what condition they are in.
If it's a relatively new cassette and chain with little mileage then a new chain might work with the old cassette. If they have done a good few miles then a new chain may not mesh with the old cassette causing the chain to skip and jump.


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## bigjim (22 Jul 2019)

Depends how worn the old chain is. The chain has usually had to be pretty badly worn to require a cassette change. Also a chain snapping is not a sign of a worn chain. It's quite a rare occurrence. Were the gears skipping before the chain broke? I'd be tempted to fit just the new chain. You will soon know if the cassette needs changing as the gears will start skipping about. So. he's wrong. They don't always have to be changed together at all. Change chains early enough and cassettes will outlast quite a few chains.


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## johnblack (22 Jul 2019)

You don't have to, but if your chain and cassette are the same age and the chain is worn, changing the cassette isn't a bad idea, it shouldn't cost a great deal, depending on what groupset your using obv.


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## Ian H (22 Jul 2019)

Cassettes wear as the chains wear, and fitting a new chain to an old cassette will often result in the chain slipping on some sprockets. Did he ask you how far you'd ridden on the current chain/cassette, or measure the wear on the snapped chain?


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## MichaelW2 (22 Jul 2019)

If you change your chain before it becomes to worn, you can use the old cassette. Further wear will result in sharks teeth profile wear in the cassette. The old chain will work but a new chain will slip across the cogs when under higher tension.
Probably best to change both together on any chain used for more than a year of daily riding. 

The advanced riders solution to a broken chain is to carry a special link that can be fitted and removed without tools, although you prob need a special chain tool to remove bits of broken link.
The link comes free with most modern chains.


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## vickster (22 Jul 2019)

I always get the two changed together. Saves me time and hassle in the long run and the cassettes on the bikes that get ridden most are under £25 online. Order together, hand over to LBS, job done. Once a year if that once the chain is properly worn and beginning to skip. Costs about £50 all in


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## Paulus (22 Jul 2019)

Generally yes, it is best to replace a worn chain and cassette at the same time. You can sometimes get away with only the chain, but at some point the chain will start to slip on the cassette and then you will have to replace it anyway.


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## JuliaT (22 Jul 2019)

bigjim said:


> Depends how worn the old chain is. The chain has usually had to be pretty badly worn to require a cassette change. Also a chain snapping is not a sign of a worn chain. It's quite a rare occurrence. Were the gears skipping before the chain broke? I'd be tempted to fit just the new chain. You will soon know if the cassette needs changing as the gears will start skipping about. So. he's wrong. They don't always have to be changed together at all. Change chains early enough and cassettes will outlast quite a few chains.



I honestly don't know how used they are/were, I bought the bike second hand last year and during the service they told me they were fine. This year in the service they told me the chain might need to be changed at the end of the season. The gears were not jumping, actually they worked beautifully (in my opinion). I guess I will follow your advise, leave the old cassette and if it starts skipping and jumping will replace it. Thanks!


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## JuliaT (22 Jul 2019)

johnblack said:


> You don't have to, but if your chain and cassette are the same age and the chain is worn, changing the cassette isn't a bad idea, it shouldn't cost a great deal, depending on what groupset your using obv.



I honestly don't know how old any of them is, as bought it second hand. But he told me the difference was from 20 (chain) to 80£ (chain and cassette)


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## Paulus (22 Jul 2019)

JuliaT said:


> I honestly don't know how used they are/were, I bought the bike second hand last year and during the service they told me they were fine. This year in the service they told me the chain might need to be changed at the end of the season. The gears were not jumping, actually they worked beautifully (in my opinion). I guess I will follow your advise, leave the old cassette and if it starts skipping and jumping will replace it. Thanks!


An old worn out chain can still work fine with a worn out cassette, as they wear out at the same time. If the cassette is shark toothed a new chain, which has perfectly round pinions will not fit the teeth on the cassette.


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## JuliaT (22 Jul 2019)

Ian H said:


> Cassettes wear as the chains wear, and fitting a new chain to an old cassette will often result in the chain slipping on some sprockets. Did he ask you how far you'd ridden on the current chain/cassette, or measure the wear on the snapped chain?


 He did ask, but I have no idea and he couldn't measure it bcos the old chain is in a bin where it broke... I guess he was giving me a safe advise


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## JuliaT (22 Jul 2019)

MichaelW2 said:


> If you change your chain before it becomes to worn, you can use the old cassette. Further wear will result in sharks teeth profile wear in the cassette. The old chain will work but a new chain will slip across the cogs when under higher tension.
> Probably best to change both together on any chain used for more than a year of daily riding.
> 
> The advanced riders solution to a broken chain is to carry a special link that can be fitted and removed without tools, although you prob need a special chain tool to remove bits of broken link.
> The link comes free with most modern chains.


That's quite interesting! I'll check how to do that in case this happens again. Thanks!


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## vickster (22 Jul 2019)

JuliaT said:


> I honestly don't know how old any of them is, as bought it second hand. But he told me the difference was from 20 (chain) to 80£ (chain and cassette)


£60 extra for cassette and fitting sounds a lot? What groupset is it?
If you only change the chain, you may hasten it’s demise on a worn cassette but up to you. It’ll just mean another £20 potentially but you could the. source the parts cheaper online and ask a shop to fit (mine only charges another fiver if I get the parts)


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## Ian H (22 Jul 2019)

JuliaT said:


> He did ask, but I have no idea and he couldn't measure it bcos the old chain is in a bin where it broke... I guess he was giving me a safe advise



Well yes, it saves the possibility of you having to make a second visit.


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## JuliaT (22 Jul 2019)

vickster said:


> £60 extra for cassette and fitting sounds a lot? What groupset is it?
> If you only change the chain, you may hasten it’s demise on a worn cassette but up to you. It’ll just mean another £20 potentially but you could the. source the parts cheaper online and ask a shop to fit (mine only charges another fiver if I get the parts)



I am not saying it is cheap/expensive because have never bought it, so don't have a reference to compare. I am concerned as that is not my regular bike shop and in some areas of London they try to scam you easily, that's why I was asking. I don't know the chain he is putting, but I saw the cassette was shimano of 9 speeds...nothing more that I know. I will probably keep an eye on it and will take it to my trusted regular bike shop. But thanks!


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## bigjim (22 Jul 2019)

I buy 8 or 9 speed chain and cassettes for about £20 total. It's an easy DIY job to fit them yourself if you have the simple tools needed. It might be worth buying these if you see yourself as a regular cyclist. The cost of the tools are probably less than the labour charge for one change. There are lots of YouTube videos that talk you through the process.


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## Paulus (22 Jul 2019)

JuliaT said:


> I am not saying it is cheap/expensive because have never bought it, so don't have a reference to compare. I am concerned as that is not my regular bike shop and in some areas of London they try to scam you easily, that's why I was asking. I don't know the chain he is putting, but I saw the cassette was shimano of 9 speeds...nothing more that I know. I will probably keep an eye on it and will take it to my trusted regular bike shop. But thanks!


Shimano and KMC chains are quite cheap and will work fine.


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## Milkfloat (22 Jul 2019)

A good tip to check a cassette with a new chain, before it starts skipping, is to crouch by the side of the bike pull the bake brake lever and turn the pedals. If the chain is riding up/moving a lot on the cassette then it is worn.


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## mjr (22 Jul 2019)

Reasonable precaution IMO. He's seen the cassette, we haven't. A broken chain is basically a flail for its last few seconds and could even have done some damage he's spotted.

As for replacement cost, if he's replacing like for like, some of the Shimano 9 speed cassettes are damned expensive. If you ask and don't mind slightly different gearing, there may be a cheaper option. Remember that it's not only the parts but fitting labour too, though, although it isn't a long job.


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## mjr (22 Jul 2019)

Milkfloat said:


> A good tip to check a cassette with a new chain, before it starts skipping, is to crouch by the side of the bike pull the bake brake lever and turn the pedals. If the chain is riding up/moving a lot on the cassette then it is worn.


Can anyone think of a test before fitting a new chain, though? The £3 0.75/1.0 chain check tools seem as good as I've heard: the more easily the .75 drops through, the more likely a new cassette is needed. If the 1.0 drops through, it's a cert.


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## Milkfloat (22 Jul 2019)

mjr said:


> Can anyone think of a test before fitting a new chain, though? The £3 0.75/1.0 chain check tools seem as good as I've heard: the more easily the .75 drops through, the more likely a new cassette is needed. If the 1.0 drops through, it's a cert.



Measuring the chain is easy and in this case the change has been done already. I agree a chain checker tool is invaluable to me.


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## Vantage (22 Jul 2019)

I hear the so many links to the 12" mark on a ruler is far more precise.


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## mjr (22 Jul 2019)

Vantage said:


> I hear the so many links to the 12" mark on a ruler is far more precise.


It probably is, but requires the chain to be placed under tension, the ruler to be held steady against it and the maximum measurements to be remembered or maths to be done, like is it time to replace at a sixteenth of an inch over or an eighth?  Checkers are a much easier test for non-mechanics.


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## johnblack (22 Jul 2019)

Sram 9 spd and chain on amazon at £20ish if bought together.


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## Sharky (22 Jul 2019)

JuliaT said:


> He did ask, but I have no idea and he couldn't measure it bcos the old chain is in a bin where it broke... I guess he was giving me a safe advise


Worth keeping the old chain, so you can get the length of the new chain exactly the same. That is if everthing was working smoothly.

Worth also, mastering the DIY needed and carrying a chain splitter tool and a quick link with you, so you can do roadside fixes to get you home.


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## JuliaT (22 Jul 2019)

Sharky said:


> Worth keeping the old chain, so you can get the length of the new chain exactly the same. That is if everthing was working smoothly.
> 
> Worth also, mastering the DIY needed and carrying a chain splitter tool and a quick link with you, so you can do roadside fixes to get you home.


Yes...I just learned that....well, I'll know better next time!


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## PaulSB (22 Jul 2019)

On both my winter and summer bikes I change cassette and chain (probably twice) annually. I like the reliability and security of knowing my drive train is in very good condition.

The only two mechanical things I can reliably do on the road is change a tube or fix a chain. On a well maintained bike that should be all you need. Practice at home, carry the tools and you will be fine.


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## Ming the Merciless (22 Jul 2019)

My cassettes last about four chains. Get a chain wear tool and change before it leads to a worn out cassette.


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## ianrauk (22 Jul 2019)

PaulSB said:


> On both my winter and summer bikes I change cassette and chain (probably twice) annually. I like the reliability and security of knowing my drive train is in very good condition.
> 
> The only two mechanical things I can reliably do on the road is change a tube or fix a chain. On a well maintained bike that should be all you need. Practice at home, carry the tools and you will be fine.


I do the same. Once a year, new cassette and new chain. I just cant be bothered with the faff of measuring chains v cassettes.


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## 12boy (29 Jul 2019)

I thinks its a good idea to change my 12 tooth Brompton sprocket along with the chain as it is heavily used since little wheels must turn many more revs. Bikes with multiple speeds sprockets last a lot longer. As far as master links go, they are chain specific, so a 9 speed chain may take a narrower master link than a 7-8. Most LBS can sell you links without a chain, and a couple in your carry-with tool kit are nice, in case you drop and lose one while fixing a chain. While very useful, they. can be tricky in cold, wet or dirty conditions whereas a good chain breaker tool will always work, although you may have to wiggle the links involved sideways to loosen them once put together. Like flat tires, there is a big difference in crouching in the rain or snow to fix something and doing it in a warm, dry workplace. Definitely, if you go the master link route, practice taking one apart a few times at home.


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## Ticktockmy (30 Jul 2019)

JuliaT said:


> Hi all,
> 
> I am a beginner so I have no idea... My question is... is this for real or is he trying to scam me? If I have to change the cassette I will do it, no problem, but this sounds weird to me...
> 
> Thanks!


During the 40 odd years I have been cycle touring and Mountian biking I have never broken a chain (fingers crossed) however I know a lot of beginners that have, in the main it seems to be using the wrong gears, like standing on the pedels to flog up hill in to high a gear , one of the reason we have gears is to relieve the strain on us and on the drive system. 

Without knowing what state your chain or cassete was prior to the chain snapping its hard to understand what has caused your chain to snap. I try to get at least 3500 miles out of a chain and cassette before replacing them together depending on which conditions the bike is being used in.


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## boydj (30 Jul 2019)

If you commute in all weathers you'll break a chain eventually, even if you check and clean your chain regularly - I've done it twice. You should check your chain for wear frequently and change it when required to get the maximum use out of your cassette.


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## Supersuperleeds (30 Jul 2019)

ianrauk said:


> I do the same. Once a year, new cassette and new chain. I just cant be bothered with the faff of measuring chains v cassettes.



Same here new chain and cassette every time, though I only tend to change when I start getting problems


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## Racing roadkill (15 Aug 2019)

JuliaT said:


> Hi all,
> 
> During my commute this morning my chain snapped. I took the bike to the shop as I had no tools or knowledge on how to replace it (specially in the middle of the street and having a meeting in the morning).
> The guy in the bike shop told me that, as I through away the snapped chain he would have to change the cassette. That they have to be replaced together... if not I will have problems with the new chain...
> ...


 ‘Best practice’ dictates that he’s right. The chain and cassette ‘mesh’ in unison. Replacing one without the other, simultaneously, can lead to the new chain slipping, under high force. However, in reality, unless the chain and cassette that were originally on were worn out, you could get more than one chains worth out of each cassette.


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## Apollonius (15 Aug 2019)

I don't see how the shop could do anything other than change both chain and cassette. You only know your cassette is worn out when it slips with the new chain. The shop could not send a customer away with the chance of that happening. 

Obviously, for a rider who knows what to do, changing a chain and cassette is a simple routine task, but if you don't know how to do it and don't have the tools, then you have to pay up. Might be an incentive there to learn, invest in the tools, and progress as a cyclist.


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## hawaiiguy (20 Aug 2019)

Ticktockmy said:


> I try to get at least 3500 miles out of a chain and cassette before replacing them together depending on which conditions the bike is being used in.



With close to 15k miles on my bike (Giant Defy 5) without a change of chain or cassette, I think it's time. I've done it before on my previous bike (Giant Escape 3) but may need different tools to remove the cassette from the current one. I'll report on how it goes later.


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## andrew_s (23 Aug 2019)

JuliaT said:


> During my commute this morning my chain snapped.
> The guy in the bike shop told me that, as I through away the snapped chain he would have to change the cassette. That they have to be replaced together... if not I will have problems with the new chain...
> I am a beginner so I have no idea... My question is... is this for real or is he trying to scam me?


If a chain breaks, the possible courses of action are...
1) Remove the remains of the broken link with a chain tool and fit a quick link
2) Measure the chain, and if it's not too worn (up to 0.75%), just fit a new chain, otherwise (4)
3) Fit a new chain and take a chance on the chain slipping on the cassette. If it does slip, there's a chance you could crash as a result.
4) Fit a new chain and cassette.

If you've thrown away the broken chain, (1) and (2) aren't possible, and a responsible bike shop won't do (3), which leaves what happened - a new chain and cassette.

Causes of broken chains I've come across are...
1) Manufacturing defect. No personal experience, but I've seen the photos of the broken chain cleaned and coiled up to show half a dozen other links cracked but not yet broken (cracks in outer side-plate from the pin outwards).
2) Badly joined. Rare now most chains are joined using quick links.
3) Trying to change gear whilst exerting maximum push on the pedals. Back in the day, you'd just get scraping noises and no change if you tried to change whilst pushing hard, so you learnt to change whilst still pedalling reasonably briskly, and to ease off the pedal pressure during the change, but since Mr Shimano made changes under pressure work (mostly), many more recent cyclists expect to be able to change however hard they may be pushing on the pedals.


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