Chain & Cassette Replacement

trigger13

Hi,

I just took my bike in for looking at as the chain was jumping when pushing hard and it wasn't down to needing to adjust it.

One of the things they said is that because the chain is stretched, I need a new one, fair enough. But I apparently also need a new cassette because it won't sit right with the old one. This doesn't seem right to me, I thought chains were universal? Getting the same speed cassette etc. just replacing dodgie parts.

Hoping to get it under warranty since it's under a year old but even if I don't have to pay for it I'd like to know if I'm been taken for a ride (sorry for the pun).

cooldad

Yep, new chain on an old cassette will likely jump - they wear together. So a new chain won't mesh with a worn cassette. But it depends on how stretched.
No way it'll be under warranty - it's wear and tear.

FishFish

I think that the mechanic is right. If the chain is worn then what happens is that the rollers abrade to the extent that the chain appears to stretch. That is ok for a while and if you detect wear and replace the chain before the wear is too extensive then you do not need to replace the cassette. There is a very simple tool for measuring this chain stretch. If you wait until the chain is too worn then you will need to change both the chain and the cassette or you will have problems with skipping gears , ghost shifting and accelerated wear on the new chain from an old and worn out cassette. In a car you will not get tyres under warranty - ditto chains. Good idea to buy a chain stretch tool and use it to diagnose when to change the chain and cassette - which is a fairly easy task.

FishFish

trigger13 wrote:

Hi,

I thought chains were universal?.

and btw chains are not universal - they are 7/8 or 9 or 10 and even 11 sped matching the number of gears on the cassette and they differ in price depending on quality or what the mfg can get away with.

njee20

IME a chain and cassette have to be utterly utterly wrecked before they'll start slipping. That usually happens when you replace a part of the drivetrain (like the chain) and it doesn't mesh with the old parts.

Have you done a huge number of miles?

FishFish

Good point njee. My guess on the worn roller theory is that when you use the stretch tool it is over about 8 links and the prescribed limit for changing the cassette too is 1 mm stretch. This means that the rollers will sit lower in the cogs and so make it harder for them to come out of the cog when changing gear so ghost shifting arises. I have managed to get slipping on new chain and new cassette by bad indexing - but I know what you mean.

The Rookie

No, what happens is the chain is meant to engage with all the teeth it's sitting against, a chain that is longer (due to wear between pins and side plates, not the rollers wearing) will only engage with one tooth at a time so as it rolls off it it wears it when is shouldn't.

FishFish

Rookie - good analysis - can I try to paraphrase for clarity. It is the inside of the rollers that abrade the pins making the rollers looser and thus apparently extending the chain?

njee20

The Rookie is right, but as I said you need to be miles beyond 1% 'stretch' for that to happen. My winter road bike doesn't slip and you can see clear daylight between chain and sprocket, and I'm a relatively powerful rider. Change the chain and you'd not have a hope in hell, but it's fine while it's in harmonious shagged-ness.

The Rookie

FishFish wrote:

Rookie - good analysis - can I try to paraphrase for clarity. It is the inside of the rollers that abrade the pins making the rollers looser and thus apparently extending the chain?

No, the rollers run on a section of plate, not the pins, and any play of the roller on the bush sections will only increase chain length slightly when measured between two points, but not at all over it's entire circular length, it's the play at every joint that extends the chain length.

trigger13

Son of a witch Thanks for all the replies, learnt a few bits there! Understandable that you wouldn't get tyres and bits under warranty but wouldn't have thought the chain should have stretched >.> Oh well, see what happens!

Oh and I knew there were different size chains sorry, just meant that a chain for a 7 speed would fit all etc. Fingers crossed I can save some cash. Knew I should have taken up jogging....

The Rookie

trigger13 wrote:

wouldn't have thought the chain should have stretched .

The chain doesn't stretch (in the sense that any part gets longer), its the wear between the pins and plates and the resulting 'slop' in all the joints that results in it's lengthening.

Everyone uses 'chain stretch' but personally I hate it as a description, it's chain wear!

trigger13

I know what you mean, I'll try avoid the phrase in future :P