When to Replace MTB Chainrings?

[Mintman]

Hi guys, I need to replace my cassette and chain for my SLX 2x10 drivetrain. I should have replaced them ages ago so I'm worried the chainrings will have been worn down too much. Not the best pics attached but hoping to get your opinion on whether they should also be replaced.

 

Thanks for any assistance.

[madmarc]

From the pics that chain is clearly toast - the chain rings look like they need replacing as well. I would replace everything - Cassette - chain & chain rings

[Mintman]

Thanks Marc, I've managed to find both rings online and will just replace everything at the same time, as you suggested.

 

From the pics that chain is clearly toast - the chain rings look like they need replacing as well. I would replace everything - Cassette - chain & chain rings

[David Marshall]

I can't tell from the pics but here are some general tips for deciding when to change.

 

If you fit a new chain and the chain tries to "stick" to the ring rather than fall off as it leaves the ring it is time to change.  You can see this while the bike is on the stand.

 

On a triple the mid ring seems to be most used.  If you fit a new chain and get any chain noise when on the ring - time to change.

 

If you cross chain on the large ring and the chain tries to fall to the middle it is also a good indication of wear.

 

A worn chain will trash a cassette while the rings may not suffer as much for the following reason. 

 

When the chain enters the cassette it is under lower tension than when it leaves.  It enters under the tension of the derailleur spring and leaves under your crank power.  A worn chain elongates and as it pulls into the cassette the rollers are forced down the face of the cog with increasing tension and progressively grind a number of teeth on each rotation. This increases the space between the teeth so that when the cassette is shot a new chain will "jump" under power when it can't mesh properly.

 

At the other end the tension at which the chain enters the ring is much higher than when it exits. Within the first couple of teeth a worn chain relaxes into the correct length and sits in the space between the teeth.  The number of teeth exposed to wear is considerably less than on the cassette and hence rings do not wear as fast.

 

Changing all the rings is almost as expensive as a new crank so if you are planning an upgrade this could be the time.  If the BB needs to be replaced as well  you could also consider a downgrade to a new cheaper crank/bb combination - for a similar price to the rings.

[Mintman]

Thanks for the thorough feedback, Dave. I had already bought a 10 speed cassette and chain so I wanted to try find the cheapest option to get the bike up and running smooth. Otherwise I would have gone the upgrade route. I managed to find both SLX chainrings for a total of R499 so it worked out in the end. Not sure whether my bottom bracket will need replacing though.

 

 

I can't tell from the pics but here are some general tips for deciding when to change.

 

If you fit a new chain and the chain tries to "stick" to the ring rather than fall off as it leaves the ring it is time to change.  You can see this while the bike is on the stand.

 

On a triple the mid ring seems to be most used.  If you fit a new chain and get any chain noise when on the ring - time to change.

 

If you cross chain on the large ring and the chain tries to fall to the middle it is also a good indication of wear.

 

A worn chain will trash a cassette while the rings may not suffer as much for the following reason. 

 

When the chain enters the cassette it is under lower tension than when it leaves.  It enters under the tension of the derailleur spring and leaves under your crank power.  A worn chain elongates and as it pulls into the cassette the rollers are forced down the face of the cog with increasing tension and progressively grind a number of teeth on each rotation. This increases the space between the teeth so that when the cassette is shot a new chain will "jump" under power when it can't mesh properly.

 

At the other end the tension at which the chain enters the ring is much higher than when it exits. Within the first couple of teeth a worn chain relaxes into the correct length and sits in the space between the teeth.  The number of teeth exposed to wear is considerably less than on the cassette and hence rings do not wear as fast.

 

Changing all the rings is almost as expensive as a new crank so if you are planning an upgrade this could be the time.  If the BB needs to be replaced as well  you could also consider a downgrade to a new cheaper crank/bb combination - for a similar price to the rings.

[DirtyDan]

Baby shark, doo doo doo doo doo!