Cassette wear - how to check

cossyrush Posts: 43
edited June 2019 in Workshop
Some advice please.
How do you determine if a cassette needs replacing during a service on a bike with unknown history?
If you measure the chain and it’s past 0.75 then you change it.
But what about the cassette?
I know you can ride it and see if it skips, but is there a way to check it without having to ride it.
And I know the general rule of thumb would be 3 chains to one cassette, but if you don’t know the number of chains it’s had, or it’s just on one chain with more than 1mm wear.

What is the Rohloff tool like?
Is that how bike shops determine if a new cassette is needed.


  • timothyw
    timothyw Posts: 2,482
    I suspect shops always say you need a new cassette because that is how they make money.

    Would be interested to hear an answer on this one but I think it comes down to skipping chain - and that isn't definitive as a somewhat worn cassette will often skip for the first thirty miles or so then be fine, once it has bedded in.
  • cossyrush
    cossyrush Posts: 43
    Yes my thoughts exactly, and if I’m fixing a mates bike I want to check all the bits order what is needed, get the job done and go riding.
    Don’t want to fit a new chain and then say give it a go it might be ok.
  • Alejandrosdog
    Alejandrosdog Posts: 1,975
    Ride it, if it skips under load it needs replacing

  • mankybianchi
    mankybianchi Posts: 117
    TimothyW wrote:
    I suspect shops always say you need a new cassette because that is how they make money.

    From a shop perspective, it's not particularly making money but more about guaranteeing the work. If the customer hears that after just a chain being replaced it might slip on the cassette but it then again it might not, then that's not a very inspiring sounding assessment.

    As a customer, I'm sure most would prefer to leave the shop without being told your chain may or may not slip so you might have to come back.
  • cossyrush
    cossyrush Posts: 43
    Totally agree, so how does a shop determine if the cassette needs to be changed.
  • itboffin
    itboffin Posts: 20,052
    i keep meaning to draw an outline stencil of my next new cassette then when i do a deep clean i.e. once before the end i can compare it to new.
    Rule #5 // Harden The Feck Up.
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  • mankybianchi
    mankybianchi Posts: 117
    cossyrush wrote:
    Totally agree, so how does a shop determine if the cassette needs to be changed.

    Well they could simply set a policy such as if the chain gauge shows 0.75% wear then change the chain* and if it shows 1.0% then change both.

    The cassette at this stage may not show particular wear or it may only be worn on certain sprockets.

    *This is where the customer knows that this is the first chain to have been replaced with this cassette. Clearly a chain at 0.75% wear on a cassette which has had replacement chains before is a different case.
  • cycleclinic
    cycleclinic Posts: 6,865
    You cant see cassette wear unless it's very worn but experience shows it.

    We dont change cassette for the sake of it but if a bike come in like today with a well worn chain we know the cassette is toast. If the bike is well maintained and we see it regularly then the chain gets changed and not the cassette.

    The 0.75% limit is junk. If the chain is changed at 0.75% but the cassette is kept then a test ride is need with 800w sprints to find out of the chain skips. To do that in all gears is not practical . The risk of the bike coming back is too great so cassette get changed of we are unsure of the cassette will be o.k. you see it might be fine initially but after 500 miles it might not be. Skipping might start or the shifting gets iffy. That the shops reputation right there going up in smoke.

    One of own bike with a campag 11 speed 12-27t chorus cassette had it chain changed in time or so I thought (kmc 11-93 changed at 0.75% wear). All looked well until I shoved out power (500+W) I and the chain skipped on the 12t cog. That was the second ride with the new chain however with so many bikes I can not remember how old the cassette is. I think its seen more than one chain. The moral is you cant see cassette wear and while for our own bike we will try and see good results cannot be guaranteed. All you have to do is leave a smidge too long and ride that small cog alot and the cassette. is ruined.

    So forgive shop for playing it safe. In our experience changing the cassette and chain together is the safe thing to as most of the time whe we see a bike the smchain has been on there for some time. You keep the cassette if you change the chain early. 0.5% wear is the limit to get 3 or 4 chains to the cassette. Campag have a different measure using a vernier. Change cassettes early and the cassette survives for many chains.
    At 0.75% it can be toast even after one chain.

    In my experience once skipping starts its does not go away. If it does go away it has not. All that has happened your chain has worn prematurely on the worn sprockets so now you have a worn chain on a worn cassette.

    However if we change the cassette at 0.5% wear the customer thinks we are having them on.

    Also mileage is not a good indicator. In winter I dont even get 1000km out of a good chain on the road. In summer I can get 3000km from a chain if it's a campag effort. Kmc last 2000km at best. Power, the gear you ride in (small cog users get more chain and cassette wear more quickly) and conditions all affect wear.

    The best way of getting the most from a cassette is to start with a cassette and every 1000km change the chain until you have 4 chains. Keep the old chains and rotate putting the first chain after the fourth is done. That way very long cassette life can be achieved but it too much effort for me. 23 bikes means nearly 100 chains on the go. No thanks. -wheel building and other stuff.
  • cossyrush
    cossyrush Posts: 43
    Thanks for the detailed answer Malcolm.