Are your chainrings and cassette worn? Here's how to tell when they need replacing

Is a parking lot the same as a car park ?

I have never experienced a chain breaking, and that's after several decades of the deprecated practice of pushing any old pin out and pushing it back to rejoin. I have now moved on to removable split links, which have facilitated my present chain/ cassette/ chainrings policy which I am applying to the steel gravel bike of October 2019. I was determined to wear out the originals systematically, before installing the replacements I bought at the same time. I must have done over 12000 miles with four chains, replacing them when they reach Level 1 wear on the Rohloff chain tool. I'm now going back to each chain in turn to wear them to Level 2+, when they're binned as has just happened to Chain 1. It's all going well so far, but the crucial question is whether the cassette and small ring (32- wish it was steel!, replacements are 46-30) will last through the remaining 3 chains.

Some old school bike techs advocate leaving a chain on till it drops approach - I know a tech at a LBS who said that to me a few weeks ago.

Firstly, a worn chain loses strength. These are not the chains of our youth which were heavy but lasted for the life of the bike it seemed, but an old chain beyond its design life is a chain waiting to break. The most I got out of a 10 speed chain on a road bike while within the wear guage tolerance was about 3,000 miles. I reckon a cassette lasts for about 3, sometimes 4 chains, so about 10,000 miles, but I could always tell the difference when renewing the cassette. 11 speed chains seem to last for about 2000 miles.

When a chain is not worn, it doesn't cause much wear, but as it wears, the damage a worn chain produces increases, as the chain bears all the stress on a single tooth, which causes more wear (a new drive chain bears the load across several teeth of chain ring and cassette).

Once a cassette (and in extreme cases, chain rings, which have more teeth to spread the wear over) has been over-worn, a chain simply does not fit, so you have no choice but to change the cassette when changing the chain. 

On mountain bikes, almost invariably the top gear, the 11 tooth cog, wears, as they are low geared and riders ploughing along the road invariably end up grinding along in top - very few teeth, high pedalling force, rapid wear. Some cyclists stick in a couple of gears, so end up with a single cog worn, hence the skipping in one gear. I would always suggest using the full range of gears not just to save your knees but also to save wear. Spinning also produces less wear - going up a hill at a high cadence requires less force through the drivetrain - grinding up a hill is putting a lot of pressure through the chain and cogs and will create more wear even though the chain and cogs are being worn fewer times.

Worn chain rings are rarer because they spread the load across far more teeth, but they do wear and eventually become unusable. Aside from chain suck (chain refusing to drop off the chainring at the bottom), chain rings can also cause slips. 

Slips and snaps mean a good chance of falling off. So, I would say, change the chain according to a wear gauge, keep it clean (but avoid using degreasers that potentially stay in the chain and damage the oil applied afterwards) and that will be the best way to have a reliable, safe bike at minimum cost (that is you can run a bike more cheaply, but it won't be safe to ride for a higher proportion of its life).

I'm currently avoiding sixth gear on my cassette (last week or so): if I'm in middle-chainring-and-sixth-sprocket and I stand on the pedals to either accelerate away or go up a hill then it skips.  I suspect I might need to change the cassette soon... 

Quote:

chainring teeth slowly take on the shape of a shark’s fin in use.

Is a shark's fin a different shape when it's not in use?

Old chainring cannot cause a skip. If it locks it locks. It will cause delay in shifting and rubbing during change from small to large ring as the tiny chain grips below the chain teeth are not sharp enough to lift the chain. Also, it will cause premature chainwear.

Old cassette on the other side can immediately be identified as the shifting will fail - regardless of chain age and adjusting the barrel adjuster will make thing worse.

A steel chain does not stretch, it does wear, but it does not stretch.  What is perceived as stretch is simply the pins and bushings wearing and gives the appearance of stretch.  

Anybody know what the cassette pictured above is? (between next down from the chain checker)

That cassette looks like an accident waiting to happen.

Here's a tool for checking cassette wear.

Then strip it down and sell those middle gears to a ninja... perfect throwing star...

Carlos does like a nice straight chainline judging by the way he sits in the middle gears on his block! Nicely done sir!

PP

I don't have this problem - hub gears and belt drive on my commuter.

For me when a chainring has gone too far, the skipping is worse, properly dangerous, especially when trying to pull away from the lights or at junctions.

And my goodness Carlos, I didn't think you could stretch and wear a cassette quite that much.  Obviously still rideable, up to that point, otherwise you couldn't have acheived that.

Are worn chainrings likely to cause skipping under load in the same way a worn cassette would?

I have an old Dawes MTB which started skipping when I replaced the worn chain.  I got the cassette replaced which improved things a bit but it still skips.  I can see two scenarios.

Whole drivetrain needs to be replaced as it was all worn out so time to get a new chainset.  Or.
The new chain is now damaged because it was used on a worn cassette.

Or both...