Drivetrain

padyjoe

I have the following situation:
Sora chainring up front, I think with approx. 16k kms, I'm on my second set of cassette and chain (Sram PG950 and KMC X9), min. 8k kms on them. The chain is stretched at this stage, so time for a new one. New chain, not a bike! ;-)

Would you change the chainring as well this time? I have the above mentioned set ready and a Tiagra chainring. It'll be a colour mismatch, I know, as I have black cranks. But my brakes are going silver too. Thank you!

Type 17

That chainring looks pretty worn (teeth are starting to 'lean' - becoming angled, like shark's teeth). Even if the new chain doesn't skip on it, it will wear the new chain faster than if it was put on a fresh chainring. Time to change it...

magicbastarder

comparing the teeth on the inner and outer chainrings, they certainly do look like they have a different profile.

padyjoe

Thank you!
Yes, they do have a different tooth profile from new.
Clicky

I wonder is there a general rule of thumb for chainring wear? Or put the new chain on and look at it from the side how flush the chain sits on the ring?

CramCycle

padyjoe wrote: »

I wonder is there a general rule of thumb for chainring wear? Or put the new chain on and look at it from the side how flush the chain sits on the ring?

Basically, if it looks like yours, it has gone to far

Seriously though, I judge by looks, once the profile changes enough that you could tell at a glance, then it is time to switch.

padyjoe

Going by this thread, I'd say there's one more chain's worth left in it. I see shark fin on some teeth but not all of them showing it.
I reckon should start with the chain. If slips, casette goes in, if still not right, chainring then as it is the last to go. And you are right with the glance, I've casted it a good few times at it but not convinced 100% yet.

Type 17

If the you're going to fit a new cassette and chain, then you should change the chainring, as it's 80% worn out, and will wear out a new chain faster* than a new chainring would.

The reason that some teeth look worse than others is because the maximum chain-load applies to the chainring teeth which are at 12 o'clock when the left or right crank arm is at 3 o'clock (maximum power), so there will be two high-wear areas, and two low-wear areas (cranks at 12 & 6 o'clock).

*A new chain/chainring combo spreads the load out properly, say from 12 o'clock all the way around to 6 o'clock, so wear-per-link is minimised, but while a new chain on a part-worn chainring won't necessarily skip, the load will only be spread over, say, 12 - 3 o'clock, so the load-per-link will be more concentrated, and the chain will wear more quickly.

magicbastarder

padyjoe wrote: »

Going by this thread, I'd say there's one more chain's worth left in it.

that thread shows a chainring which is way past the point of replacement, so should not be used as a guide for yours.

why did you change your cassette after one chain anyway?
it's my understanding that you generally replace your cassette every three chains, and chainring every three cassettes, assuming you've been looking after them properly.

padyjoe

I had to change it because the new chain was slipping on the middle ring. I just started off back then, didn't look after the chain at all. The current situation is (might not able to describe it) when turning the cranks the chain goes like slack-tight-slack-tight. That's is a sign of chain stretch IMHO. A good chain should run smooth without noise.
TBH I'm not your usual suspect (not superhero either): threw the Defy's factory wheels out at 3k as it was popping spokes, a strong 36-spoke rims went in and I'm around 100 kgs and can sustain nearly an average 30 km/h on a good day. I'd say it's a good abuse to the drivetrain.