straas
Matt
- Location
- Manchester
Stuck a new chain on and doesn't seem to skip at all, but only did a lap of the block.
Better image of the chainring attached.
Better image of the chainring attached.
In a situation like this, would rotating the chainring in the spider so that the worn area sits where your green circle is make sense, or is the chainring too far gone.OK, that photo reveals a lot more.
The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.
Have a look how much more the teeth are worn in the red area than green.
View attachment 507989
The shape of worn teeth represent shark fins (not shark teeth as often quoted, because shark teeth are symmetrical and chainring tooth wear is asymmetrical) with the sharp end pointing forward.
The is because the chain pulls on the teeth and wears pockets into the leading edge, eventually creating an area that's hollowed out, hence the shark fin shape that points forward.
What happens under these conditions is that the chain defaults to a position on the chainring that's not centre on the teeth but pulled back, with the centre of the chain bushing slightly behind the centre point of the tooth.
Eventually, this causes the new incoming tooth (as the ring rotates) to hit the next available bushing, instead of missing it. This creates a specific noise and a vibration. Both will be noticeable only to the mechanically sympathetic, mechanical-minded person.
It is time to replace your chainring.
OK, that photo reveals a lot more.
The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.
Have a look how much more the teeth are worn in the red area than green.
View attachment 507989
The shape of worn teeth represent shark fins (not shark teeth as often quoted, because shark teeth are symmetrical and chainring tooth wear is asymmetrical) with the sharp end pointing forward.
The is because the chain pulls on the teeth and wears pockets into the leading edge, eventually creating an area that's hollowed out, hence the shark fin shape that points forward.
What happens under these conditions is that the chain defaults to a position on the chainring that's not centre on the teeth but pulled back, with the centre of the chain bushing slightly behind the centre point of the tooth.
Eventually, this causes the new incoming tooth (as the ring rotates) to hit the next available bushing, instead of missing it. This creates a specific noise and a vibration. Both will be noticeable only to the mechanically sympathetic, mechanical-minded person.
It is time to replace your chainring.
Chainrings don't skip, unless the teeth are all completely gone. The front and back react completely differently to chain wear. As I said, the front's symptoms are a noisy, vibrating pedal action.Thanks for a very in depth explanation! I'll get a new one on order, I think my list is:
1 X 50t chainring
1x 32t 11sp cassette
1 X 11sp chain
2 X jockey wheels
Current plan is to ride it as is until it starts to skip, then change the lot. Sound sensible?
In theory, yes.In a situation like this, would rotating the chainring in the spider so that the worn area sits where your green circle is make sense, or is the chainring too far gone.
Not my experience:Chainrings don't skip, unless the teeth are all completely gone. The front and back react completely differently to chain wear. As I said, the front's symptoms are a noisy, vibrating pedal action.
In the rear it won't skate (let's use skate, rather than skip because skip refers to gear indexing problems) either, until you fit a new chain, which will then be mismatched with the sprocket.
The fact that it was quiet running means that it went way past the first stage of wear and you simply didn't even notice that it was running noisy and vibrating.Not my experience:
I have known a chain "skate" or "skip" on a badly worn chainring - but only under load and it was perfect smooth and quiet running the rest of the time ... and the rear shifting was perfectly OK because chain and cassette had worn together.
But isn't the set of teeth you've circled in green the 'powerstroke area from your left leg' and why would there be a different level of tooth wear between the peak torque from one side cf the other?The area I circled in red is the powerstroke area from your right leg.
The area in green is the dead zone.
Have a look how much more the teeth are worn in the red area than green.
Sharp. I attached a saved draft instead of the final one. The draft was a .png but saved a final jpg and I selected the wrong one.But isn't the set of teeth you've circled in green the 'powerstroke area from your left leg' and why would there be a different level of tooth wear between the peak torque from one side cf the other?
For reference - if anyone stumbles across this thread and has an identical chainring:
Despite other components being marked shimano 105, this chainring is not (I assume to keep costs of the build down), so you want to look for:
Shimano FC-RS500 - in this case the variant is the 50t-MH, and annoyingly is quite expensive!