Does this chainring need replacing?
 

Hi, My son has just bought a 2nd hand bike to use on a smart trainer. The cogs look a bit worn on the large front chainring. Will it need replacing soon?
https://cimg1.ibsrv.net/gimg/bikefor...772d6abbba.jpg
https://cimg0.ibsrv.net/gimg/bikefor...eeda0eb0c2.jpg

Is the chain skipping? Every chain ring will need to be replaced eventually if it is used .... (as in, "put to use, ' not "purchased from a prior user,") so yes, in time, it will need replacement. I wouldn't replace a chain ring if it was still performing well, though. If the chain skips off or slips ... get a new right, right away.

Of course, I could be wrong.

No. The teeth aren’t supposed to be the same all the way around. Some of the teeth will look flatter than the others but that is a design feature that improves shifting. Your chainring looks fairly fresh and serviceable.

Thanks, the big chainring looks a lot more worn than the smaller one. But it's good to know it doesn't need replacing yet as it's not slipping.👍

As cyccommute said, it's probably not worn at all. The big ring is deliberately designed to have shorter teeth in some sections to facilitate easy shifting up from the small ring.

When I worked in bike stores, customers would come in to ask about/complain about the short teeth on the big ring at least a few times per week. We'd just walk them over to the display bikes and point out that the big rings on all the brand new bikes had teeth that looked exactly the same as their ring.

tooth 'shape' is hard to judge on modern chainrings, some have flatten top, others have a sharkfin shape which appears 'worn' but isn't.
way we had checked BITD, with chainline tight on chainring and all the way through jockeywheels and middle cog - pull/lift chainlink off of chainring at the point where a horizontal line bisects the Bottom bracket. This is the point where the chainwrap on the ring is the tightest.
If the chain lifts so much that the chainring teeth are greatly/more than fully exposed - ring may be worn... Total Judgement call !!! I'm not acquainted with any 'hard measure'.

https://cimg7.ibsrv.net/gimg/bikefor...12d49dc9c6.jpg
This one looks ok.
IMPORTANT Conidtions
Chain must be in almost new or new condition. Worn chains first thing to check (best with a Park Tools chain checker (there are many poor/cheap substitutes which aren't accurate).
The CC3 and similar from Park Tools are great.
Used Bike? Always check the chain before using...
My visual assessment (which may be wrong) is the chainring looks good.
Ride On
Yuri

One of my C Record cranks just gave you the side eye...

Does it have Shimano Sora rings?

Not sure, the bike is 2nd hand, the groupset is Sora unless the chain rings have been replaced?

No, I drilled out the rivets on the cheapest Truvariv I could find and used that... :)

Your crank is Sora and so are the rings. My (joking) question was addressed to wheelreason.

Since you weren't referencing a set of Sora cranks/rings, the point you were attempting to make with your "side eye" remark is unclear.

lol...it's fine