Chainring Where? No, Chainring Wear
See that little lip on one side of this chainring?
Years of hard riding on the same worn-out chain causes excessive friction, which leads the high-grade aluminum teeth of the chainring to squish out. This is also known as "mechanical fretting."
Friction did this.
Here's the worn chainring compared to a new, stainless steel chainring. You can also call it a "Chain Wheel" -- that's what the British say.
This last snap of the old chainring on top of the new one shows exactly how much material has worn down over time.
So, when you think your chainring might be worn out, use these images as a guide. If you see the little mushroom snares on the teeth, that's your sign.
When you get a new chainring, you need to know how many teeth the old chainring has, and the Bolt Circle Diameter (BCD), which is the way mechanics identify whether a chainring will fit on the crank. Also, if the chainring needs to be replaced, the chain and rear cogs will probably have to go as well. The good news is that aftermarket replacement parts, especially stainless steel aftermarket parts like that new chainring above, tend to last longer than the original equipment.
You can see on the cogset below, the rider's favorite gears have fretted over.
As a bonus, here's a super duper worn out chainring from the shop:
This chainring is made of cheaper aluminum than the one I used. Also, I believe the rider used a 1/2x1/8 BMX chain instead of the 1/2x3/32 chain the ring is made for. The wider BMX chain slops around and quickens the wear process. The reason wear is on both sides of the chainring is because at some point the rider turned his chainring around to even-out the wear on both sides of the teeth.
About the writer:
Scott Wilson is a BFF mechanic with a decade's experience in shops throughout the nation. He likes working on triathlon, road, and mountain bikes, and In 2015 he fabricated his first frame and fork at Doug Fattic's workshop. Check out his personal bike blog for more: bikeblogordie.com