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Old 06-28-07, 05:53 AM   #1
jim p
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Do you rotate your chainrings?

Probably for most of us this occurs only when we pedal. I took an old chainring off a bike because I was considering putting it on another bike so that I could change the gear ratios. When I looked at the Aluminum chainring I noticed that the teeth were worn on sections and that on other sections the teeth looked like they were almost new. This uneven wear was probably caused by mashing as opposed to spinning. Any way it would appear that rotating the crank arms 90 degrees maybe each time we replace our chains might even the wear out on the rings. I know most people just buy a new bike when the chain needs to be replaced.
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Old 06-28-07, 06:11 AM   #2
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Quote:
Originally Posted by jim p
I know most people just buy a new bike when the chain needs to be replaced.
Well, after 25 years as a mechanic I never saw that!

Chainrings these days are position specific. Your shifting may be adversely affected if you move them around. Frankly, if you keep your chain and cassette/freewheel combination fresh, and aren't a masher, your chainrings can go many years...
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Old 06-28-07, 06:33 AM   #3
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The same A-ha moment the Biopace ring desinger had, I'm sure. Besides shift issues, another thing to watch for - if you rotate your big ring the pin that prevents your chain from wedging in the crankarm will not be in the right position.
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Old 06-28-07, 07:06 AM   #4
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Quote:
Originally Posted by jim p
Probably for most of us this occurs only when we pedal. I took an old chainring off a bike because I was considering putting it on another bike so that I could change the gear ratios. When I looked at the Aluminum chainring I noticed that the teeth were worn on sections and that on other sections the teeth looked like they were almost new. This uneven wear was probably caused by mashing as opposed to spinning. Any way it would appear that rotating the crank arms 90 degrees maybe each time we replace our chains might even the wear out on the rings. I know most people just buy a new bike when the chain needs to be replaced.
Are you sure you weren't just seeing ramped teeth instead of wear? What did the worn teeth look like compared to the others?
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Old 06-28-07, 08:19 AM   #5
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Years ago, before ramped and pinned chainrings and cogs, riders could reverse both the rings and cogs when they got worn so the new, unworn side of the teeth faced a new chain. The chain-drop pin was often part of the drive-side crank arm so it wasn't a problem.
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Old 06-28-07, 10:03 AM   #6
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I rotate my chainrings every time I turn the crank; doesnt everyone?
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Old 06-28-07, 10:12 AM   #7
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To sum it up:
If your components are post 80's the teeth are supposed to look different by design
You can't rotate your chainring 90 degrees unless your crank has 4 arms. Most have 5
Rotating a modern chainring will make the teeth pattern off and the chain pin in the wrong place
The only proper way to rotate a modern chainring is by pedalling on the bike

btw, if you have a modern bike, don't freak out if your cassette cogs looks out of alignment or out of true.
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Old 06-28-07, 02:18 PM   #8
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Quote:
Originally Posted by rmfnla
I rotate my chainrings every time I turn the crank; doesnt everyone?
EXACTLY!
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Old 06-29-07, 05:34 AM   #9
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The chainring was definately worn. With square taper cranks the crank arms could be moved 90 degrees on the spindle. If there are specific orientation requirements for newer rings then this could not be done. This was just an observation that got me to wondering if anyone else had done this before.
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Old 06-29-07, 12:48 PM   #10
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Ummm, rotating the cranks on the bottom bracket spindle won't change the chainring's location in relationship to the crank arms, so you just defeated your whole purpose with that one.
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Old 06-29-07, 02:55 PM   #11
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Quote:
Originally Posted by rmfnla
I rotate my chainrings every time I turn the crank; doesnt everyone?
You win insightful post of the day award.
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Old 06-29-07, 02:57 PM   #12
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Quote:
Originally Posted by HillRider
Years ago, before ramped and pinned chainrings and cogs, riders could reverse both the rings and cogs when they got worn so the new, unworn side of the teeth faced a new chain. The chain-drop pin was often part of the drive-side crank arm so it wasn't a problem.
Yeah you're talking about reversing... he's just talking about unbolting it and then spinning it randomly and bolting it back on without reversing. The OP must be really mashing if you see a really marked difference between sections of chainring.
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Old 06-29-07, 03:20 PM   #13
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Originally Posted by operator
The OP must be really mashing
Ooh, he just called you a masher. You gonna take that from him?

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Old 06-29-07, 04:45 PM   #14
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Yeah I did sort of blow it by just rotating the cranks on the spindle. So if anyone wants to try to even out the wear they would have to unbolt the chainrings and move them say one spider arm and then bolt them back down.

This is a soft aluminum chainring which is worn and mashing is probably the reason it is worn the way it is. It is also interesting to look at the ring and notice that one point is worn more than the point 180 degrees from it. I guess that one leg is stronger than the other.

It is interesting that no one has observed this before.
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Old 06-29-07, 05:28 PM   #15
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Nah, it's certainly something that happens. Most people just haven't looked closely enough at their chainrings. The part that's the most worn is about 90-degrees after the crankarm when you've got the post force on the downstroke. Even if you're a spinner, this spot (and the opposite side) will have the most wear.

Due to the fewer teeth on the small chainring, it wears out much faster. I had a skipping-chain issue where it would ride up on the teeth when I was climbing out of the saddle with a lot of force on the pedals. Rotating the chainring 144-degrees to a newer section solved that problem completely.

As for needing pins to prevent the chain from wedging between the chainring & crankarm, that's a FD adjustment. Calling the pin a "feature" is like saying that you need heavy-duty steel bumpers on your car because you tend to rear-end people all the time...
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Old 06-29-07, 07:55 PM   #16
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Quote:
Originally Posted by rmfnla
I rotate my chainrings every time I turn the crank; doesnt everyone?
No matter how bad my day is, I can always get a laugh with a well crafted reply.
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Old 06-29-07, 09:51 PM   #17
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Did we ever determine what vintage your chainrings are? We haven't addressed the fact that modern rings have different patterns on the teeth (including 180 degrees around) as part of their design to aid shifting.
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Old 06-29-07, 11:07 PM   #18
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Quote:
Originally Posted by urbanknight
Did we ever determine what vintage your chainrings are? We haven't addressed the fact that modern rings have different patterns on the teeth (including 180 degrees around) as part of their design to aid shifting.
While the upper teeth-profile may be different to help shifting, such as lower tops to help the chain ride over, the valley where the chain rests is still perfectly round. A worn spot would show up as an ovalized valley with a hook recessed area on the leading side of the teeth.

I've figured out why the chainring was more worn out on the right-side downstroke. It actually doesn't have much to do with uneven leg-strength, but from crank-flex. The left-side crankarm transmits its torque through the spindle and that force shows up at the centre of the spider on the right side. This results in even force spread out on each of the spiders and the chainring experiences force inline with the plane of the ring. However, the right-side crankarm gets twisted due to the offset pedal transmitting force from the outer end of the crankarm. This distorts the spider and the chainring is bent outwards slightly where the chain rides, thus causing more wear.
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Old 06-29-07, 11:21 PM   #19
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I never thought of that. Makes perfect sense, though.
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Old 06-30-07, 02:41 AM   #20
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Thanks Danno. You have put even more thought into this than me and you used it to solve a chain skip problem. Now all the ocp's wont be able to ride until they inspect and reposition their chainrings.
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Old 06-30-07, 07:29 AM   #21
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I "FLIP" the chainring on my singlespeed.
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Old 06-30-07, 08:06 AM   #22
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Nope, I just replace them as they wear out.
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