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Grinding sound when standing and sprinting?

Old 02-08-15, 08:25 PM
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Alias530
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Grinding sound when standing and sprinting?

I have a cross bike that I just built a wheelset for. I got on the trainer earlier and noticed it did it on the factory wheelset too (that I'm now using with slick tires for road biking).

In my 3-4 smallest cogs if I stand and sprint, I get a grinding/crunching sound. What could this be?

Shifting is flawless, hangar is straight, and it does it on two different wheelsets/cassettes. The bike has maybe 400 miles on it and I maintain/clean it to an almost OCD level.
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Old 02-08-15, 08:44 PM
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won't venture a guess, but interested.
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Old 02-08-15, 09:00 PM
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First things first. Take a look at the crowns and sides of your tires, and check for any signs of rubbing. Sometimes sprinting deflect the bike enough for the tire to rub on the yoke of the trainer. If that's the issue, there should be visible marks or dust.

If what you're hearing is more by way of a whirring or buzz, it might be chordal action. We think of chains and sprockets as if they were ropes on pulleys, but that's not the reality. The chain runs on sprockets more like a rope running on a pulley that's a multi-sided figure having as many sides as the sprocket has teeth. That means the radius changes as the chain is pulling on a flat vs. a corner. So the chain is moving up and down X times per sprocket revolution, plus the sprocket speed (or chain speed) changes that many times also.

That produces vertical vibration, plus tension vibration and a noticeable grinding. This becomes more pronounced as the number of teeth are reduced, and would be very obvious if you imaging a sprocket having only 3 or 4 sides.

By analogy, imagine riding on wheels that have 32 sides, or 16 sides, or 8, 6, 4 or even 3.
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Old 02-08-15, 09:04 PM
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Originally Posted by FBinNY View Post
First things first. Take a look at the crowns and sides of your tires, and check for any signs of rubbing. Sometimes sprinting deflect the bike enough for the tire to rub on the yoke of the trainer. If that's the issue, there should be visible marks or dust.

if what you're hearing is more by way of a whirring or buzz, it might be chordal action. We think of chains and sprockets as if they were ropes on pulleys, but that's not the reality. The chain runs on sprockets more like a rope running on a pulley that's a multi-sided figure having as many sides as the sprocket has teeth. That means the radius changes as the chain is pulling on a flat vs. a corner. So the chain is moving up and down X times per sprocket revolution, plus the sprocket speed (or chain speed) changes that many times also.

That produces vertical vibration, plus tension vibration
I thought it might be rubbing but it does it on a 25mm road tire too and the frame had clearance for 50+mm tires

sounds like its metal crunching/grinding

there's some rubbing from those rubber spike things on new tires on the inside of the front fork
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Old 02-08-15, 10:16 PM
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Originally Posted by Alias530 View Post
I thought it might be rubbing but it does it on a 25mm road tire too and the frame had clearance for 50+mm tires

sounds like its metal crunching/grinding

there's some rubbing from those rubber spike things on new tires on the inside of the front fork
I wasn't thinking of rubbing within the bike, but against the yoke that supports the trainer's roller. The axle supports aren't super rigid, so when working hard the bike can rock, moving the tire along the roller. Flex hard enough and the tire moves beyond the end of the roller and rubs the supporting yoke.
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Old 02-08-15, 10:43 PM
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Originally Posted by FBinNY View Post
I wasn't thinking of rubbing within the bike, but against the yoke that supports the trainer's roller. The axle supports aren't super rigid, so when working hard the bike can rock, moving the tire along the roller. Flex hard enough and the tire moves beyond the end of the roller and rubs the supporting yoke.
Oh whoops sorry if I wasn't clear... I have two wheelsets. I noticed it on the road a few days ago and on the trainer earlier with the other wheelset/cassette
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Old 02-08-15, 10:50 PM
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Does it make this noise riding on the road, or only on the trainer?
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Old 02-08-15, 11:17 PM
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I never know how much the OP knows or has done prior to posting, so forgive the following question.

You describe "metal crunching/grinding" when using the outer 1/3rd of the cassette. Any chance we're talking about simple chain/front derailleur cage rub?

Otherwise, consider chain plate rub on the chain ring teeth, with lack of lube, or maybe a bit of grit. Simple test here, add some oil to your chain and see if the nature of the sound changes.
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Old 02-09-15, 08:04 AM
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Originally Posted by SalsaShark View Post
Does it make this noise riding on the road, or only on the trainer?
Both. That statement just meant I've tried two different wheels and cassettes and the same problem is there
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Old 02-09-15, 08:05 AM
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Originally Posted by FBinNY View Post
I never know how much the OP knows or has done prior to posting, so forgive the following question.

You describe "metal crunching/grinding" when using the outer 1/3rd of the cassette. Any chance we're talking about simple chain/front derailleur cage rub?

Otherwise, consider chain plate rub on the chain ring teeth, with lack of lube, or maybe a bit of grit. Simple test here, add some oil to your chain and see if the nature of the sound changes.
i guess it could be rubbing the front derailleur. I'll have my fiancée record a video next time I'm on the trainer.

is it nothing to worry about it that's the case?
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Old 02-09-15, 09:03 AM
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Originally Posted by Alias530 View Post
i guess it could be rubbing the front derailleur. I'll have my fiancée record a video next time I'm on the trainer.

is it nothing to worry about it that's the case?
I was wondering if this was it as well. It is just a matter of adjusting your limit screws.

Put your bike in the biggest gear combo you have, big up front small in back, then take a flashlight and hold it under the chain at the front derailleur and backpedal the bike. The light will help you see if it is rubbing at all. Video shouldn’t be necessary.


Skip to 1:20

Last edited by EnsitMike; 02-09-15 at 09:11 AM.
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Old 02-09-15, 10:16 PM
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Originally Posted by EnsitMike View Post
I was wondering if this was it as well. It is just a matter of adjusting your limit screws.

Put your bike in the biggest gear combo you have, big up front small in back, then take a flashlight and hold it under the chain at the front derailleur and backpedal the bike. The light will help you see if it is rubbing at all. Video shouldn’t be necessary.


Skip to 1:20
Thanks for the video... it only happens when standing and mashing though. And it happens in my 8th-11th cogs. In the 8th cog, it's far enough away I wouldn't think derailleur limit would matter??
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Old 02-09-15, 10:55 PM
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Read this thread. Sounds like you have the same problem, and the diagnosis and possible resolution would be the same.
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Old 02-10-15, 07:51 PM
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Sound like a problem I experienced recently. Turns out when I was installing my BB (octalink) the splines were not completely engaged so when I would put a large amount of pressure on the crank I would hear and feel a click/crunch. Check your BB.
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