Cracked cranks? How much of a problem is this?

Tak · 2011-08-06, 01:24 PM

Hello,
After my ride today, I noticed that one of my cranks appears to be cracked. The crack runs across the top of the crank and about halfway across the back, widthwise.
I have the Qu-Ax aluminum cranks.

These things are solid aluminum, aren't they? Is there some kind of finish that could be degrading, or is my crank just going to snap in half one day when I drop off a curb?

tholub · 2011-08-06, 04:06 PM

Given that those are the Qu-Ax cranks, I would expect that the cracks are structural and that you're not far from having them fail. You might want to get a set of stronger cranks on order.

Max_Dingemans · 2011-08-06, 04:19 PM

In my experience cranks usually snap off when starting or stopping rapidly. I'm with Tom though, it's time for a new set of the same at the very least.

brendan · 2011-08-07, 04:45 PM

I've never seen cranks fail like that. So I don't think thats a crack. I might be wrong but I've never seen even a picture of a crack right down the middle of an al crank. Aluminium cranks usually twist.

I've been fairly silly on quax ISIS cranks on a 20" freestyle and they always held up.

Either way, a crank breaking whilst going down a curb wouldn't hurt that much so I would just ride them until they fail. I've had pedals snap off whilst riding and it's not really that bad. If you are doing trials and are a full size adult it might be a good idea to upgrade to something tougher before they twist and become useless though!

tholub · 2011-08-07, 04:55 PM

Quote:

Originally Posted by brendan

I've never seen cranks fail like that. So I don't think thats a crack. I might be wrong but I've never seen even a picture of a crack right down the middle of an al crank. Aluminium cranks usually twist.

I have seen Qu-Ax cranks break clean through right at that point.

brendan · 2011-08-08, 06:12 AM

Quote:

Originally Posted by tholub

I have seen Qu-Ax cranks break clean through right at that point.

I'd love to see a picture if you have one. I'm considering buying a nimbus eclipse and putting qu-ax cranks on like these because they are lighter than the ventures. But if they are just gonna snap...

Tak · 2011-08-07, 06:56 PM

Quote:

Originally Posted by brendan

If you are doing trials and are a full size adult it might be a good idea to upgrade to something tougher before they twist and become useless though!

Not doing trials, but I'm definitely a "full size adult."

I guess this is my excuse to get a pair of 137/165 moments.
Thanks for the feedback!

rob.northcott · 2011-08-08, 11:21 AM

Quote:

Originally Posted by brendan

a crank breaking whilst going down a curb wouldn't hurt that much so I would just ride them until they fail. I've had pedals snap off whilst riding and it's not really that bad.

But you're young and bouncy Brendan

Nurse Ben · 2011-08-08, 12:53 PM

I have run the QuAx lightweight cranks and they worked well until I started getting some slippage at the spline. I run the 170's and weigh 200#, not cracks or failures.

If you want some strong and light cranks, the Venture II are very nice, I have 165's and 150's, nice low Q. The dual hole moments are super heavy, not worth the trouble unless you switch crank length often.

corbin · 2011-08-09, 05:10 AM

Quote:

Originally Posted by brendan

I've never seen cranks fail like that. So I don't think thats a crack. I might be wrong but I've never seen even a picture of a crack right down the middle of an al crank. Aluminium cranks usually twist.
!

Steel cranks usually twist. Aluminum usually snap. It's just the way the metal fatigues.

corbin

brendan · 2011-08-10, 06:53 AM

Quote:

Originally Posted by corbin

Steel cranks usually twist. Aluminum usually snap. It's just the way the metal fatigues.

corbin

I've still never seen aluminium cranks snapped there. Pics?

2011-08-06, 01:24 PM	#1
Tak Respiring Unicyclist Join Date: May 2008 Location: København Posts: 417	Cracked cranks? How much of a problem is this? Hello, After my ride today, I noticed that one of my cranks appears to be cracked. The crack runs across the top of the crank and about halfway across the back, widthwise. I have the Qu-Ax aluminum cranks. These things are solid aluminum, aren't they? Is there some kind of finish that could be degrading, or is my crank just going to snap in half one day when I drop off a curb? Attached Images __________________ http://clevercycles.com/energy_and_equity http://goo.gl/l64bW

2011-08-06, 04:19 PM	#3
Max_Dingemans Pedal Pedal Crash Join Date: Oct 2002 Location: Minneapolis, MN Posts: 1,391	In my experience cranks usually snap off when starting or stopping rapidly. I'm with Tom though, it's time for a new set of the same at the very least. Last edited by Max_Dingemans; 2011-08-06 at 04:25 PM.

2011-08-07, 04:45 PM	#4
brendan Unicycling = trials Join Date: Oct 2006 Location: UK - Cambridge/Canterbury Age: 23 Posts: 2,184	I've never seen cranks fail like that. So I don't think thats a crack. I might be wrong but I've never seen even a picture of a crack right down the middle of an al crank. Aluminium cranks usually twist. I've been fairly silly on quax ISIS cranks on a 20" freestyle and they always held up. Either way, a crank breaking whilst going down a curb wouldn't hurt that much so I would just ride them until they fail. I've had pedals snap off whilst riding and it's not really that bad. If you are doing trials and are a full size adult it might be a good idea to upgrade to something tougher before they twist and become useless though! __________________ I'm a soldja. Last edited by brendan; 2011-08-07 at 04:46 PM.

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2011-08-06, 04:06 PM	#2
tholub Totally Doable Join Date: Apr 2002 Location: Berkeley, CA Age: 44 Posts: 3,244	Given that those are the Qu-Ax cranks, I would expect that the cracks are structural and that you're not far from having them fail. You might want to get a set of stronger cranks on order.

2011-08-08, 12:53 PM	#9
Nurse Ben XC Muni Join Date: Jul 2008 Location: Southeast USA Age: 47 Posts: 3,952	I have run the QuAx lightweight cranks and they worked well until I started getting some slippage at the spline. I run the 170's and weigh 200#, not cracks or failures. If you want some strong and light cranks, the Venture II are very nice, I have 165's and 150's, nice low Q. The dual hole moments are super heavy, not worth the trouble unless you switch crank length often.

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