breaking Mac CN424 spokes

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JoO
Posts: 164
Joined: Thu May 04, 2017 7:30 am

by JoO

Sunday I broke a spoke an my rear wheel.
NDS spoke mac CN 424
broken on the elbow
hub: Bitex RAR9
rim: shallow Velocity Quill (25 mm high)
I built the wheels myself and used a park tool spoke tension tool to get the spoke tension even between the DS spokes and the NDS spokes.
DS = 120 KG tension
NDS = whatever I get the get the wheel dished

This is the second time I broke a spoke on the NDS.
I broke one a month month ago.

The wheels get a beating. before the spoke broke I rode up the molenberg (short cobbled climb) in a high gear.
On the other hand: i weigh only 62 kg and use wide open tubular tires with 60 psi.

What could be the reason?
-the quality of the CN mac 424 spokes
-the geometry of the rear hub => too little NDS spoke tension
-just bad luck (I never broke a spoke before in my life)

by Weenie


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pdlpsher1
Posts: 2392
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

If a spoke breaks at the elbow it's due to movement there which causes fatigue. And the movement is caused by too low of a tension on the NDS. The low tension is dynamic and happens when you hit a bump on the road. Since you are very light I suspect 1) the geometry of the hub isn't ideal, 2) too few spokes, 3) too light of a spoke, and 4) the rim lacks the radial stiffness to transfer the load across many spokes. If you wish to keep the same hub and rim my only recommendation is to use a heavier spoke. The most efficient remedy with the least increase in total wheel weight is use more spokes. Hope this helps.

alcatraz
Posts: 2103
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Maybe your nds flange is too far off center for crossed nds lacing.

Let's say if I had to cross the nds side I would lace the pulling spokes heads out so that they get stressed a bit less. (or whatever spoke it was that broke, i'm going to guess it was heads in)

Are you sure the spokes weren't going completely slack? What's your lowest nds tension? That'd also fatigue a spoke quick.

Could also have been a crappy spoke.

I run cn424 on half a dozen wheelsets and haven't broken one spoke. I've broken some nipples with one or two spokes twisted into spirals. Untwist and reused (for fun) they are still fine.

Marin
Posts: 3473
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

24 spokes and radial on the left?

I agree with the reason being fully unloading the spokes, probably the cobbles?

You can use stiffer spokes on the DS to prevent the NDS unloading. I had 424s break on a RAR9, but I'm 15kg heavier. I rebuilt with 494 on the DS for a much stiffer wheel, but I didn't ride the wheels much after that.

dastott
Posts: 178
Joined: Wed Jun 17, 2015 12:35 pm

by dastott

The 494 is a wide spoke, does it fit in the Rar9 hub without drilling the hub holes?

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WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

Marin wrote:
Thu Jul 18, 2019 1:14 pm
24 spokes and radial on the left?

I agree with the reason being fully unloading the spokes, probably the cobbles?

You can use stiffer spokes on the DS to prevent the NDS unloading. I had 424s break on a RAR9, but I'm 15kg heavier. I rebuilt with 494 on the DS for a much stiffer wheel, but I didn't ride the wheels much after that.
That works given higher DS tensions then. Rather (?) lighter stretchier spoke on NDS to prevent.. mostly-- unloading of that tension? But that likely same scenario albeit less frequent complete unloading. I'm thinking of Lasers which lengthen nicely at higher kgf.

Most ALL the 'new' 11's and up give 40's % tension ratio's NDS vs DS.

Flange to elbow gap.. use of spoke washers to set the elbow closer to flange?

I do not ride rears traditional lacing's... all triplets. I do space some rears over .1" to increase NDS tensions... few times more given circumstances of frame etc. Nearly same effect as OC rims.
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

JoO
Posts: 164
Joined: Thu May 04, 2017 7:30 am

by JoO

WinterRider wrote:
Thu Jul 18, 2019 2:27 pm
Marin wrote:
Thu Jul 18, 2019 1:14 pm
24 spokes and radial on the left?

I agree with the reason being fully unloading the spokes, probably the cobbles?

You can use stiffer spokes on the DS to prevent the NDS unloading. I had 424s break on a RAR9, but I'm 15kg heavier. I rebuilt with 494 on the DS for a much stiffer wheel, but I didn't ride the wheels much after that.
That works given higher DS tensions then. Rather (?) lighter stretchier spoke on NDS to prevent.. mostly-- unloading of that tension? But that likely same scenario albeit less frequent complete unloading. I'm thinking of Lasers which lengthen nicely at higher kgf.

Most ALL the 'new' 11's and up give 40's % tension ratio's NDS vs DS.

Flange to elbow gap.. use of spoke washers to set the elbow closer to flange?

I do not ride rears traditional lacing's... all triplets. I do space some rears over .1" to increase NDS tensions... few times more given circumstances of frame etc. Nearly same effect as OC rims.
The wheel is laced 24 spokes 2x DS and NDS.
What does “space some fear over “ mean?

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pdlpsher1
Posts: 2392
Joined: Thu Jul 19, 2012 6:09 pm
Location: CO

by pdlpsher1

3x lacing will definitely help to reduce spoke detension due to brake forces.


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WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

JoO wrote:
Thu Jul 18, 2019 7:17 pm
WinterRider wrote:
Thu Jul 18, 2019 2:27 pm
Marin wrote:
Thu Jul 18, 2019 1:14 pm
24 spokes and radial on the left?

I agree with the reason being fully unloading the spokes, probably the cobbles?

You can use stiffer spokes on the DS to prevent the NDS unloading. I had 424s break on a RAR9, but I'm 15kg heavier. I rebuilt with 494 on the DS for a much stiffer wheel, but I didn't ride the wheels much after that.
That works given higher DS tensions then. Rather (?) lighter stretchier spoke on NDS to prevent.. mostly-- unloading of that tension? But that likely same scenario albeit less frequent complete unloading. I'm thinking of Lasers which lengthen nicely at higher kgf.

Don't think.. 3x is doable 24H.. :beerchug:

Most ALL the 'new' 11's and up give 40's % tension ratio's NDS vs DS.

Flange to elbow gap.. use of spoke washers to set the elbow closer to flange?

I do not ride rears traditional lacing's... all triplets. I do space some rears over .1" to increase NDS tensions... few times more given circumstances of frame etc. Nearly same effect as OC rims.
The wheel is laced 24 spokes 2x DS and NDS.
What does “space some fear over “ mean?
'fear'..assume you meant 'rear'. Dont see a goof on part spelling.. this time. :smartass: But some say I do....

Rather than equal dishing allowing the rim to run center dead center.. you move the rim center over .1 favoring the NDS to gain the 2.5mm's of spacing.. allowing ~around 7-9 added kgf to the NDS. I can see no handling differences on fast descents. Granted it's a cheat.. works I found.

Don't think 3x works 24H... :beerchug:
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

alcatraz
Posts: 2103
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Weaknesses:

1. rim flex (increases spoke fatigue)
2. undersized spokes
3. heads in at nds flange produces stress on the J-bend depending on hub geometry

Could you take a picture please?

I wish someone could comment on the right way to lace 2x on the nds side. Which spokes go heads in and which go out? Maybe the OP has it the opposite way.

The difference is that pulling spokes see tensions above average, and the opposite ones see below average tensions.

Are you breaking heads-in or heads-out spokes? Pulling or non-pulling spokes?

Maybe you forgot to go over/under at the cross points?

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WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

alcatraz wrote:
Fri Jul 19, 2019 1:01 am
Weaknesses:

1. rim flex (increases spoke fatigue)
2. undersized spokes
3. heads in at nds flange produces stress on the J-bend depending on hub geometry

:lol: C'mon man. :up: .1" over means so little chg is angles... I know... I well know though. Gives the anal view of
the scenario something to go after. Guy isn't riding the Tour de Chems I don't think afterall. :thumbup:

Lasers.. are tough and last. Take your pick: breaking them or some minuscule loss of theoretical lateral stiffness... :noidea:

2x NDS.. did the wheel stay laterally true once built? Minor point.. where the spoke heads set.. meaning to tap them into the hub seat to make sure all flush.

Myself.. always do pulling spokes outbound NDS.. yet mine are all triplet w enough gap to allow all 8 per 16/8's to be outbound.

Wheel simply needs to be laced to avoid NDS going slack on road impacts. Lasers NDS radial outbound is one solution.
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

JoO
Posts: 164
Joined: Thu May 04, 2017 7:30 am

by JoO

Pictures of my wheels.
Broken spoke was non pulling elbow out.
Spoke tension was 110 kgf / 51 kgf without tire installed.
(From memory)
Attachments
86FBF255-888F-4B4D-BC1C-B7C1F86CEBE4.jpeg
9C48E7EE-44F1-4817-A271-D5B57DB9EF0E.jpeg

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WinterRider
Posts: 564
Joined: Tue Feb 05, 2013 2:46 pm

by WinterRider

My glasses are AWOL.. looks like pulling NDS are elbows out.

51 kgf sans tire means near slack spokes when inflated. You need to go 130's-140 max DS.. loosen the NDS and then note the DS
kgf then.. add ~15 kgf keep wheel very round...and then move the NDS into dished position.. incrementally.
Litespeed 2000 Appalachian 61 cm
Litespeed 1998 Blue Ridge 61cm

Fitness rider.. 2 yrs from seven decades age.

That is my story and I'm stick'n to it.

Marin
Posts: 3473
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

dastott wrote:
Thu Jul 18, 2019 2:06 pm
The 494 is a wide spoke, does it fit in the Rar9 hub without drilling the hub holes?

My RAR9 are keyholed.

alcatraz
Posts: 2103
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Pulling nds are elbows out/heads in.

I'd get the DS to 120kgf with tire off (this drops when you put a tire on). 50kgf NDS without a tire could easily become too low on one or two spokes. Also it's an alloy rim so your spoke fluctuations are higher.

I'm not sure if lacing pulling spokes elbows in would solve the problem. It's at least something that can be tried if all else fails. Maybe the flanges are too thick or something.

Edit: Sure the numbers for cn424 with that tension meter are accurate? 120kgf cn424 is painful to squeeze with a bare hand. Leaves a red impression on your palm.

by Weenie


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