Broken Spokes - Causes?

[Gregory Carlsen]

I'm looking for some thoughts on how to correct a issue I'm having with my front (drive) wheel on my V20c. NOTE: This is not the stock wheel - that one is working fine.

A little over a month ago a spoke broke on the non drive side of the front wheel while I was moderately accelerating. The spoke broke at the nipple just where the threads start. I replaced the spoke and spent quite a bit of time making sure the spokes were evenly tensioned using a spoke tension gage. Then on Saturday's ride a second spoke broke on the same non-drive side of the wheel. Again with moderate acceleration. This spoke is 90ish degrees from the previously replaced spoke. I'm replacing that spoke but I'm a bit concerned that there is an underlying issue that I need to resolve. I have been kicking around several ideas that might be the issue. I'm also open to other suggestions.

The wheel in question is a HED Ardennes RA Pro disk brake (drive wheel). It is a 24 spoke, double cross, aluminum rim. Rider weight is 205 and bike is pretty much standard weight. The spokes are Sapim Race J-bend double butted 14/15/14.

The rear wheel (non-drive) is also an Ardennes RA Pro disk 24 spoke 2X and I have not experienced any issues with it.

Do any of the ideas below seem like the right course of action.

1) Replace the second broken spoke and see if another breaks and go from there.
2) Replace all of the (12) spokes on the non-drive side of the wheel and see what happens.
3) Change the non drive side to a 3x pattern.
4) The wheel is just not up to the stress I'm putting on it and I need to replace it with a stronger wheel.
5) Something about the wheel seems defective and I should seek to have it replaced under warranty (There is still 4 years on the warranty).
6) Perhaps the spokes should be a bit longer to better engage the nipple. Should the spokes be even or slightly protrude from the outside of the nipple? The two broken spokes end 3 to 4 mm short of the outside of the nipple.
7) Something else?

I appreciate any additional thoughts you may have.

Greg

 

[Jeffers]

Certainly a detailed post and sounds like you've considered all the options.
One thing specific to FWD Cruzbikes with disc brakes is you've got both the highest braking and drive forces on the same wheel.
Both pulling in opposite directions.
That would sway me towards option #5 and going with a stronger wheel from the same vendor.

 

[Randyc3]

Hi,
I'll second the #5 recommendation. Curious what is the nipple material? Aluminum or brass? When I was riding my upright I would break the aluminum ones and my wheelsmith switched me to brass free of charge. Just a thought....... Good luck.

 

[Robert H.]

Hi Greg, I would think this wheel has something that is not quite up to par. If there is still a warranty, you should pursue that first. Although, they might not honor the warranty being that you have done some of the work yourself.
The 24 spokes 2-cross pattern achieves the ideal balance of strength to weight. You might be able to do a 3-cross pattern on the Ardennes for more strength, but I’m not sure.
I don’t believe your problem is your weight or the stresses of the disc brake. The V20c is pretty close to a 50R/50F weight balance when you are on the bike. A DF road bike will be about 60R/40F. Technically the rear wheel (Front in this case) has less weight on it.
For good thread engagement the end of the spokes should be flush with the end of the nipple. I usually aim to have them even with the bottom of the flat. If they stick out beyond the nipple they are too long and therefore could be running out of thread before the spoke tension is correct. If there are threads exposed below the nipple (towards the center of the wheel) the spokes are too short and will not have enough thread engagement resulting in localized stress concentration.
Things to check:
1. Make sure they laced the wheel correctly. The spoke holes on the rim are not drilled perpendicular to the axle; they are drilled at an angle towards one of the flanges.
2. Check for stress indications on the spoke surface. Look for color differences. A lighter color area indicates the spoke has plastically deformed and is getting ready to fail.
3. Make sure there is no twist in the spokes. Hard to tell with round spokes. Stick some painter’s tap on the spoke and watch for movement when tensioning.
4. Make sure the spoke tension is correct and at the high end of the tolerance. I always set the final tension with the tire mounted and up to pressure. This makes a huge difference if you are running narrow tires at high pressures. The goal here is to make sure the spokes stay tensioned when they are in compression. Spokes work in tension, so if the tension is not high enough to compensate for the unloaded condition (Compression), they will tend to loosen. The movement of the loose spoke will then lead to fatigue failures. See number 5 to avoid this condition
5. Make sure the spoke tension of the wheel is balanced. Use the Park Tool Wheel Tension App (https://www.parktool.com/en-us/wta) for a good visual indication. This will eliminate excessive spoke compression or overloading. Spoke balance is much more important than having a wheel running true. Having said that, when the balance is good, the wheel should be true as well. If that is not the case then there is a problem somewhere.
6. Check the rim for run-out. This should be performed with the wheel disassembled.
7. Check the spoke holes for cracks. This should be performed with the wheel disassembled.
If you can’t get HED to warranty the wheel, then you have a few options if you don’t want to stick with the stock wheelset:
1. Have the wheel completely rebuilt by a competent wheel builder with new spokes and brass nipples. Do not reuse.
2. Buy a new wheel or wheelset. If you want durability, go for something with more spokes and 3-cross lacing that has been hand built.
3. If you like to learn new things: Run the stock wheelset and use this wheel to learn how to build wheels. Plenty of good resources on the web. Then build up a wheelset of your choice once you are proficient. Wheel building is not complicated; it just requires attention to detail.

 

[Gregory Carlsen]

Hi,
I'll second the #5 recommendation. Curious what is the nipple material? Aluminum or brass? When I was riding my upright I would break the aluminum ones and my wheelsmith switched me to brass free of charge. Just a thought....... Good luck.

Thanks for the suggestion. The nipples are brass and they seem to be ok. It is actually the spoke itself that has broken inside the nipple right where the threads start. I was not concerned when one spoke broke but now that a second has broken it seems that this is more than just a random event.

 

[Gregory Carlsen]

Hi Greg, I would think this wheel has something that is not quite up to par. If there is still a warranty, you should pursue that first. Although, they might not honor the warranty being that you have done some of the work yourself.
The 24 spokes 2-cross pattern achieves the ideal balance of strength to weight. You might be able to do a 3-cross pattern on the Ardennes for more strength, but I’m not sure.
I don’t believe your problem is your weight or the stresses of the disc brake. The V20c is pretty close to a 50R/50F weight balance when you are on the bike. A DF road bike will be about 60R/40F. Technically the rear wheel (Front in this case) has less weight on it.
For good thread engagement the end of the spokes should be flush with the end of the nipple. I usually aim to have them even with the bottom of the flat. If they stick out beyond the nipple they are too long and therefore could be running out of thread before the spoke tension is correct. If there are threads exposed below the nipple (towards the center of the wheel) the spokes are too short and will not have enough thread engagement resulting in localized stress concentration.
Things to check:
1. Make sure they laced the wheel correctly. The spoke holes on the rim are not drilled perpendicular to the axle; they are drilled at an angle towards one of the flanges.
2. Check for stress indications on the spoke surface. Look for color differences. A lighter color area indicates the spoke has plastically deformed and is getting ready to fail.
3. Make sure there is no twist in the spokes. Hard to tell with round spokes. Stick some painter’s tap on the spoke and watch for movement when tensioning.
4. Make sure the spoke tension is correct and at the high end of the tolerance. I always set the final tension with the tire mounted and up to pressure. This makes a huge difference if you are running narrow tires at high pressures. The goal here is to make sure the spokes stay tensioned when they are in compression. Spokes work in tension, so if the tension is not high enough to compensate for the unloaded condition (Compression), they will tend to loosen. The movement of the loose spoke will then lead to fatigue failures. See number 5 to avoid this condition
5. Make sure the spoke tension of the wheel is balanced. Use the Park Tool Wheel Tension App (https://www.parktool.com/en-us/wta) for a good visual indication. This will eliminate excessive spoke compression or overloading. Spoke balance is much more important than having a wheel running true. Having said that, when the balance is good, the wheel should be true as well. If that is not the case then there is a problem somewhere.
6. Check the rim for run-out. This should be performed with the wheel disassembled.
7. Check the spoke holes for cracks. This should be performed with the wheel disassembled.
If you can’t get HED to warranty the wheel, then you have a few options if you don’t want to stick with the stock wheelset:
1. Have the wheel completely rebuilt by a competent wheel builder with new spokes and brass nipples. Do not reuse.
2. Buy a new wheel or wheelset. If you want durability, go for something with more spokes and 3-cross lacing that has been hand built.
3. If you like to learn new things: Run the stock wheelset and use this wheel to learn how to build wheels. Plenty of good resources on the web. Then build up a wheelset of your choice once you are proficient. Wheel building is not complicated; it just requires attention to detail.

Thanks for the detailed response and the many very helpful thoughts.

I purchased this wheelset so I would have a spare set of through axle wheels (v20c is my first through axle bike). I have asked HED about warranty coverage and am waiting on a response. Whichever way they want to go on it will be ok. If I end up keeping the wheel it seems like a good opportunity for option 3 - learn a new thing.

Thanks
Greg

 

[Boreen bimbler]

Hi. I once bought my DT Swiss spokes 2mm too long as I was going to use their alu nipples so I could make sure I had as much thread as possible in the nipple. I thought it wouldn't be a problem as the nipples were softer than the spokes. But the nipples were crap so I swapped them for proper brass ones. I had the same problem as you. Spokes breaking at the bottom of the thread. Had to change to the correct size spokes and have done over 13,000km on them problem free since. Including 5 or 6 everestings and some rough roads.
Wheels are 20/24h, rim brake, radial front, 2x DS and radial NDS rear with DT swiss RR411 rims. I'm 72kg and have been building my wheels (and others) for over 30 years but havn't the experience of busy professionals.
As you bought your wheels built I'd try and get them replaced.

 

[Gregory Carlsen]

Thanks for a the comments. They have been very helpful.
I'm thinking I'll replace the second broken spoke, carefully tune the wheel up, and give it another try. I'll see what happens and go from there.

Greg

 

[RAR2]

Thanks for a the comments. They have been very helpful.
I'm thinking I'll replace the second broken spoke, carefully tune the wheel up, and give it another try. I'll see what happens and go from there.

Greg

Good choice.