Cracks in Spinergy tandem rim
03-22-19, 02:21 PM
#1
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Cracks in Spinergy tandem rim
I happened to notice some hairline fracture lines emanating from several spoke holes on our rear Spinergy Z-lite tandem rim the other day. Not sure how long they have been there, the wheel still was perfectly round and true. The wheels are just over 2 years old with a bit less than 4,000 miles of use. We are a 128 year-old team weighing about 310 lbs riding in hilly terrain. The wheel has an Arai drum plus rim brakes, 9 speed cassette, symmetrically laced with 2-crossed round spokes (no dish). I have been lately running a 32 mm Continental 4-seasons tire on it at 90 psi. The braking surface has not worn down to the thickness indicator and still looks good.
The good news is that Spinergy was great about immediately sending me a new rim with no hassle. They would have replaced the rim had I sent it to them also, but I preferred to do the job myself.
I wondered if the cracks were due to too much spoke tension, but if anything the average tension was a bit low at less than 80 kgf whereas Spinergy recommends greater than 100 kgf. After removing the tire I could also see cracks around the valve stem and access holes which are not subjected to spoke tension. So perhaps the tension was too low allowing the rim to flex excessively? Or maybe it was a bad alloy or extrusion? I would expect many more miles and years normally.
If if you are running Spinergy tandem wheels I would advise you to closely inspect the rim surface for cracks near the spoke holes periodically.
The good news is that Spinergy was great about immediately sending me a new rim with no hassle. They would have replaced the rim had I sent it to them also, but I preferred to do the job myself.
I wondered if the cracks were due to too much spoke tension, but if anything the average tension was a bit low at less than 80 kgf whereas Spinergy recommends greater than 100 kgf. After removing the tire I could also see cracks around the valve stem and access holes which are not subjected to spoke tension. So perhaps the tension was too low allowing the rim to flex excessively? Or maybe it was a bad alloy or extrusion? I would expect many more miles and years normally.
If if you are running Spinergy tandem wheels I would advise you to closely inspect the rim surface for cracks near the spoke holes periodically.
03-22-19, 02:55 PM
#2
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I would not expect that there would be any stress concentration on those inner holes, so those cracks are puzzling. The cracks radiating from the spoke nipple in the last picture is not an uncommon failure for an alloy rim with the stresses of weight and distance. I routinely check our wheels for the later but will have to inspect the innards next time I change tires.
I would be interested if Spinergy has any explanation.
I would be interested if Spinergy has any explanation.
Last edited by Alcanbrad; 03-22-19 at 03:16 PM.
03-24-19, 12:39 PM
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Are these a 24-spoke rim?
Brent
Brent
03-24-19, 01:50 PM
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I would not expect that there would be any stress concentration on those inner holes, so those cracks are puzzling. The cracks radiating from the spoke nipple in the last picture is not an uncommon failure for an alloy rim with the stresses of weight and distance. I routinely check our wheels for the later but will have to inspect the innards next time I change tires.
I would be interested if Spinergy has any explanation.
I would be interested if Spinergy has any explanation.
The only explanation that I can think of for those outer cracks would be repeated lateral flex of the wheel. Out of true? Standing and leaning?
That is, of course, assuming they are actual cracks in the metal.
03-24-19, 02:22 PM
#5
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24 spoke rims. The wheel has been true and trouble free since new. Tough to come up with hypotheses for cracks on the inner holes. Maybe like the unground weld portals on the new San Francisco transit center’s cracked beams, perhaps the drilling left microscopic stress riser points that initiated cracks after repeated rim flex cycles? Dunno, I’m grasping at straws, but I did send a note and picture back to Spinergy.
04-15-19, 05:57 AM
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24 spoke rims. The wheel has been true and trouble free since new. Tough to come up with hypotheses for cracks on the inner holes. Maybe like the unground weld portals on the new San Francisco transit center’s cracked beams, perhaps the drilling left microscopic stress riser points that initiated cracks after repeated rim flex cycles? Dunno, I’m grasping at straws, but I did send a note and picture back to Spinergy.
Two years is soon. I also think the radial lacing may be an issue, or increase the likelihood at least.
04-15-19, 08:15 AM
#7
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The 24 spokes on 28-inch rims don’t go of my mind. With the 310 lbs. team (congrats, a very fit team), probably 40 lbs. for the bike and another 50 lbs. for the gear on overnight tours everything could easily sum up to 400 lbs. On hilly terrain, surely not always asphalt under the tires…
Even with a well-made wheel, taking the rims given I personally would be afraid of putting some overload to the system. Assuming the front wheel has been made under the same conditions: The problems have been occurred to the rear wheel. My feeling is, that this wheel is probably exceeding a limit being not able taking the resulting loads on the long run.
Great move, that Spinergy helped with the replacement with no hassle. Nothing wrong with building a new wheel with those rims either. However, I would have a close look on them and probably rethink the whole (wheel-) setup in the future…
Even with a well-made wheel, taking the rims given I personally would be afraid of putting some overload to the system. Assuming the front wheel has been made under the same conditions: The problems have been occurred to the rear wheel. My feeling is, that this wheel is probably exceeding a limit being not able taking the resulting loads on the long run.
Great move, that Spinergy helped with the replacement with no hassle. Nothing wrong with building a new wheel with those rims either. However, I would have a close look on them and probably rethink the whole (wheel-) setup in the future…
04-15-19, 11:27 AM
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If they are factory built wheels and you are the original owner you may have some recourse, but best to take
them to the LBS that sold them for best access to the manufacturer. The Rolf rear on our Macchiato had similar
cracks at about 1yr after bike purchase and it was replaced by Rolf despite the 1 yr warranty. A friend had a
rear wheel drive hub ratchet tooth break off (pawls and free hub were ok) on a Zipp >3yrs old and it was replaced
under warranty.
them to the LBS that sold them for best access to the manufacturer. The Rolf rear on our Macchiato had similar
cracks at about 1yr after bike purchase and it was replaced by Rolf despite the 1 yr warranty. A friend had a
rear wheel drive hub ratchet tooth break off (pawls and free hub were ok) on a Zipp >3yrs old and it was replaced
under warranty.
Last edited by sch; 04-15-19 at 11:33 AM.
04-15-19, 05:20 PM
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I should reiterate that Spinergy exceeded my expectations by replacing my rim gratis a year after the warranty expired. They immediately sent me a new rim at my request as I felt like that would be simpler and quicker than sending the wheel to them for repair. Replacing the rim was painless. I zip tied the new rim next to the old one and moved the spokes over in the truing stand. It trued up perfectly with the two sides within 3% for tension, and all individual spokes within less than 10% of average. So the rim started out very round and true before mounting.
I tensioned the spokes to around 100 kgf. Spinergy recommends closer to 120, although the wheels were at more like 80 before I started messing with them and I don’t think they changed from the factory as they always ran pretty true. Spinergy cautions against over tensioning because the spokes are more flexible than steel and will over-tension the rim if done by feel. Clearly, too much tension could cause cracks around the spoke holes, but I suppose that having spoke tension too low could allow the rim to flex too much, also resulting in fractures...?
Given our team weight plus bike plus cargo, and our weight distribution, the rear wheel static load could easily be 100 kg. We do frequently climb short grades upwards of 15%, either sitting in a really low gear (26/34) or sometimes out of the saddle in a gear as low as 39/34 for short bursts. Those are probably the times that the rear spokes see the greatest tension, other than hitting potholes at downhill speeds. We also get on unpaved surfaces occasionally, but rarely. Our hub drum brake puts less strain on the wheel than a disc.
You see a lot of these wheels at tandem gatherings. They are comfortable and light. I plan to keep an eye on the rim and monitor tension occasionally, and hopefully get more miles and years from the wheels.
I tensioned the spokes to around 100 kgf. Spinergy recommends closer to 120, although the wheels were at more like 80 before I started messing with them and I don’t think they changed from the factory as they always ran pretty true. Spinergy cautions against over tensioning because the spokes are more flexible than steel and will over-tension the rim if done by feel. Clearly, too much tension could cause cracks around the spoke holes, but I suppose that having spoke tension too low could allow the rim to flex too much, also resulting in fractures...?
Given our team weight plus bike plus cargo, and our weight distribution, the rear wheel static load could easily be 100 kg. We do frequently climb short grades upwards of 15%, either sitting in a really low gear (26/34) or sometimes out of the saddle in a gear as low as 39/34 for short bursts. Those are probably the times that the rear spokes see the greatest tension, other than hitting potholes at downhill speeds. We also get on unpaved surfaces occasionally, but rarely. Our hub drum brake puts less strain on the wheel than a disc.
You see a lot of these wheels at tandem gatherings. They are comfortable and light. I plan to keep an eye on the rim and monitor tension occasionally, and hopefully get more miles and years from the wheels.
04-16-19, 09:46 PM
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I should reiterate that Spinergy exceeded my expectations by replacing my rim gratis a year after the warranty expired. They immediately sent me a new rim at my request as I felt like that would be simpler and quicker than sending the wheel to them for repair. Replacing the rim was painless. I zip tied the new rim next to the old one and moved the spokes over in the truing stand. It trued up perfectly with the two sides within 3% for tension, and all individual spokes within less than 10% of average. So the rim started out very round and true before mounting.
I tensioned the spokes to around 100 kgf. Spinergy recommends closer to 120, although the wheels were at more like 80 before I started messing with them and I don’t think they changed from the factory as they always ran pretty true. Spinergy cautions against over tensioning because the spokes are more flexible than steel and will over-tension the rim if done by feel. Clearly, too much tension could cause cracks around the spoke holes, but I suppose that having spoke tension too low could allow the rim to flex too much, also resulting in fractures...?
Given our team weight plus bike plus cargo, and our weight distribution, the rear wheel static load could easily be 100 kg. We do frequently climb short grades upwards of 15%, either sitting in a really low gear (26/34) or sometimes out of the saddle in a gear as low as 39/34 for short bursts. Those are probably the times that the rear spokes see the greatest tension, other than hitting potholes at downhill speeds. We also get on unpaved surfaces occasionally, but rarely. Our hub drum brake puts less strain on the wheel than a disc.
You see a lot of these wheels at tandem gatherings. They are comfortable and light. I plan to keep an eye on the rim and monitor tension occasionally, and hopefully get more miles and years from the wheels.
I tensioned the spokes to around 100 kgf. Spinergy recommends closer to 120, although the wheels were at more like 80 before I started messing with them and I don’t think they changed from the factory as they always ran pretty true. Spinergy cautions against over tensioning because the spokes are more flexible than steel and will over-tension the rim if done by feel. Clearly, too much tension could cause cracks around the spoke holes, but I suppose that having spoke tension too low could allow the rim to flex too much, also resulting in fractures...?
Given our team weight plus bike plus cargo, and our weight distribution, the rear wheel static load could easily be 100 kg. We do frequently climb short grades upwards of 15%, either sitting in a really low gear (26/34) or sometimes out of the saddle in a gear as low as 39/34 for short bursts. Those are probably the times that the rear spokes see the greatest tension, other than hitting potholes at downhill speeds. We also get on unpaved surfaces occasionally, but rarely. Our hub drum brake puts less strain on the wheel than a disc.
You see a lot of these wheels at tandem gatherings. They are comfortable and light. I plan to keep an eye on the rim and monitor tension occasionally, and hopefully get more miles and years from the wheels.
I'm thinking the low spoke tension is the culprit. We know that spokes fatigue prematurely when they go through a tension / zero tension / tension cycle as the wheel rotates. The heavier the load, the easier this issue will rear its head. A tandem is the perfect example of much higher load on a single wheel, causing sub-optimal tension spokes to fall to zero tension while riding. Since the rim maker specifies a 120 kgf spoke tension maximum, I don't know why you wouldn't want to approach or reach that maximum. Especially on the rear wheel (assuming it's dished - but I think you mentioned it's dishless).
Well, if spokes fatigue prematurely going through this cycle, it seems to me that a rim bed should suffer the same consequence. After all, it's metal going through a fatigue lifecycle as well. But what supports this argument even more is that the rim is ALUMINUM. And we know that 6000 and 7000 series aluminum alloys have a much shorter fatigue lifespan than stainless steel. So I think the culprit is the exact OPPOSITE of overloading (due to a "heavy" team, climbing out of the saddle, or carrying loads), but "underloading" of the low tension spokes and associated spoke hole bed in the rim as the wheel rotates.
I've had several rims crack at the spoke holes over the years, but I just assumed I outlived the rim's useful life. But in thinking back, I seem to recall these failures occurring on the rear wheel NDS spoke holes - exactly where you'd expect zero-tension issues to occur.
I think that was the cause of your rim failure.
And to be clear, what spokes are you using? I realize the photo you show does indicate a non-standard nipple and a larger spoke diameter. I just assumed it was the close-up photo skewing the viewer's perspective. I ask because I'm curious how you're determining your actual spoke tension. Your spoke tension meter will provide spoke tensions for a certain spoke material, usually 1.5mm to 2.0mm stainless steel. If you change gauge or material, you have to determine what tension a measured deflection means. In other words, you have to calibrate your meter for each spoke you use. For example, a butted 2.0/1.8 stainless spoke will have wildly different deflections than a straight gauge aluminum spoke.
I use a decent Ice Toolz tension meter. However, it comes with a rudimentary deflection chart for only three spoke gauges. This quickly became an issue as I built and serviced wheels with many more spoke options. Rebuilding a Ksyrium meant I needed to solve this problem. I eventually purchased a strain gauge and made a jig so I could measure deflections at tensions of 80, 90, 100, 110, 120 and 130 kgf. (I copied a YouTube guy's design, but used wood.) This completely resolved any questions I had about what actual tensions I was achieving during wheelbuilding. I hope you've considered this when measuring and determining spoke tensions in your wheels.
Good luck!
04-16-19, 11:27 PM
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Spinergy wheels use a proprietary polymer composite spoke material:
https://www.spinergy.com/content/pbo-spoke-technology
The company specifies tension in values generated using a Park TM-1 gage, which I have. https://www.spinergy.com/content/bicycle/maintenance
The TM-1 conversion table includes 2.6 mm round Spinergy spokes like mine. I used the table to come up with the 120 kgf number. The actual recommendation from Spinergy is for a TM-1 reading of 22-24 for the drive side. Of course my NDS number should be the same since my wheel is not dished and is laced symmetrically. I left it at the low side of this, 21 on the TM-1, because I have heard that spoke hole cracks can come from too much tension, and also because I believe the wheels were tensioned lower as they came from the factory, maybe because the wheel isn’t dished. For instance, the recommendation for the radial front spokes is 20-23. But you might be right that the root cause could be low tension rather than high. High tension certainly didn’t cause cracks around the hole for the presta valve, for example.
https://www.spinergy.com/content/pbo-spoke-technology
The company specifies tension in values generated using a Park TM-1 gage, which I have. https://www.spinergy.com/content/bicycle/maintenance
The TM-1 conversion table includes 2.6 mm round Spinergy spokes like mine. I used the table to come up with the 120 kgf number. The actual recommendation from Spinergy is for a TM-1 reading of 22-24 for the drive side. Of course my NDS number should be the same since my wheel is not dished and is laced symmetrically. I left it at the low side of this, 21 on the TM-1, because I have heard that spoke hole cracks can come from too much tension, and also because I believe the wheels were tensioned lower as they came from the factory, maybe because the wheel isn’t dished. For instance, the recommendation for the radial front spokes is 20-23. But you might be right that the root cause could be low tension rather than high. High tension certainly didn’t cause cracks around the hole for the presta valve, for example.
