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Small cracks in rim along spokes, proper course of action

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Small cracks in rim along spokes, proper course of action

Old 01-03-15, 09:35 AM
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ehilge
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Small cracks in rim along spokes, proper course of action

Hey all, so this past summer I started breaking spokes with some regularity, maybe one or two a month. I wasn't riding that much this fall so I put off addressing the issue until now. I decided to rebuild the wheel using thicker spokes as recommended by my LBS, he didn't think the rim needed to be replaced at the time. I intend to do the work myself. I have a fair bit of repair experience but have never built a wheel. After taking all the spokes off I inspected the rim and noticed cracks around the spoke holes. I attached a couple pictures of the worse instances. I counted something like 11 out of 32 holes that had at least a very small crack next to it. I want to believe its all cosmetic and the rim is fine, but I'm assuming the rim needs to be replaced. It would make sense to me that the spoke issues I had over the summer could have been caused by the wheel coming out of true due the cracks.

Now onto my actual question. Is it more likely that the rim was assembled incorrectly and was damaged due to that, or do I need a heftier rim to keep up with my riding style? The rim itself has maybe 3k miles on it, 1500 of those with touring load. A fair amount of my non-touring riding is on occasionally rough gravel roads so the wheel takes a bit of a beating. According to the website, the rims are Alex XD Comp 29er, 32H. Part of me wants to increase the spoke count, but that would involve getting a new hub as well which I was hoping to avoid. So I ask again, what is the proper course of action considering this little discovery and my riding habits?

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Old 01-03-15, 09:44 AM
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Frist that rims is gone.
For loaded touring more spokes would be a good idea for sure.
As far as why could be several reasons but first would be loose spokes or to much tension and some rims are just known for this type of stuff.
If you need or end up going to more spokes it would be cheaper to just buy a wheel unless your looking for a specific setup.
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Old 01-03-15, 10:20 AM
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Vehicle weight? You, the bike and the expected load.
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Old 01-03-15, 11:01 AM
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Originally Posted by davidad View Post
Vehicle weight? You, the bike and the expected load.
I way about 170, I don't know how much the bike itself weighs, typical touring load is probably around 30lbs almost all on the rear.
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Old 01-03-15, 11:05 AM
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Originally Posted by JTGraphics View Post
Frist that rims is gone.
That's what I think too.
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Old 01-03-15, 11:30 AM
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200 lbs is not unreasonable for 32 holes. Shop for a well reviewed replacement rim.
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Old 01-03-15, 12:39 PM
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Agreed that the rim should be replaced. the cracks will only get worse and trueness stability will suffer.

How many spokes makes a touring rim is decided by whether you're touring on your bike. or not Really there is no threshold when one can or can't do one kind of riding or another kind. I've seen riders with skinny rims and 32 holes riding a camping load with 23mm tires and I've seen training racing on 32mm tires and their commuter road bike. So trying to define what's a touring spoke count is pretty futile. Now there is a range of suitability and when one tries the ends of it then has issues... Well I'll not be kind in my thoughts about the rider's choices.

BITD, with rims that were weaker then today's, at least 36 and often 40 or 48 spokes were considered best for loaded touring. Now 32 spokes are considered enough by many. My choice is 36 spokes because of the added stability and ready rim replacements being available. 36 spoke hubs are made by most all better manufactures still.

Rims which can fit 28-35mm tires are also my choice. So an inside width of 20+mm, outside of 24/26mm are also my choice.

Not yet defined is what is "touring" for the OP. Some will call riding their wanabe racing bike on a van supported multi day ride touring. Others will only call it touring when you're caring all the stuff, regardless of motelling it or camping.

So the answers as to what wheel or bike is good for touring has many answers. But, again, if one chooses a extra light weight bike/wheel/tire and they have mechanical or comfort, or handling problems I'll be the one trying to keep my mouth shut. Andy.
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Old 01-03-15, 12:58 PM
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Thicker spokes is, initially contrary to common sense, often a poor cure for spokes breaking. Also initially contrary to common sense, thinner spokes, and sometimes higher tension are more reliable as cures for spokes breaking. But that rim is done. Sometimes you get superficial cracks in anodized rims, but yours look structural.
Strange though that you managed to combine a symptom of low tension - spokes breaking, with a symptom of high tension - rim cracking.
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Old 01-03-15, 01:47 PM
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Toast. Other random thoughts: That was a pretty short life, but there are so many variables involved, and probably a combination of several including a bad build and bad rim. Don't use straight gage spokes, that will make it worse. A DT compettition, 3 cross is about as reliable as they get. 36s is a marginal improvement, at 230# even I don't always use that. You didn't mention what type of bike it is, but I am assuming disk brakes. Consider larger tires and lower pressures in the rough stuff. If you have limited clearance for tires, consider switching to 650b. More metal would not be my first solution, just how it is used and built.
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Old 01-03-15, 01:56 PM
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Of course the rim is toast, but you want to research the cause before going on with the rebuild.

Stress cracking at the spokes is often the result of too much spoke for the rim, meaning spokes are too thick, or too tight or both. However, with all th cracks longitudinal like this I suspect that something more complex is going on.

These seem to be more fatigue related reflecting changes in the radius of curvature of the rim's profile. We usually see this more in the web (tire side cross member) owing to the compressive action of the brakes, but you're wouldn't be the first, though it's very early onset for the problem.

The profile curvature would also flex with radial deflection, but I wouldn't expect that except with lots of load on a poorly supported rim.

My suggestions
1- replace with a rim from a company with a proven track record. Avoid the high end models which tend to use more brittle aluminum alloys
2- build 32h with 14g DB spokes with 2.0/1.8/2.0 on the right, or to address breakage 2.3/1.8/2.0 if you wish - though I doubt it's necessary. Use 2.0/1.6/2.0 for the left rear and front wheel.
3- lace 3x, and bring tensions to 90kgf front, and about 60kgf left rear, letting the right side end up where it will (about 110kgf estimate).
4- properly set the elbows and stress relieve when finished then touch up.

The above will build a set of resilient wheels that will hold up well to reasonable abuse.
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Old 01-03-15, 02:13 PM
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If you rebuild yourself, rims to consider include Sun CR18, Mavic A319 and A719 in order of increasing cost. Probably you can buy a set of wheels built with A319 rims for not much more than what the rims and spokes cost. Looks like the Mavic rims are about the same width as the Alex that you are replacing -- the Sun, a bit narrower.
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Old 01-03-15, 03:28 PM
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The cost of high quality spokes and a rim as well could well exceed the price of a complete wheel. Going to a higher spoke count would add a margin of safety. A 30 pound load on a rack isn't like an extra 30 pounds of body weight. 30 pounds on a rack is directly over the rear wheel and that weight doesn't move. A rider can stand over rough patches and use legs as suspension, a load attached to the rack can't so that 30 extra pounds is much harder on your rear wheel than extra body weight
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Old 01-03-15, 03:41 PM
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Thanks for all the input! I will try to address some of the points that came up.

Originally Posted by Andrew R Stewart View Post
Not yet defined is what is "touring" for the OP.
Touring for me involves mostly highway riding with enough camping gear to get me through a week or two and enough food to last two or three days. I'm more interested in this bike being durable than lightweight.

Originally Posted by dabac View Post
Thicker spokes is, initially contrary to common sense, often a poor cure for spokes breaking. Also initially contrary to common sense, thinner spokes, and sometimes higher tension are more reliable as cures for spokes breaking. But that rim is done. Sometimes you get superficial cracks in anodized rims, but yours look structural.
Strange though that you managed to combine a symptom of low tension - spokes breaking, with a symptom of high tension - rim cracking.
Could you please elaborate on your reasoning or point me towards a good source? I won't dispute that low tension could lead to spoke failure. But why can't tight spokes also cause a similar issue?

Originally Posted by catgita View Post
You didn't mention what type of bike it is, but I am assuming disk brakes. Consider larger tires and lower pressures in the rough stuff
The bike is a Salsa Vaya 3, model year 2012 for what its worth. Yes, it does have discs, probably not helping my problem. I generally run 32mm tires with 70-80psi.
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Old 01-03-15, 04:07 PM
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Cracks at the spoke holes are fatal. My guess is that it is a single wall rim or double wall rim with single wall eyelets. If so, a double wall, double eyelet rim will go a long way toward eliminating the rim cracking problem.
Was this rim on a front wheel or rear? I ask this mostly in regard to your plans for building a new wheel. The rear wheel usually carries a much larger share of the weight and should be designed accordingly. I like FB's spoke and lacing recommendations (post #10 ).
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Old 01-03-15, 04:18 PM
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Rim is toast and my first thought as to cause of the damage is excessive spoke tension or very uneven spoke tension. Dabac mentioned that you have a combination of a sign of low spoke tension (breaking) and high spoke tension (cracking) problems. Either your tension was really uneven, or it is possible that as the rim cracked and gave a little, tension was lost or made uneven resulting in the spoke failure.

For touring, I personally like 36 double butted spokes (2.0-1.8-2.0) in a double wall eyeletted rim (I'm currently using Mavic A719s). I'm significantly heavier than you and do gravel grinding and winter riding as well as light touring on the bike. I kept the tension at about 115kgf on the drive side rear and about 105kgf on the front. The wheels held true and tension through a full summer of pretty rough use with no spoke breakage.
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Old 01-03-15, 04:35 PM
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I think the triangle or arched profile rims may actually be quite a bit stronger than the flat profile rims. But, they are less commonly found with sockets and eyelets. But, that may not be a problem.

If you're building the wheel, also consider nipple washers.

200 lbs should be ok for 32 holes, but since 36 is commonly available, I'd source the 36h components and do it right. The difference in cost is probably worth less than your labor to assemble it all.
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Old 01-03-15, 05:07 PM
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One other thing not mentioned, which may account for the early onset of the cracking, is corrosion.

When aluminum corrodes, especially from things like exposure to salt, it expands. That means holes get smaller.

Rims are anodized to protect them from corrosion before drilling. That means that every rim has 33 (32h + valve) Achilles' Heels where the sides of the holes expose raw metal. As corrosion happens these holes get smaller, and since the eyelet won't give much, it puts tremendous stress into the area surrounding the hole. The nature of the rims design and how it's produced, are such that spreading stresses are more likely to crack the rim hole to hole, than in any other direction.

Better producers spray protection between the eyelet and rim to prevent the problem. If this isn't done, water will wick into any gap there, and carry corrosives in with it, eventually causing this kind of damage.

The reality is that though rims seem to be very simple products, there's quite a bit of subtle know how involved, which is why some brands are plagued with various problems while others aren't.
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Old 01-03-15, 05:54 PM
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Originally Posted by FBinNY View Post
When aluminum corrodes, especially from things like exposure to salt, it expands. That means holes get smaller.

As corrosion happens these holes get smaller, and since the eyelet won't give much, it puts tremendous stress into the area surrounding the hole. The nature of the rims design and how it's produced, are such that spreading stresses are more likely to crack the rim hole to hole, than in any other direction.
Interesting theory, so spokes without eyelets may actually be stronger in this case.

Assuming this is the rear, were most of the cracks on the right or left, or both? If they are predominately on the right, then it is a spoke count, stretch, and tension problem. If they are also on the left (any?), then corrosion may be the issue.

I did notice your rims seem to have cracking paint... for a 2 yr old bike, that seems premature. For curiosity, you might polish through the paint layer to verify the cracks are true aluminum cracks, but I wouldn't spend the time and expense to rebuild any wheel on questionable rims even if the cracks turn out to be superficial (flip right to left?)

As far as direction of the cracks, for rims with arched profiles, they are thickest parallel to the axis of the rim, and tend to crack towards the sides, but it probably all depends on the rim and manufacture.
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Old 01-03-15, 08:10 PM
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OP, did you buy the bike new? If so, what was the warranty terms...?
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Old 01-03-15, 10:27 PM
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Originally Posted by FBinNY View Post
Rims are anodized to protect them from corrosion before drilling. That means that every rim has 33 (32h + valve) Achilles' Heels where the sides of the holes expose raw metal.
I can't speak for anybody else, but Trek's Matrix rims were anodized after drilling.
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Old 01-03-15, 10:34 PM
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Originally Posted by JohnDThompson View Post
I can't speak for anybody else, but Trek's Matrix rims were anodized after drilling.
Yes, I should have qualified the statement with "many". Anodizing after drilling would likely prevent this kind of corrosion related issue. But, not all rims are made this way. Some (but not all) companies also use an anti-corrosion prep before fitting the eyelet.

On non-eyelet rims it's easy enough to eyeball the holes. With eyelets, you have to trust the maker.

But the fact remains that we see more of this kind of failure with some brands, and less with others, proving that there's more to rim quality than weight and good cosmetics.
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Old 01-03-15, 10:39 PM
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Originally Posted by FBinNY View Post
One other thing not mentioned, which may account for the early onset of the cracking, is corrosion.

When aluminum corrodes, especially from things like exposure to salt, it expands. That means holes get smaller.

Rims are anodized to protect them from corrosion before drilling. That means that every rim has 33 (32h + valve) Achilles' Heels where the sides of the holes expose raw metal. As corrosion happens these holes get smaller, and since the eyelet won't give much, it puts tremendous stress into the area surrounding the hole. The nature of the rims design and how it's produced, are such that spreading stresses are more likely to crack the rim hole to hole, than in any other direction.

Better producers spray protection between the eyelet and rim to prevent the problem. If this isn't done, water will wick into any gap there, and carry corrosives in with it, eventually causing this kind of damage.

The reality is that though rims seem to be very simple products, there's quite a bit of subtle know how involved, which is why some brands are plagued with various problems while others aren't.
Not to mention when dissimilar metals are in contact with each other, galvanic corrosion occurs. Brass nipples, steel spokes, and aluminum rims all wear and as the protective coatings are removed things corrode.
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Old 01-04-15, 09:11 AM
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Originally Posted by JohnDThompson View Post
I can't speak for anybody else, but Trek's Matrix rims were anodized after drilling.
Style is the problem.

Anodized vs. Non-anodized Rims by Jobst Brandt
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Old 01-04-15, 09:14 AM
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Originally Posted by ehilge View Post
I way about 170, I don't know how much the bike itself weighs, typical touring load is probably around 30lbs almost all on the rear.
I had a Mavic Open Pro that had those same cracks. I rode it for quite a few thousand miles before I replaced it. Since you have taken it apart you should discard it.

On a loaded touring bike I would always go with 36 double butted spokes. Makes for a reliable wheel.
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Old 01-04-15, 10:03 AM
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Originally Posted by FBinNY View Post
As corrosion happens these holes get smaller, and since the eyelet won't give much, it puts tremendous stress into the area surrounding the hole.
Nope. For a couple of reasons. While the holes can theoretically decrease in diameter as the corrosion salts fill the hole, the salts have little to no strength and are very brittle. Any movement of the rim...and there is always movement of the rim...would break the salts free and move them out of the hole. Aluminum corrosion salts can easily be flaked off by hand.

Additionally, if the salts were strong enough to hold up to any mechanical movement, you'd expect the cracks to form radially outward from the holes in all directions. The cracks would be star cracks not linear cracks in line with the center line of the rim.

Further, the holes for the nipples in the rim aren't that tight. There is a significant amount of room in the holes for the spokes to turn during the building process. You'd need a lot more corrosion to fill the hole than is evident in ehilge's pictures.

A much more likely cause of the cracks is either spokes that are too tight or too loose. Both can cause the same pattern of cracking. Either way the rim is toast.
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