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Cracked rim .. whos to blame?

Old 08-07-17, 05:09 PM
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epnnf
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Cracked rim .. whos to blame?

...putting on a new rear tire on my 2016 Masi, noticed the rim is cracked on most of the spokes on the chain side. Took it to the LBS where I bought it; they will get back to me, but probably new wheel w/existing cassette, which is in good shape. It has happened once before in my 25 yrs of riding as an adult, that was caused, I think, by riding over those 1" construction plates on the road. NP w/front rim. I weigh bout 175#. btw, this wheel broke a spoke several months ago. I got the bike Feb2016; has bout 6K miles. Tires are 38mm wide; bout 70psi. The spokes seem tight, but rear wheel spokes always seem tight to me. So, my ?s- How/why did this happen? How to prevent it from happening again? When ya buy a new bike, are the wheels shipped assembled, or does the LBS build them? I trust the guy @ my shop.
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Old 08-07-17, 05:15 PM
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What rim ?, how many and what type spokes ?. Factory or hand built ?.

Pictures ?
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Old 08-07-17, 06:45 PM
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Originally Posted by epnnf View Post
...putting on a new rear tire on my 2016 Masi, noticed the rim is cracked on most of the spokes on the chain side. Took it to the LBS where I bought it; they will get back to me, but probably new wheel w/existing cassette, which is in good shape. It has happened once before in my 25 yrs of riding as an adult, that was caused, I think, by riding over those 1" construction plates on the road. NP w/front rim. I weigh bout 175#. btw, this wheel broke a spoke several months ago. I got the bike Feb2016; has bout 6K miles. Tires are 38mm wide; bout 70psi. The spokes seem tight, but rear wheel spokes always seem tight to me. So, my ?s- How/why did this happen? How to prevent it from happening again? When ya buy a new bike, are the wheels shipped assembled, or does the LBS build them? I trust the guy @ my shop.
Too many variables to say one way or the other. Riding over potholes, plates or other things in the road has little to no bearing on wheel longevity. Generally speaking, to damage a rim while riding is going to involve rim dents (called "blips") because the tire squashes far enough for the rim to come in contact with whatever you hit.

But, on the other hand, stuff happens.

On the other hand, you do have enough mileage to damage a wheel that was improperly built or insufficiently tensioned.

On the other hand, spokes that are too tight can cause the same result.

On still another hand, the rim may be defective.

On still another hand (going of the octopus here), the bike is likely out of warranty so you'll just need to buy a new wheel.

As for the bicycle process, yes, the wheels are preassembled as is most of the bike. The mechanic takes the bike out of the box and finishes assembly and makes adjustments. Some of those adjustments may need to be done to the wheel...machines don't do a very good job of tensioning the spokes...but, in my experience, that isn't always done.

Sometimes that matters and sometimes it doesn't. I've seen 30 year old wheels that have spokes that are barely finger tight but have been ridden for those 30 years and other wheels that are nice and tight but fracture after a few thousand miles. It's often hard to tell what is the cause or predict what will fail.

Talk to the LBS and hope that they will do something for you. If they don't, don't get your knickers in a knot and just accept that you might need to get a new wheel. You can still be partly (or mostly) to blame.
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Old 08-07-17, 07:39 PM
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70 psi seems high for someone who only weighs 175 lbs, but that probably doesn't have anything to do with it.

Pictures of the gore, any extra details about the wheels would be great.
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Old 08-07-17, 09:06 PM
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Next time buy wheels with overbuilt(heavier) rims, and a higher number of spokes in them (32 and up).

more spokes means less tension required per spoke, reduced chance of overloading the rim and cracking the spoke holes.
make it a big heavy double-walled box section rim, with double spoke eyelets on it.

Yeah, a wheel that takes up half the weight of your bike doesn't sound appealing to a road racer, but if you insist on ultralight stuff you have to live with the consequences - they break once 'race day' is past.


anyway, in practice, few LBSs and even fewer customers have a good understanding of metallurgy and wheel failure. So in general causality and fault are glossed over in favor of: is it within the warranty period or not?
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Old 08-07-17, 09:36 PM
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Get Velocity Dyad rims, perfect with 35 mm tires, I have 4 now. They have a pointy shape for strength and no STUPID eyelets..... A solution to a problem they caused. LOL
My bikes total is 225 lbs on a light day, 290 on tour. Two with Sturmey Archer 36H hubs, front 22,000 miles and rear 10,500 miles. Rohloff 32H has 11,000 miles. They look like new, NO busted spokes. Only 2 flat tires actually. I also used nylock nipples, that help a lot.

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Old 08-07-17, 09:49 PM
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As noted by others, there are too many unknowns.

For me, a key would be the nature of the cracks themselves. Are they local cracks at each spoke hole, or cracks propagating spoke hole to spoke hole as if the rim was starting to split in half?

Then, knowing which rim (some have been known to crack) the spoke gauge, and whatever info you have about the built. It's too late now, but it would also have been nice to know the tension it was built to.

Lastly, since you're using wider tires, the pressure may be a factor. The "hoop stress" pulling the rim apart side to side (as to split it down the center) is proportional to the pressure X the width. A wide tire at high pressure creates significant tension in the upper (tire side) rim surface. I doubt it could ever be high enough to tear the rim apart, but since the member is curved, the tension combined with the flexing as it rolls can make for some interesting deflections there, and possibly to premature fatigue failure.

So, there's the rim, there's the builder, and there's you, and odds are you each contributed in your own way.
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Old 08-08-17, 07:21 AM
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Too much tension in the spokes can lead to cracking at the spoke holes. This can especially be a problem with single-wall rims lacking eyelets when no nipple washers are used.
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