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Old 01-17-06, 01:58 PM   #1
soda
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1: I did a search
2: the pics in the old threads were deleted
3: I want to make sure that I have the same problem

I noticed my rear rim was cracked around many of the nipples while I was doing some maintenance. Luckily I had a rear rim to replace it with but now I'm curious about the cause for the cracks. Here are some pics. I apologize for the blurry pics but it's a camera phone without focus for closeups.

Any reason for the cracks? Am I doing something wrong or is it just normal wear?

edit: added the bold
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Old 01-17-06, 02:07 PM   #2
TallRider
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Well, your photos aren't focused on the rim well at all, but it looks like the rim is cracking at the spoke nipple. This is one of the ways that rims fail. It could just be age, but rims crack because of stress, which could be caused by your spoke tension being too high. When this happens, it almost always happens to the rear wheel, to the spokes on the drive side of the wheel (the right side, that has the gears). This is because the rear wheel is "dished" to make room for the spokes, so the drive-side spokes are running with less angle (more straight up-and-down) and thus higher tension.
If spokes on the rear wheel are too loose, you risk the non-drive-side spokes failing at the hub because of flexing too much. So there's a balanced happy medium here.

Then again, these cracks are a normal way that a rim fails (and it's gotta eventually wear out somehow). It could be too much riding over bumps and potholes, combined with relatively high spoke tension.
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Old 01-17-06, 04:48 PM   #3
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Quote:
Originally Posted by timcupery
Then again, these cracks are a normal way that a rim fails (and it's gotta eventually wear out somehow). It could be too much riding over bumps and potholes, combined with relatively high spoke tension.
I agree, but I'll add that this only happens on low-quality rims, or any rim with too high spoke tension. It doesn't have to be "normal", and you don't have to tolerate it. Higher-quality rims have a way of reinforcing the holes, such as eyelets or just a thicker wall section. On these you'll wear out the brake track long before they start cracking around the holes.
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Old 01-17-06, 05:44 PM   #4
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Could be plain ol' metal fatigue. Could be overtensioned spokes. Could be poor drilling or finish work. A rough hole is more likely to start a crack than a smooth one.
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Old 01-17-06, 06:55 PM   #5
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My rims have tiny brass rings separating the nipple from the rim. These washer type things are meant to significantly reduce the risk of cracking.

I've got Sun Venus rims.
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Old 01-17-06, 07:59 PM   #6
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First, all rims eventually wear out or fail somehow. Ideally it happens once the sidewall wears through from the brake pads, preferably after 30,000 miles of riding. Secondly, higher-quality rims can have this problem - but as juicemouse says, probably due to overly-high spoke tension. Mavic MA3's have a slight reputation for failing too often at the spoke holes. MA3 had single eyelets (like the "brass rings" that thekid14 mentioned). I had a wheel built with Mavic MA40 (double-eyelet box rim, good reputation for durability) crack at the eyelet on me last summer - only 8,000 miles on the wheel. Rear rim, drive-side eyelet, of course. Perhaps the tension was too high, but I'm not sure.

Anyway, to the original poster: you're probably not doing anything wrong. Unless you built the wheel yourself with really high spoke tension, and/or road on crummy roads with narrow high-pressure tires a lot, etc.
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Old 01-19-06, 10:24 AM   #7
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Thanks for the information about the rim. I didn't build it myself and I have no way of knowing if the spokes were overtightened. Since I trust my shop, my guess is that it's just old.

Thanks for the information though. I always learn something when I come into this forum and you guys did a good job.
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