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Rim has begun to split at the seams; how soon will it split completely?

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Rim has begun to split at the seams; how soon will it split completely?

Old 09-16-14, 07:26 PM
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Rim has begun to split at the seams; how soon will it split completely?

My rear tube blew out. The rim's seam has begun to split, the edges
first; an edge cut the side of the tube.

I pinched the edges together with a vise-grip, added a layer of old
tube between the rim and the tube.

I'll get a new rim and build a new wheel as quickly as I can, but that
will take a few days. Can I get any miles out of this jury-rig or
will the rim split completely immediately, with catastrophic
consequences? I don't want to be riding my bicycle when the rim of
the rear wheel comes apart.
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Old 09-16-14, 07:48 PM
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Not nearly enough info for an opinion. What do you mean by splitting at the seam? Normally compression should keep the rim closed at the joint, so is one side shifting sideways, or do you mean that one of the flanges is spreading on one side of the seam? Is there any cracking? how old is the rim, and how worn the brake track? What width tire and pressure?
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Old 09-16-14, 08:09 PM
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Originally Posted by FBinNY
What do you mean by splitting at the seam?
The ends of the vertical part of the rim (are these the flanges?) at the seam have come apart on both sides; one end has splayed a tiny bit more than the other, exposing an edge that cut the tube.

Originally Posted by FBinNY
Normally compression should keep the rim closed at the joint,
The compression of the rim?

Originally Posted by FBinNY
Is there any cracking?
No.

Originally Posted by FBinNY
how old is the rim, and how worn the brake track?
4 years, 26K miles. The brake track is not much worn. I look ahead and slow down, minimizing braking. I'm a 'Sunday driver'.

Originally Posted by FBinNY
What width tire and pressure?
700c Sun CR-18 rim, 700x25 tires, 100 psi (Panaracer RibMo tires rated to 115). I inflate every day I ride.

Last edited by RandomTroll; 09-16-14 at 08:45 PM.
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Old 09-16-14, 09:21 PM
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The rim is under compression because all the spokes are pulling it inward, trying to shrink the diameter of the hoop. That's why pinned rims never pull apart in use.

On clinch rims the tire acta as sort of a splint connecting both the flanges on both sides of the joint, so they tend to stay aligned. So given the age of the rim, I suspect that maybe brake track wear has thinned the flanges enough to allow some movement, and there's different enough support that one side is giving way to the outward force exerted by the tire pressure, even though 25mm tires don't stress rims as much as wider tires might.

To my knowledge there's no calibrated measurement of rim deflection related to tire pressure and how much is acceptable, or what would be a warning sign that there's no longer enough strength. If you own a caliper, you might measure rim width in various places including both sides of the joint, both with the tire uninflated, and at full pressure. If you see significant change it's an indicator that the rim is thinning, especially if it varies all over the rim (thinner areas will deflect more). As I said, there's no standard for what's OK and what's the beginning of the end, but you'll have some sense of it, and can see if it gets worse fairly quickly.

BTW- if you don't own a caliper, make a gauge from an old (or your wife's) credit card. (Amex works best for this). Cut a C shaped slot in one side and trim the points so they just clear the rim when the tire is inflated. Then you can compare the gap when the air is let out to see how much narrower it is. You can use the brake caliper in a similar way, but it has to be centered spot on, and don't let toe-in fool you.
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Old 09-16-14, 09:37 PM
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Originally Posted by RandomTroll
. . . 4 years, 26K miles. The brake track is not much worn. . .
Yes, it is.
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Old 09-17-14, 12:07 AM
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Uninflated, the valve side of the rim is 22.1 mm on the outside; the 2 ends of the seam are 22.9 and 22.5; inflated the valve side is 22.3, the 2 ends of the seam are 23.1 and 22.7. The inside of the rim (spoke side) is about 22.1 everywhere. The rim is supposed to be a flat 22.5 new.

Is this a lot of brake wear? The difference at the seam is a bad sign.

I'm going to replace it for sure. I just want to know if I have to walk until I do. (or - shudder - drive)
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Old 09-17-14, 07:02 AM
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So the rim is gone and may fail sometime in the future. In the meantime the brakes will probably pulse owing to the changes in rim width. But rim wear happens a ta glacial pace and a few more days or weeks probably won't mean anything.

If you're nervous pump the tires 10-15psi higher than riding pressure, then bleed back. That way it's most likely to break while pumping, and if it doesn't then you're riding with a 10psi safety margin.
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Old 09-17-14, 04:52 PM
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I thought about this some more and realized I made a mistake. The tube doesn't touch the flanges of the rim - at least it doesn't as long as the tire's bead clinches the rim - and when that stops happening the tube pushes the tire off the rim and explodes.

I found a small hole in the tire where the rim's split seam cut it. It's too small to let the tube expand out of it; enough must have come out to get cut on the rim's split seam to cut it as well - I think. I could inflate the tire to 100 psi without a boot and just see the hole; it was hard to find on the unmounted tire.
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Old 09-17-14, 05:26 PM
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Stop obsessing. It's a rim and you're replacing it anyway.

If you're concerned, wrap a small piece of duct tape over the bead where it'll be at the rim's seam. Mount, inflate and ride. Meanwhile order a new rim and possibly spokes (Let's not start that debate) and plan on rebuilding in a week or two.
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Old 09-24-14, 07:06 AM
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I'll add a comment about measuring rims and claims of dimension. Just as with tires, rims will have a range of actual dimension and weight. Due to die wear and other manufacturing tolerances the weight (and wall thickness or measured dimensions) can vary by as much as 10% when new. This is a frequent statement in the fine print of manufacturers specs. So a claimed width of 22mm could drift a bit either way and still be within manufactures' tolerance.

Then as rim side walls wear this outer dimension gets further changed from a spec list. Andy.
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Old 09-24-14, 02:01 PM
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Uhhh. Don't ride that wheel. It's going to collapse spectacularly. A girl inflated her tire with our shop compressor recently and it blew the entire brake track off the (worn) rim with a very loud bang. You don't want to have that happen when you're riding....
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Old 09-24-14, 02:26 PM
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Originally Posted by Batavus
Uhhh. Don't ride that wheel. It's going to collapse spectacularly. A girl inflated her tire with our shop compressor recently and it blew the entire brake track off the (worn) rim with a very loud bang. You don't want to have that happen when you're riding....
Brake track failure is more common during inflation rather than while riding (though it can happen either way). One way to ensure that you have the safer stationary failure is to over-inflate 20% then bleed back to riding pressure. This "pressure tests" the rim and ensures a 20% safety margin. (If you have any doubt about the rim strength, wear ear and eye protection during the pressure test)

Also, there will usually be some visible cracks and/or very noticeable brake pulsing as the rim begins to give in areas. Pulsing can give false positives because it can also be caused by dirt or oil on the rim causing variations in friction, but is always worth a closer look. When faced with a rim that pulses, I close the brake to bare contact (near zero braking force) and if it still pulses, that's rim width fluctuation and failure is pretty imminent.
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Old 09-24-14, 02:37 PM
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Remaining brake track aluminum thickness is another thing you can measure, if you bother.
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Old 09-24-14, 02:47 PM
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Why take the risk? Rims don't always fail immediately after inflating the tire. I once inflated a modern road tire to specified pressure (about 8 bar) on a newly built up wheel with a NOS Mavic Ma2. I hung the wheel on a rack on the shop ceiling and went on with other jobs. 5 hours later I heard a peculiar crackling and popping sound. As I looked around the shop to see where it was coming from, the tire blew off the Ma2 rim, almost buckling it. I didn't know then that these classic rims don't take modern pressures very well.

Besides, I wouldn't want to be constantly checking if my rim is about to explode during a ride. That would be detrimental to the experiece of riding, at the very least.
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Old 09-24-14, 02:58 PM
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Originally Posted by Batavus
Why take the risk? ....
If you'd read the thread from the beginning, you'd have seen that the OP knows the rim is likely toast, and was only wondering about using it in the short term while he sourced it's replacement.

In any case, While I agree that "if in doubt, throw it out" is a valid approach, there has to be a basis for when to doubt (and when not to). Unless someone is attuned to reading the warning signs, they have no basis to doubt in the first place. How far to take things is a personal decision, but learning the signs to look for is what makes that more than a matter of crossing your fingers and hoping for the best.
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Old 09-24-14, 03:25 PM
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Originally Posted by FBinNY
If you'd read the thread from the beginning, you'd have seen that the OP knows the rim is likely toast, and was only wondering about using it in the short term while he sourced it's replacement.
Using it in the short term IS taking the risk, so yes I did read that.
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Old 09-24-14, 03:39 PM
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Don't ride it.
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Old 09-24-14, 03:44 PM
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Originally Posted by RandomNonsense
. . . how soon will it split completely? . . . Can I get any miles out of this jury-rig or
will the rim split completely immediately. . .
Hire a psychic?
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Old 09-24-14, 10:22 PM
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I rode it 30 miles before replacing it. It doesn't look any worse for those 30 miles. Though I squeezed the seam-part of the rim flat with vise-grips it splayed out immediately upon riding. The rim scraped a few months of life from the rear brake pads.
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Old 09-24-14, 10:23 PM
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Originally Posted by AnkleWork
Hire a psychic?
I don't know any; can you recommend some?
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Old 09-25-14, 07:48 AM
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Originally Posted by RandomTroll
I don't know any; can you recommend some?
From the way some on this forum speak you'd think there are many right here Andy.
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