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Old 06-19-09, 11:17 PM   #1
nathbdp
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Bump at tubular rim joint

Hello all...

While braking on my rear wheel I get a thud sound which apparently is coming from the rim joint. When looking at it in a truing stand it's like the wheel goes slightly out of true at that point maybe 2mm. The drive side bumps out while the non drive side goes in. I tried sanding it down but it's still there. I saw some other posts saying that it will even out with use, or use a file to flatten it. But what about the side that goes inward?

Any help appreciated. It is a velocity escape rim.

Thanks
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Old 06-19-09, 11:56 PM   #2
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Start with a coarse sandpaper and sand it down to as close to even as you can. Add a bit of oil if desired. Switch to a fine sandpaper to buff this down further. Finish up with crocus-cloth to polish and add to shiny brilliance - if you care about appearance. I would.
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Old 06-20-09, 01:34 AM   #3
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No way you're gonna sand off 2mm of metal. Take a picture and post it here.

Sounds like the pinning at the joint has failed and spoke-tension has pulled the rim apart. You can file & sand down minor lips, but the amount of displacement you have is beyond repair. You'll need a new rim if yours is off by that much.
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Old 06-20-09, 01:50 AM   #4
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I concur if it's actually that bad - it's toast. But do post a photo or three.

Have you considered building your own wheels? It's got 3 things going for it: 1. You'll control the operation from the start - checking the rims for such damage and rejecting them/accepting them. 2. You'll learn a skill that most say (I just heard it again this week) requires Einstein to figure out (not). 3. Once you're through the scared-phase, it's fun, relaxing, and allows you a sort of Zen meditative head-space.

Also you have a marketable skill. You can make a few $$$ to enjoy the head-space!

I do wonder if the person who built this wheel had checked the rim first. Or did this come about as a result of over-tightening spokes, or an accident, or what the....!

Does anyone else have experiences with the Velocity Escape rim?
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Old 06-20-09, 10:28 AM   #5
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Hey, thanks for the response. It's probably more like 1mm now that I look at it closer.

Here's a video of the problem I took. I bought the wheelset brand new, never ridden.


http://www.youtube.com/watch?v=KZCjG9QGvBk

Is it within bounds?

Last edited by nathbdp; 06-20-09 at 10:46 AM.
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Old 06-20-09, 03:34 PM   #6
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First off, the wheel is horribly out of true. And there's no close-up of the actual seam joint to show the offset and misalignment. Typically you want to true the wheel radially and laterally before mounting the tyres.
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Old 06-20-09, 04:18 PM   #7
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I don't think it's an issue of being out of true. Maybe I'm wrong. It's just at that one spot that the rim bounces out. I tried originally to adjust it with spoke tension but it didn't do anything because it's limited to such a small area of the rim.

Pics of the seam, both sides.







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Old 06-20-09, 04:32 PM   #8
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You bought them new and never ridden? Unless the vendor was under a tent with a trailer attached to a pick-up truck - RETURN THEM! There is no excuse for letting something like that slip past Quality Control.
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Old 06-20-09, 05:54 PM   #9
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I got them from an individual not a vendor. Basically I don't know if this is acceptable amount of bounce for a rim or not since some places say the seam can be imperfect and it goes away with use (or as you said filing the brake surface). I just don't want to risk the seam cracking or something else. If this is acceptable then I won't bother trying to talk to the seller. He basically said it's because the sidewalls are not machined and it can be reduced with filing.
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Old 06-20-09, 06:15 PM   #10
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Ok, the seam is perfectly fine. I'm not sure where you got the 2mm figure from, but it looks like less than 0.1mm (if any) offset between the rim-ends. Here's what I recommend.

1. remove tyre and clean off all glue

2. true wheel radially and laterally to +/- 0.2mm (0.1mm trueness is available from a lot of wheel-vendors)

3. use calipers and measure the rim-width all the way around. Easiest to clamp it around one spot, then slide the caliper around the rim and feel for sticking points.

4. use a file on the high sides of this seam:


It really doesn't look that bad. It appears to be a criss-cross type of misalignment, so you'll have to file the upper 1/2 of one side and the lower 1/2 of the other side. Then file both in unison to get a perfectly flat surface. Then finish off with fine-grit sandpaper moving along the direction of rotation to blend it all together.
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Old 06-20-09, 06:33 PM   #11
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Thanks! I really don't have an ability to true laterally or radially so I'd have to pay someone to do it. How would this fix the problem since I'm pretty sure it's the rim seam at one point and not the tension? Also measuring the rim width would tell me what?

I'm not crazy anal about the specs, as long as I can get it to work with filing I'd be ok.
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Old 06-20-09, 06:55 PM   #12
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Are these wheels new or used? If truing the wheel to within +/- 0.2mm requires vastly varying tensions between adjacent spokes, I'd say that the rim is tweaked. Which may be indicated somewhat by the offset seam. Tubular rims typically have much better matching seams due to the enclosed rim-profile without the protruding sides of clinchers.

Also, having a wheel that much out of true may indicate a sloppy build with incorrect tension. This will result in lowered wheel-durability; the wheel may go even further out of true easily when hitting bumps & potholes on rides. I would consider this to be a bigger problem than the seam.

As for the seam, it's really not that bad. There's no structural problem at all as pinned seams have been around since the beginning of the bicycle. Just that modern welded and machined rims will save you the hassle of filing and sanding the seam (a 3-5 minute procedure max). There's really no other difference (strength of durability) between a welded versus pinned seam.
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Old 06-20-09, 07:00 PM   #13
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Actually, looking at the video a little closer, it appears the rim very well may be tweaked beyond repair. There's a very sharp jump to the side at certain points (is that the seam?), that may not removed by truing and would require dramatic tension-differences in spoke-tension.

Most shops would charge you about $20 to true a wheel, get that done along with their assessment of the wheel's overall condition. I bet the rim's tweaked.
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Old 06-20-09, 07:08 PM   #14
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Quote:
Originally Posted by DannoXYZ View Post
Also, having a wheel that much out of true may indicate a sloppy build with incorrect tension. This will result in lowered wheel-durability; the wheel may go even further out of true easily when hitting bumps & potholes on rides. I would consider this to be a bigger problem than the seam.
+3

This exactly is what I was thinking. I'd find a spoke-tension gauge and see where it's at. Regardless, if I couldn't return it - I'd rebuild from the beginning.

Good Luck!
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Old 06-20-09, 07:54 PM   #15
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Hmm... it seems there's a misunderstanding. The wheel isn't out of true. It's not a question of spoke tension. The wheel is perfectly round and true. The problem is only at one point, the seam, where apparently the two halves of the rim are slightly misaligned (which apparently happens to some rims during the manufacture?). I don't believe spoke tension can change this. I've had wheels out of true 2-3mm that didn't make the "thump" noise when I braked, indicating that it's a misaligned joint, not a tension question.
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