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Spoke tension vs rim cracking

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Spoke tension vs rim cracking

Old 02-05-19, 02:34 PM
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Spoke tension vs rim cracking

Greetings all. I built this wheel nearly 20 years ago, and found last week that it could disintegrate at any moment. I found another rim and have swapped them, but not before checking the tension. The tool I have equated to 99-110kgf, with reasonable consistency around the wheel. Looking at this thread that should be about right, so why the cracking? Should I just tension lower (like 90kgf) or stick with what was ordained by the greats?
King hub, F519 rim, DT Supercomp spokes and nipples, replaced in the rebuild.
Cheers
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Old 02-05-19, 03:01 PM
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I'd guess that the spoke tension isn't really to blame. In 20 years, a wheel goes through a lot. Aluminum alloy rims tend to crack at some point, if subjected to enough stress.
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Old 02-05-19, 03:28 PM
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For a symmetrical front wheel, I don't go over 90 kgf. If I wasn't "hefty", I'd go a little less.
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Old 02-05-19, 03:38 PM
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It's a symetrical rear, and I'm about 190/92kg. It's done the Test of metal in Squamish, a couple of team 24hr races and 2 Fruita Fat tyres (tires..) plus quite a lot of other stuff. I suppose I can put it down to wear and tear. 20 odd years older now so I think 90 is what I'll aim at. Thanks for the replies.
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Old 02-05-19, 03:48 PM
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Any chance your tool is out of calibration? I read a thread a year or so about a guy who thought he had built his wheels within spec, but his tensiometer read at least 10kgf low, and that was just enough to crack them after some miles.

I see that these Mavics don't have double-eyelets, so it's all up to those exterior walls to carry the spoke tension.
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Old 02-05-19, 10:58 PM
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My Mavic Open Sport rear rim had two cracks like that after 10 years of riding. I used to weigh around 240 lbs., under 200 now. I thought it might be my weight, but it did hold up for 10 years. I never checked the spoke tension or broke any spokes on the wheel, it just developed cracks one day. Mine weren't as severe and yours, still worrying.

Two spokes had cracks like this.

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Old 02-06-19, 09:44 AM
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See, this is why you need to use rim brakes and ride through mud every so often. Wear the brake track out so the rim needs to be replaced before it cracks from old age.

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Old 02-06-19, 10:07 AM
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It's just fatigue cracking, nothing lasts forever... especially aluminum.
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Old 02-06-19, 11:31 AM
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So this one is done, and at lower kgf than before. My tensioner is a Park tool, with an adjustable screw on the spring. In theory, if I lock the elbow in place and hang a weight on the other end (I weigh just over 90kg!) I could calibrate it!

Discuss...
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Old 02-06-19, 11:32 AM
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Originally Posted by Trevtassie View Post
It's just fatigue cracking, nothing lasts forever... especially aluminum.
Have you read any Nevil Shute?
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Old 02-06-19, 11:34 AM
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Twenty years on light weight rims? The tension must have been as close to perfect as it could have been. Going forward, what unintended consequences will reduced tension bring? And when?
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Old 02-06-19, 11:58 AM
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Originally Posted by AnkleWork View Post
Twenty years on light weight rims? The tension must have been as close to perfect as it could have been. Going forward, what unintended consequences will reduced tension bring? And when?
I'm 20 years older, I don't expect them to get anything remotely like the abuse they had!
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Old 02-07-19, 04:02 AM
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Originally Posted by MiloFrance View Post
Have you read any Nevil Shute?
Read On the Beach but haven't read No Highway.... wonder if it's on Kindle?
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Old 02-07-19, 12:58 PM
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Originally Posted by MiloFrance View Post
I'm 20 years older, I don't expect them to get anything remotely like the abuse they had!
What tire widths and pressures were you using? In principle, these shouldn't affect a good wheel, but we know that a bigger tire at lower pressure passes less stress onto the rim and spokes.
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Old 02-07-19, 01:10 PM
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Hell, I had a wheel develop those cracks after one year/4k miles. WTB rim, 32h/3x. And if anything, the spoke tension always seemed a little low. If you got 20 years out of it, well done!
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Old 02-07-19, 02:23 PM
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More spokes , wheel load is shared , fewer the tension has to support a bigger quadrant of Rim..
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Old 02-07-19, 02:53 PM
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Butted 15-gauge spokes tend to be easier on rims. To DT's credit, back when I still worked in a bike shop in the 1990s, they listed 14-gauge spokes in their catalog as "tandem" spokes. Don't know whether they still list them that way.
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