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Old 10-03-07, 07:21 PM   #1
Rumblejohn
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Too little tension?

I broke a spoke on the rear of my Raliegh hybrid at about 800 miles. I don't know what caused it. I didn't hit anything, or run in a pot hole, but I am a solid 300lbs. The LBS replaced the spoke, and did a really bad job of truing(way over 1/2" lateral) it wasn't much better than when the spoke was broken. I straightened the wheel by loosening the high spots 1/4 turn, and tightening the low spots, to get it passably straight without changing the overall tension much. My question is: the rear wheel seems to have considerably less spoke tension than the front wheel. Could this be why the spoke failed in the first place?

All opinions are greatly appreciated,

John
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Old 10-03-07, 07:37 PM   #2
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With geared bikes the rear driveside (right) spokes normally have the highest tension on the bike and the rear non-driveside spokes have the lowest tension. The front wheel spokes should be equal on both sides with tension a bit less that the driveside rear. The tension differential on the rear wheel is due to the asymetrical hub flanges to make room for the cassette or freewheel cogs. With conventional 8, 9, or 10-speed wheels the non-driveside spokes will have about 65% as much tension as the driveside spokes. This is necessary to center the rim.
Loose spokes break due to excessive flexure, usually in the "J" bend at the hub.

Al
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Old 10-03-07, 07:50 PM   #3
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Loose spokes break due to excessive flexure, usually in the "J" bend at the hub.

That is what I suspected, that is where the break was.

Thanks for the quick reply
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Old 10-03-07, 09:08 PM   #4
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Quote:
Originally Posted by Rumblejohn View Post
Could this be why the spoke failed in the first place?
Yes, yes, and yes. This is the usual failure mode. I'm hard on stuff but I've never had a wheel stay true with less than 500-600 Newtons on the non-drive side.

You're LBS wheel man definitely sounds a little less than competent. Even when I'm being lazy I get things to within 0.05" laterally.

Find someplace with a tensiometer. Assuming it's a basic 32-spoke wheel, get the wheel dished right and true with the drive side at 1200 Newtons. That will leave the non-drive side at 700-800 Newtons.

Bri
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Old 10-04-07, 12:02 AM   #5
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Yes, yes, and yes. This is the usual failure mode. I'm hard on stuff but I've never had a wheel stay true with less than 500-600 Newtons on the non-drive side.

You're LBS wheel man definitely sounds a little less than competent. Even when I'm being lazy I get things to within 0.05" laterally.

Find someplace with a tensiometer. Assuming it's a basic 32-spoke wheel, get the wheel dished right and true with the drive side at 1200 Newtons. That will leave the non-drive side at 700-800 Newtons.

Bri
Broken spoke normally means the wheel is toast, unless something ran into your wheel. It's not a lazy wheel true, it's him not telling you what's wrong with it.

Get it fixed, but after the 3rd broken spoke, lay the wheel to rest. At 300 pounds, I would suggest a 36h rim.
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Old 10-04-07, 12:10 AM   #6
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That sounds familiar, unfortunately the rim is probably shot.
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