sirious94

Hello,

I have a set of Mavic CXP-22 laced to Cannondale Coda hubs (i believe just from the factory) they are pretty old, but now one of the spokes in the rear non drive side is loosing it's tension. I noticed it, tightened and re-trued it, and now it has no tension again. it's the same spoke because it's two up from the spoke with my wheel magnet.

How do I fix this? Do I need a new spoke? What might be causing it to just lose tension? Thanks.

Al1943

Take a look at the "J" bend in the spoke, found at the hub flange. It may be about to break.
Also look for small cracks in the rim near the spoke holes. This is where rims usually fail. If there are any cracks the rim needs replacing.
It's quite possible that you do not have enough tension in the spokes. Because of the rear wheel's offset hub flanges the non-drive side spokes have the lowest tension and if too low will break at the "J" bend due to excess flexure.

FastJake

+1

If the other spokes are ok, I'd just replace that one. Spokes are pretty cheap if you only have to buy one. It'll be worth it to prevent a failure out on the road. Maybe the threads are stripped?

bikeman715

I agree with FastJake about stripped threads the spoke and/or the nipple . I would replace both.

davidad

I doubt that you would strip the threads on a SS spoke with a brass or aluminum nipple.
Sounds like the drive side tension is not high enough. The left side is usually 50 to 65% of the drive side tension.

bikeman715

the strip threads would be with the nipple not so much with the spoke.

Drew Eckhardt 

The tension in that spoke is too low for friction to keep the nipple from turning when it unloads as it passes the bottom of the wheel.

The wheel could have been trued incorrectly resulting in uneven tension, the rim could have a bend in the direction of that spoke which makes it impossible to have the wheel true with sufficient tension in that spoke, the spoke could be failing, or the nipple could be pulling out of a failing socket.

You start by making sure the spokes have uniform tension on both sides of the wheel. If you can't do that without loosing true you'll need to loosen the spokes and bend the rim back or replace it. Then make sure they have enough tension. Light box section rims with 36 or fewer spokes can be set with Jobst Brandt's method of increasing tension then stress relieving until the rim deforms in waves, backing off half a turn, and re-truing. A tension meter is simplest.

My last front wheel stayed true for over ten years after I built it until I put a bend in it with the spokes around the bend needing to be twice as tight on one side after which it wouldn't stay true for a hundred miles.

FastJake

This is fine for a front wheel, but the OP is having problems with the rear wheel which will have higher tension on one side (unless it's a FG/SS bike.)

Drew Eckhardt 

In hindsight I was clear as mud.

By "uniform tension on both sides of the wheel" I mean that both sides must each have uniform tension among their spokes - all the same on the left, all the same on the right. Obviously they'll only be the same on both sides when the spokes are at the same angle.

Some variation may exist at the rim joint.