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  1. #1
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    Opinions wanted: problem retensioning Mavic Cosmos

    So I had some time to kill tonight and got around to a project I've been meaning to tackle for a bit now. I have a set of Mavic Cosmos wheels that I bought a few years back and put about 7,000 miles on (lots of miles near the beach and in the winter). They are currently on my wife's bike and the last time I was checking out the bike I noticed that some of the rear non-drive side spokes had very little tension. The wheel was plenty true but I didn't like the idea of letting those loose spokes go untouched.

    I start retensioning tonight and realize that many of the nipples, especially on the drive side, are really difficult to turn (straight pull spokes twisting isn't helping either). I get the tension evened up and proceed to start retruing. That's when one of the drive side nipples decides to disintegrate. Basically, the flats of the nipple broke off but the spoke is still tight as it's still threaded into the remains of the nipple. Thankfully, the nipples have a hex on the backside which will allow me to back the remains of the nipple off easily, as soon as I find an extra 5.5mm deep socket to machine down small enough to fit inside the rim.

    Finally my question, in your personal opinion of maintaining wheels (for those of you who do such things), what would you recommend:

    a. just replace the broken nipple, lube up the others, and go about truing
    b. replace all of the nipples before going any further as I'm likely to encounter similar problems later on if I don't get any lube on the spoke threads (of course I'd be greasing the spoke threads when I install new nipples)

    Option b is a lot more work but I'm leaning towards it simply because I like knowing a job is done right. I have plenty of extra nipples to use too. Dripping lube onto tight nipples isn't likely to really lube the threads all that much and certainly won't get rid of the existing corrosion.

    I also half-heartedly considered respoking with double butted spokes as well although straight pull spokes seem to be a real pain to source, at least online. I'll be calling the LBS tomorrow to check on the cost though I doubt I'll do it.

  2. #2
    Bill
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    I noticed that some of the rear non-drive side spokes had very little tension.
    How much tension on NDS spokes? How much tension on DS spokes? How many gears on the cassette? Is it dished properly? It's normal for the NDS spokes to be much lower tension than the DS. The more gears the the more assymetrical the wheel and the looser the NDS spokes compared to the DS. If the wheel is true and dished properly the NDS spokes are tensioned proportionately correct. The DS spokes should be in the 80-100kgf range but verify rim mfg specification.


    I start retensioning tonight and realize that many of the nipples, especially on the drive side, are really difficult to turn (straight pull spokes twisting isn't helping either). I get the tension evened up and proceed to start retruing. That's when one of the drive side nipples decides to disintegrate.
    The DS nipples will be harder to turn than the NDS spokes because the spoke tension is much higher. Did you lubricate each nipple at the thread and where it passes through the rim? That is an important step before adjusting nipples especially an older wheels. Do the wheels have aluminum or brass nipples? Brass is stronger. Were you using a good quality, proper fitting spoke wrench? Thats super important to prevent spoke damage.

    Finally my question, in your personal opinion of maintaining wheels (for those of you who do such things), what would you recommend:

    a. just replace the broken nipple, lube up the others, and go about truing
    You pretty much have to replace the broken one and you should have at least put a drop of oil on each spoke thread before adjusting them.
    b. replace all of the nipples before going any further (if you want to and since you have the nipples)
    Option b is a lot more work but I'm leaning towards it simply because I like knowing a job is done right. I have plenty of extra nipples to use too. Dripping lube onto tight nipples isn't likely to really lube the threads all that much and certainly won't get rid of the existing corrosion. Dripping light weight oil into each nipple thread area certainly will help. Use light weight or oil thinned with mineral spirits to aid in penetration and let them sit and soak (so to speak) for a while. It will get into the threads due to capilary action if not too thick. Brass nipples and SS spokes shouldn't corrode.

    I also half-heartedly considered respoking with double butted spokes (double butted spokes will result in longer wheel longevity than straight spokes if tensioned properly ) as well although straight pull spokes seem to be a real pain to source (a real big pain with these type of spokes. Pretty much have to buy from hub mfg), at least online. I'll be calling the LBS tomorrow to check on the cost though I doubt I'll do it.
    [SIGPIC][/SIGPIC]
    Eventually you will reach a point when you stop lying about your age and start bragging about it. - Will Rogers

  3. #3
    Senior Member
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    Well I think I figured out my problem. When I woke up this morning I went over the wheel with my tensionmeter again. I'm not sure what I was doing last night or if things somehow changed overnight but my DS tensions were considerably higher than I was shooting for. Seems to explain the broken nipple. I lubricated all of the nipples and got the wheel dished and trued now (aside from the broken nipple whose spoke is a little too tight still but I'll fix that Monday). I needed to back off on my NDS tension to get the dish right. DS is around 105-120 kgf and NDS is 55-65 kgf.

    Lessons learned: lubricate nipples especially on a wheel that's seen lots of bad weather and don't go crazy with tension.

    FWIW, when I started working on this wheel some of the NDS spokes were off the Park Tool conversion chart on the low side. They are straight gauge 2mm spokes and were reading about 14-15 on the tensionmeter.

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