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  1. #1
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    Pacenti rim cracks

    Just looked over my wheel to check everything and make sure it was all good and found some cracks. Here is the worst one. Notes from when I built the wheel have this one at 15 (131Kgf) on a park meter. Cracks are on the DS. Rim has a couple thousand miles maybe 4kish. These were some of the first rims released and got them from Fairwheelbikes.

    Anyone else have this happen?

    Pacenti rim cracks-imageuploadedbytapatalk1396149075.344722.jpg
    Last edited by jmorgan; 03-29-2014 at 07:27 PM.
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  2. #2
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    I had one rear wheel that I have built with an SL23 rim come back after 6 months with similar cracks on some rear DS spoke holes. I didn't exceed 120kg-f spoke tension. That was a 24 spoke wheel with a 160lb rider.

    I rebuilt it with Sapim small oval nipple washers and hope it will last this time.
    Valley Cyclist Wheels www.valleycyclist.com

  3. #3
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    Quote Originally Posted by valleycyclist View Post
    I had one rear wheel that I have built with an SL23 rim come back after 6 months with similar cracks on some rear DS spoke holes. I didn't exceed 120kg-f spoke tension. That was a 24 spoke wheel with a 160lb rider.

    I rebuilt it with Sapim small oval nipple washers and hope it will last this time.
    This is also 24 hole DS spokes and im 160 now, was maybe 180 when they were first built.

    I notice looking on FWB that in the comments they recommend 110Kgf now. I know when I built it everyone was saying 130 was fine. 110 sounds a bit low bit low especially if I was using a crappy hub (I'm using CK).
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  4. #4
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    Pacenti rim cracks

    Quote Originally Posted by jmorgan View Post
    110 sounds a bit low bit low especially if I was using a crappy hub (I'm using CK).
    I agree. If the hub geometry results to a tension ratio of 0.45 or below, the expected NDS tension will be below 50 kgf and, IMO, it's not enough to reliably keep nipples in check unless you Loctite them although doing so would give you another set of problems.
    Furthermore, if the rim consistently cracks at 120 kgf I would not trust it at 110 kgf simply because I consider such a small reduction in tension logistically very difficult to reliably measure with the commonly available tension meters and their margin of error. I would want to have a greater safety margin, more like around 20 kgf, to allow for variances in tension measurement accuracy. Note that even the highest quality meter is subject to a 10% error.

    Edit to add: 28 and 32 spoke rims may fare better since more spokes carry the load.
    Last edited by dcgriz; 03-30-2014 at 04:23 AM.
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  5. #5
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    I had the same thing happen, 24h rear, 7801 hub, built to ~115 DS tension, 130 pound rider. After about 2000 miles the first cracks appeared. I rebuilt with an XR-279. She didn't like the Kinlin's extra weight, but the rim holds up just fine.

  6. #6
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    I've sent out a few hundred rims and got one back. I take that to my fault because the tension was cranked too high (one of the first wheels out). Since then I've kept the tension at about 125kgf and haven't had any other rims back. I think at that tension all is well.

  7. #7
    Bog
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    One thing I don't understand about ultimate wheel tension and is not often mentioned in these discussions is that when you put a tyre on a rim and pump it up to 100 psi say, the spoke tensions in the wheel drop by about 10 kgf. Surely this will tend to reduce the build tensions down to below rim manufacturers recommended levels.

    If you build a wheel at the lower end of recommended rim tensions because you may be worried about eyelet cracking, then isn't there a danger that the NDS spoke tension could be dangerously low?

  8. #8
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    Pacenti rim cracks

    It appears that accurately determining the applied spoke tension to this rim is paramount because the threshold seems to hover around the 120-125 kgf mark.

    Calibrating the tension meter and particularly a meter like the Park for the exact load and specific spoke in use seems to be critical if the maximum allowable tension is to be applied and long term rim durability is also desired.

    These are the challenges bestowed by the seemingly continuous market push to reduce component weight and our understanding on when and how to best use these components when choosing wheels for racing, training or racing/training.
    With bicycles in particular, you need to separate between what's merely true and what's important.

  9. #9
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    Just a question, because I have a set of Pacentis that still seem OK but I know I built them to a fairly high tension...............

    As well as static tension, is not dynamic tension just as, if not more important, when thinking about this issue? And wouldn't dynamic tension at the rim be also a function of the elasticity of the spoke? So would using a skinny spoke like a Laser be less stressful over the bumps than a straight gauge spoke?

    Just asking.
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  10. #10
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    Pacenti rim cracks

    Quote Originally Posted by Bog View Post
    One thing I don't understand about ultimate wheel tension and is not often mentioned in these discussions is that when you put a tyre on a rim and pump it up to 100 psi say, the spoke tensions in the wheel drop by about 10 kgf. Surely this will tend to reduce the build tensions down to below rim manufacturers recommended levels.

    If you build a wheel at the lower end of recommended rim tensions because you may be worried about eyelet cracking, then isn't there a danger that the NDS spoke tension could be dangerously low?
    The 120 kgf tension limit has been the rim manufacturer's max safe allowable limit for a very long time and before the lightweight rims earned such popularity. DT Swiss, for instance, is listing 120 kgf for all of their rims including the double eyeleted, the 585, the 540, the e-trek and everything else in between. I think it had been derived with a lot of inherited safety, in a similar fashion as the max allowable pressure stamped on the side of the tires, for rims that were constructed for higher tension thresholds.
    Nowadays we are pushing more and more for lesser weight but thinner extrusions with taller rims for harnessing aero benefits are taxing this convention.

    IMO, the user needs to decide and pick the best rim for the application. If the rim is designed to be part of a racing wheel then immediate performance is the primary concern and long term durability should be of secondary importance. Similarly, a do it all combination racing/training wheel should not use a lightweight rim with the lowest number of spokes possible, if long term durability is in focus.
    With bicycles in particular, you need to separate between what's merely true and what's important.

  11. #11
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    Pacenti rim cracks

    Quote Originally Posted by bikerjulio View Post
    Just a question, because I have a set of Pacentis that still seem OK but I know I built them to a fairly high tension...............

    As well as static tension, is not dynamic tension just as, if not more important, when thinking about this issue? And wouldn't dynamic tension at the rim be also a function of the elasticity of the spoke? So would using a skinny spoke like a Laser be less stressful over the bumps than a straight gauge spoke?

    Just asking.
    It seems to me, the number of spokes would play a greater role rather than the type of spokes because the fewer the spokes the higher the load each sees when they go through the loading/unloading cycles when the wheel is in use.
    With bicycles in particular, you need to separate between what's merely true and what's important.

  12. #12
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    Pacenti rim cracks

    I'm about to build up a set of wheels with the SL23 and wasn't sure if I should worry about nipple washers - ended up contacting Pacenti for advice. I received an email from Kirk Pacenti himself advising me to use nipple washers. I expect this will reduce the likelihood of cracking.

    (FYI He also advised me (180 lbs) to go with a 24/28 spoke count instead of the 20/24 I had planned).

  13. #13
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    This thread is making me think of going back and rebuilding my rear wheel with DS washers.
    There's sometimes a buggy.
    How many drivers does a buggy have?

    One.

    So let's just say I'm drivin' this buggy...
    and if you fix your attitude you can ride along with me.

    http://www.youtube.com/watch?v=GekiIMh4ZkM

  14. #14
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    Quote Originally Posted by bikerjulio View Post
    This thread is making me think of going back and rebuilding my rear wheel with DS washers.
    Maybe that's not a bad idea.
    .
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  15. #15
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    Quote Originally Posted by jmorgan View Post
    Just looked over my wheel to check everything and make sure it was all good and found some cracks. Here is the worst one. Notes from when I built the wheel have this one at 15 (131Kgf) on a park meter. Cracks are on the DS. Rim has a couple thousand miles maybe 4kish. These were some of the first rims released and got them from Fairwheelbikes.

    Anyone else have this happen?

    Click image for larger version. 

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    jmorgan,

    Sorry to see your rim has cracked. We will (through your point of purchase) get you taken care of.

    Fwiw, we have been keeping track of failures, and to date, of the 10,000+ SL23 rims we've sold, exactly 26 have failed. The trend in all of these failures have been low spoke count rear wheels (24h) with over tensioned spokes under heavier riders. I am not saying that is the issue with your wheel, and it's certainly not true in all cases, but so far that's been the norm in most instances.

    Nipple washers are never a bad idea, and as always, max spoke tension should be 125kgf.

    Cheers,
    KP

  16. #16
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    Quote Originally Posted by Kirk Pacenti View Post
    jmorgan,

    Sorry to see your rim has cracked. We will (through your point of purchase) get you taken care of.

    Fwiw, we have been keeping track of failures, and to date, of the 10,000+ SL23 rims we've sold, exactly 26 have failed. The trend in all of these failures have been low spoke count rear wheels (24h) with over tensioned spokes under heavier riders. I am not saying that is the issue with your wheel, and it's certainly not true in all cases, but so far that's been the norm in most instances.

    Nipple washers are never a bad idea, and as always, max spoke tension should be 125kgf.

    Cheers,
    KP
    Recommended washers-link please.

  17. #17
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    Quote Originally Posted by Bridgestone View Post
    Wh
    Recommended washers-link please.

    Round PolyAx (HM) Washers (20 pieces)

  18. #18
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    Pacenti rim cracks-ligero1.jpg

    I had the exact issue on a 24 spoke rear pacenti sl23 built by the infamous Trot Watson at Ligero Wheels. Hub is a White Ind T11. Figured I was SOL in dealing with Ligero, so I called Pacenti directly. They quickly sent me a replacement free of charge, no questions asked. Had the wheel rebuilt locally and have had no further problems so far.

  19. #19
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    Quote Originally Posted by Fignon's Barber View Post
    Click image for larger version. 

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    I had the exact issue on a 24 spoke rear pacenti sl23 built by the infamous Trot Watson at Ligero Wheels. Hub is a White Ind T11. Figured I was SOL in dealing with Ligero, so I called Pacenti directly. They quickly sent me a replacement free of charge, no questions asked. Had the wheel rebuilt locally and have had no further problems so far.
    FB,

    Glad you're up an rolling again. We aim for 100% customer satisfaction, and will do everything we can to keep our customers happy and riding Pacenti products.

    Cheers,
    KP

  20. #20
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    Quote Originally Posted by Kirk Pacenti View Post

    Fwiw, we have been keeping track of failures, and to date, of the 10,000+ SL23 rims we've sold, exactly 26 have failed. The trend in all of these failures have been low spoke count rear wheels (24h) with over tensioned spokes under heavier riders.

    Nipple washers are never a bad idea, and as always, max spoke tension should be 125kgf.

    Cheers,
    KP
    Kudos to you for acknowledging the issue, offer a solution and stand behind your product.

  21. #21
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    Valley Cyclist Wheels www.valleycyclist.com

  22. #22
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    KP: What would be Pacenti's recommended maximum rider weight when using the 24 hole SL23 rim for a rear wheel? Besides high spoke tension being a factor, does the lacing pattern used seem to make any differences in the failures that have been noted?

  23. #23
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    Quote Originally Posted by Kirk Pacenti View Post
    Sorry to see your rim has cracked. We will (through your point of purchase) get you taken care of.
    I guess the thickness of the sl23's bottom is 2mm or lower like many other of todays light aluminium clincher rims.
    So why you guys don't go up to 2.5mm or even 3mm?
    Is it for manufacturing reasons?
    Personally I wouldn't mind the weight increase of maybe 10-20 grams if I can avoid tinkering with washers.
    The SL23 would still be a nice rim with an outstanding cross section and less than 500 grams.

  24. #24
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    Quote Originally Posted by cdhbrad View Post
    KP: What would be Pacenti's recommended maximum rider weight when using the 24 hole SL23 rim for a rear wheel? Besides high spoke tension being a factor, does the lacing pattern used seem to make any differences in the failures that have been noted?
    In my opinion, 175-180 is the limit for any 24h rear wheel.

    We have had too few failures to draw any meaningful conclusions about lacing patterns as they might relate to rim failures.

    Cheers,
    KP

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    double post.

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