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  1. #1
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    Seat post breaking frames?? HELP!

    Hello gents!

    I just had my second flash 29 aluminum frame replaced in less than a year. Both frames failed in the same place, where the seat post and top tube are welded ( see pics ).
    2012 frame


    2013 frame


    Here's some background... I'm about 200lbs, I ride in Illinois so the trails I ride aren't extreme, the seat post is WELL inside the proper level of extension as I'm 5'8 with a short inseam. I ride 1-2 times a week 15-20 miles a ride.

    My question is- can it be the rigidity of my Thompson Masterpiece seatpost causing these frames to fail??? Would a less ridged seat post solve this?! Can anyone suggest a more forgiving post???

    I don't think I ride overly aggressive, I don't crash, I don't jump, my ass is off the seat for 70-80% of trail irregularities and all big roots and rocks...

    I don't want to change brands as I love the fidgetiness/ quickness the frame offers but I don't want to replace my frame every year.


    Thanks to excellent service from Dans Bike Shop in Berywn IL and excellent product warranty I haven't been off the saddle more than a week either time...
    Last edited by rz79; 07-30-2013 at 11:21 AM.

  2. #2
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    < crickets > 108 views.. Sigh.

  3. #3
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    I can't offer anything other than I cracked my 2011 flash frame in the same spot and now have the same 2013 frame as you. All I can say is, at 6'3" 230lbs of fairly aggressive rider, I hope I don't end up in the same situation. If so, I'm switching brands.

  4. #4
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    I'll bite:

    Theorically, a ultra stiff post that has no flex at all could be preventing the frame's purpose-designed flex in that area. The top tube's shape (getting wider but smaller when seen from the side as it approaches the seat tube), plus the seatpost's 27.2mm diameter are meant to flex a bit fore and aft (but not side to side) to improve comfort. If the seatpost doesn't let the frame flex as it's meant to (which, theorically, might be even worst if the seatpost goes too far down into the frame), well yes, it could put more stress in that area of the frame. You should still get a warranty replacement though. Cannondale, as far as I know, have not published any restriction of un-approved seatposts so even if my theory is true (which I never thought or read about before seeing your thread), Cannondale should take care of you again.

    Personally, I think a flexier post (which nowadays pretty much everyone, riders and bike designers/engineers alike prefer) might prevent this. I don't think it needs to be SAVE flexy (the SAVE feature is a zone out of the frame anyway) but a little flex might let the frame work when hitting bumps, give you more comfort and honestly, you'll probably wont feel any difference.

    And as you know, seatposts need to be inserted deep enough (minimum mark on the post but another rule is they should end a bit under the bottom of the top tube once installed) but I've seen some too long seatposts, that their ends were rubbing the inside of the frame over sharp bumps, never seen it damage a frame but cause some noises. On some frame designs it doesn't matter but if the frame is meant to flex there and that the seat tube has a very constant inside diameter and is very close to a long seatpost, I'd cut the un-needed length (keep at least the same amount to be inserted as the length of the tip-to-minimum-mark, maybe an extra inch to give you a bit of adjustment if you change the saddle model or something).

    Keep in mind, I haven't done any tests and I'm no engineer (although I have some physics science studies) so when I say 'theorically', I mean it's what I think might be happening but I can't guaranty it's what is causing the break or not...

    My two crickets... I mean cents.

    DAN.GEROUS.NET : MOUNTAIN BIKING : CYCLOCROSS : ROAD :

  5. #5
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    Your insight / theory/ experiences are very helpful, I thank for taking the time to type them.

    As for replacement, I had a new frame in like 72hrs, I guess the rep asked if a was a "big dude" which the shop owner explained I wasn't. Other than that he had zero issues warranting it for me.
    I asked if it happens again am I screwed and the shop owner pretty much explained that it didn't sound like I had anything to worry about. He then said in 20 years of selling cannondale a he's seen 4 broken frames, two were mine. Hopefully third times the charm

  6. #6
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    Quote Originally Posted by rz79 View Post
    Your insight / theory/ experiences are very helpful, I thank for taking the time to type them.

    As for replacement, I had a new frame in like 72hrs, I guess the rep asked if a was a "big dude" which the shop owner explained I wasn't. Other than that he had zero issues warranting it for me.
    I asked if it happens again am I screwed and the shop owner pretty much explained that it didn't sound like I had anything to worry about. He then said in 20 years of selling cannondale a he's seen 4 broken frames, two were mine. Hopefully third times the charm
    Maybe you were just very unlucky. But, third time is always the right one... well, it is in classic cinema theories at least!

    DAN.GEROUS.NET : MOUNTAIN BIKING : CYCLOCROSS : ROAD :

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