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Thread: My seatpost clamp is too big right?

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    Default My seatpost clamp is too big right?

    Had a custom frame made 18 monthsish ago and recently Iíve been having trouble with the saddle slipping - itís a steel frame and alloy post but I feel like I have to put way too much on the bolt to prevent it sliding down.

    It looks to me like the clamp is too big - there should be a gap between the ends right?

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    Default Re: My seatpost clamp is too big right?

    That looks a little big. I would measure with a caliper and see about getting the next size down.
    Steve Hampsten
    www.hampsten.blogspot.com
    "Tighten the wingnuts!"

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    Default Re: My seatpost clamp is too big right?

    Too big or post is crimped.
    -Dustin

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    Default Re: My seatpost clamp is too big right?

    Was there ever a shim in the seat tube?

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    Default Re: My seatpost clamp is too big right?

    There still is a plastic shim in there - it was always like that.

    Definitely not crimped post either - I coincidentally just changed it to a different setback and itís the same.

    I think they just gave me the wrong one when I collected the frame - I supplied the seat post (to their spec and itís a decent fit) so it would be easy not to notice that it was a size too large.
     

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    Default Re: My seatpost clamp is too big right?

    Perhaps you’ve squashed the plastic shim? Probably not as I’d guess it’s Delrin, which is pretty hardy; but it’s something to eliminate.

    Otherwise, I’d guess they’ve given you the wrong one, yes. Measure the width of the seat tube with calipers, then measure the internal diameter of the clamp when loose - that’ll give you your answer.

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    Default Re: My seatpost clamp is too big right?

    That's not good.
    At some point that bolt will fail due to the tension that is bending it.

    What is the original size of the seatpost ID? Do you really need a shim?
    If was me, I'd get the right size of seatpost in the first place. Failing this, I'd replace the shim and find a different seat collar (the taller, the better)
    Andrea "Gattonero" Cattolico, head mechanic @Condor Cycles London


    "Caron, non ti crucciare:
    vuolsi cosž colŗ dove si puote
    ciÚ che si vuole, e piý non dimandare"

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    Default Re: My seatpost clamp is too big right?

    I think you have a 31.8 DKG but what you need is a 30.0

    If it's an externally butted 1.125" / 28.6mm seattube then 30.0mm is very common

    If your ST is 1.25" then 31.8

    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: My seatpost clamp is too big right?

    Think I have all the relevant measurements:

    The ID with the delrin tube (which is in fine condition) is 27.1 (and a bit if you squeeze the caliper - so seems the correct size for the seat post)

    The seat tube OD is 32.5

    (without the sleeve the ID is 30.4 - so a weird size for a seatpost?)

    With no bolt the clamp is 32.8 - and it's definitely quite a loose fit - it rattles around when you just put it over the tube.



    I took the clamp off another bike and it measured 31.7 (so probably a 31.8) and it wouldn't quite fit.



    So, I'm still a bit stumped on what to do - it seems to be an unusual size.

    Is the answer a 31.8 that hasn't been clamped to anything and it should fit over the tube? Did find a Chromag clamp which says it's 32.0 - .2mm might be enough to fit? Or do custom builders get more options and I should just see if they have one inbetween those sizes?

    Thanks a lot. Spent way too much time thinking about this today when I should have been riding my bike...
    It's not the years, honey. It's the mileage.

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    Default Re: My seatpost clamp is too big right?

    Quote Originally Posted by steve garro View Post
    If your ST is 1.25" then 31.8

    - Garro.
    Thanks, just saw this - I get 32.5mm to be about 1.28" - I guess that's a 1.25" tube and the thickness of the paint?
    It's not the years, honey. It's the mileage.

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    Default Re: My seatpost clamp is too big right?

    Quote Originally Posted by kdawg View Post
    Thanks, just saw this - I get 32.5mm to be about 1.28" - I guess that's a 1.25" tube and the thickness of the paint?
    Man......maybe really, really thick paint?

    I send out DKG 31.8's on every single bike and never had one slip ever.

    Kind of a janky fix but you could widen the slot.......next step is beer can shim........?

    Maybe an aluminum sleeve as the delrin one is slippery ???


    - Garro.
    Last edited by steve garro; 08-25-2019 at 02:17 PM.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: My seatpost clamp is too big right?

    Your insert/adapter should have a slot as well. Is that slot JUST SLIGHTLY misaligned with the seat tube slot? It should be. It keeps gunk from reaching the seatpost.

    The flange which keeps the insert from slipping into the seat tube-it's possible this flange is contacting the top I.D. of the clamp before the clamp can do its job on the seat tube itself.

    To prove it, slide the insert so it is just above the clamp, and secure the clamp. If the saddle stops slipping, you have your answer. At that point, I imagine your solution would be to either increase the I.D. of the lip of the clamp or reduce the O.D. of the lip of the insert, with sandpaper.

    I wonder if you've already damaged the clamp.

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    Default Re: My seatpost clamp is too big right?

    Yeah, itís already purposely misaligned for the reason you said.

    I didnít say but I tried that earlier too - I switched the order so the lip of the insert was above the clamp to see if something was interfering with it - no difference, as in my first picture the clamp
    Basically bottoms out with barely any pressure - and I guess the cranking Iím having to do is distorting the clamp enough to squeeze the tube.

    Now that Steve has pointed out the brand (I couldnít interpret the dkg which seems obvious now) it looks like I have a 33mm clamp and their next one down is 31.8 - it definitely feels like 1mm or so of slop so that size might be just right.
     

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    Default Re: My seatpost clamp is too big right?

    Quote Originally Posted by kdawg View Post
    Now that Steve has pointed out the brand (I couldn’t interpret the dkg which seems obvious now) it looks like I have a 33mm clamp and their next one down is 31.8 - it definitely feels like 1mm or so of slop so that size might be just right.
    You got one of the 33mm Columbus dropper tube ones.

    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: My seatpost clamp is too big right?

    If willing to keep that seat collar, I'd replace the bolt right away. It's certainly weakened by now.

    The possibility that the ID lip of the seat collar touching the seatpost can be easily checked: if that's happening, the seatpost will get scratched and the ID lip of the collar will look worn down (at least in the anodization).

    A quick fix -all else been working well- can be the use of a thin shim between the seat tube and the seat collar.
    In the workshop I always have pieces of 0.10 and 0.05mm stainless sheet, that stuff is miles better than "beer can shim"; stainless is hard enough and will last forever, while the aluminium of a can is awful metal that's soft and will dissolve with time. The latter is only useful for a quick fix to see if works, or to find the culprit.
    Andrea "Gattonero" Cattolico, head mechanic @Condor Cycles London


    "Caron, non ti crucciare:
    vuolsi cosž colŗ dove si puote
    ciÚ che si vuole, e piý non dimandare"

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    Default Re: My seatpost clamp is too big right?

    Burn the whole bike and buy a new one. This one wants to kill you.

    --
    T h o m a s

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    Default Re: My seatpost clamp is too big right?

    Thanks for all the help. Fixed now. The day after my posts I decided to check the seat tube external measurement again as it didnít seem right - got 32mm that time - 0.2mm for paint still maybe a bit much but obviously closer.

    Anyway got a 31.8 clamp and with the bolt removed it slipped on with just a little persuasion (and paint from the lip). Felt much better when I tightened it. The only thing I donít like is that this one isnít quite so tall so you can see a mark where the old one was and the gap this time is quite big - just donít like the way it looks!

    But back on the road and no slipping.

     

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    Default Re: My seatpost clamp is too big right?

    Buy a DKG

    It won't stretch or slip and covers the gap you see / has a lip / is super hard ano.

    I've sent out so many hundreds of them and never seen one come back.


    - Garro.
    Steve Garro, Coconino Cycles.
    Frames & Bicycles built to measure and Custom wheels
    Hecho en Flagstaff, Arizona desde 2003
    www.coconinocycles.com
    www.coconinocycles.blogspot.com

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    Default Re: My seatpost clamp is too big right?

    Yeah, that’s my plan, it ticks the boxes for looks and effectiveness.
    It's not the years, honey. It's the mileage.

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    Default Re: My seatpost clamp is too big right?

    Now how about some pictures of the bike.

    Mike
    Mike Noble

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