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seatpost slipping(5 posts)

seatpost slippingnot_lost
Apr 10, 2003 4:48 PM
I have a 2002 Colnago Classic with a Thomson seatpost. The seatpost slips no matter how tight I make the seatpost clamp bolt. I've broken many bolts by overtightening. I even cleaned all the grease off the post and out of the frame. It still slips. Are some seatposts slightly larger than others eventhough they are listed as being the same size? How do I stop mine from slipping?
Probably too small diameterKerry
Apr 10, 2003 5:22 PM
Go someplace that has precision tools and measure the post and the seat tube diameter. I'll bet you'll find the post is 0.2 mm too small. Could be just mis-labeled, but the effect is the same.
other posibilities...C-40
Apr 10, 2003 6:51 PM
If your seatpost does not measure 27.2mm or 1.071 inch, then replacing the post with the proper size should fix the problem, unless the clamp has been stretched. Be sure that the clamp has some small gap in the middle when the post is tightened.

Another posibility is bottoming out the clamp bolt. If the clamp has been stretched from over tightening, the clamp bolt may bottom out, which will break the bolt much easier. There should also be a small gap between the two halves of the clamp bolt when it's fully tightened. If there is no gap, then install one or two washers from the many bolts that you have broken.
C-40's got ittarwheel
Apr 11, 2003 5:49 AM
Here's the problem. Most of the newer bikes have oversized tubing and seatpost binder bolts (I presume) have been made longer to compensate for that. So, the bolts tend to bottom out on frames with smaller tubing before you can fully tighten them -- and then they snap. I had this happen a number of times on my steel frames until someone told me to try adding some washers to the bolt. Voila -- problem fixed. Simple, inexpensive fix. Also, speaking from experience, carry a spare binder bolt w/washers in your seat bag just in case.
re: seatpost slippingkenyonCycleist
Apr 10, 2003 10:01 PM
have u checked to make sure the post has not been crunched, even a slight alteration of the post-diameter can render the post like a cone so it slips no matter what