coker seatpost issue

[gratefulbruce]

I recently inherited a set of T7 handle bars to try on my old (all steel) Coker. This weekend I went to the bike shop and got a new seatpost (22.2), and moved the seat over to the new post, installed bottle cages etc. I clamped the new setup into the frame (the clamp is the single half turn type of clamp used on bicycle forks), and found I could not get the clamp on tight enough to keep the setup from turning in the frame. I looked at the old seat post, and saw there was a crisscross knurled pattern in the post, and the new post is smooth. I am wondering if there is any experience on this site with this, and would simply changing out the single clamp half turn with a two nut sleeve style clamp probably be enough to stop the seatpost slippage? I also have a dremel tool, and was thinking of trying to cut some grooves into the new post, but that sounds like a lot more work than just getting a different clamp or different seatpost. Any experience would be helpful, thanks for your input.

[tstessney]

I wouldn't do the Dremmel Tool thing. You should be able to tighten the quick-release seat post clamp by either turning the nut (clockwise) on the opposite end of the lever (if it has a nut - some are "nutless" where the bolt threads directly into the other side of the clamp), or by turning the lever itself (clockwise) to tighten it. When you throw the lever to the closed position, it should take a fair amount of "oomph" to close it, thus preventing the seat post from twisting. But don't overtighten it or you'll snap the bolt or the clamp itself - it's a fine line between loose and broke.
If the problem is that the post is VERY loose, meaning that it rattles around inside the frame tube, you may have the wrong size seatpost. You may need a 25.4 post instead of a 22.5.

[jtrops]

When your QR is adjusted correctly you should start to feel resistance when the lever is half way through it's travel. If you need it to be tighter than that there are other problems. If it is an internal type QR you can use light oil, or Tri-Flow in the cam to make it move more easily. If it is an external cam you can put a thin coat of grease on it. That can help with the lever moving without feeling like you might break it. Changing to a bolt type clamp could solve your problems. There are a lot of people who have complained about QR's not holding their seats tight enough. 22.2 is the correct size for the old Coker frames, so you got that right, and I wouldn't put grooves into the post you have as it will decrease the surface area for the seat tube to grip.

[justtysen]

This may be irrelevant but I noticed that the seat post that comes with the newer Coker frames while designated 25.4mm is actually ever so slightly larger, so that when I used an actual 25.4mm seat post I had to over-tighten the clamp. They may have done something similar with the older frames and seat posts too. In which case my advice is to order some bmx style seat clamps without the ridge and stack them to get a high clamping force. Maybe like this from unicycle.com.


Also, you have to realize that the handlebar allows more torque on the seat post so even the same clamping pressure as before might not hold it tight. Which some people are okay with as it means the setup will twist rather than cause permanent damage during a crash.