Hi there. I have a Coker Big One, and a Kris Holm rail type seatpost to attach my T7 handle. When I mount, the seatpost will twist to the right, and I can’t ride far before stopping with a wall to re adjust. I have it tightened as much as I physically can, but it will still turn. Any suggestions?
Don’t hold the T7 handle when mounting, just hold the front of the seat. This will greatly reduce the torque that’s being applied during mounting. If that’s the only time your seat twists, it might be enough. Otherwise you may want to look into a 2-bolt seat clamp.
It may not be the seatpost twisting in the frame.
On the original KH rail posts the clamp (silver bit that holds the T7) was a press fit into the top of the post, and sometimes this joint became loose, particulary if used with a T7. Later KH rail posts are pinned at the joint between clamp and post to prevent this.
You can easily check if it’s the post turning in the frame or the clamp moving in the top of the post by noting the postition of the writing on the post relative to the frame before you start riding, and after the seat twists.
If it’s the clamp moving in the post it’s simple to fix, either buy a later post with the pin fitted, or if you have the tools drill a hole through the post and clamp and put a thin bolt through.
The weird thing is that I do have a 2 Bolt. And the pin. And still, I can easily twist it with my hands. It didn’t happen before I got the Kris Holm.
It’s possible your new seat post is not the correct size for the seat tube. I don’t know the measurements offhand, but if it’s off by 1mm it may not look wrong, but it may be a problem to keep it tight. If the slot in the seat tube is closing nearly all the way, or if your clamp is closing all the way (no gap where the bolts go through) it means something isn’t fitting right.
Is the post twisting in the frame, or is the insert twisting in the post?