How do I fix a twisting seat post?

I am getting frustrated with having my seat get twisted after a fall. I have a Semcycle XL uni and have added a 2 bolt seat post clamp. I have tightened the clamp tight enough that I have made dents in the seatpost. It still twists when it takes a hard fall. Any good tips on how to keep it from twisting? Has anyone put a pin through the seat post and seat tube to keep it set straight?

In addition, any tips on getting the seat lined up straight? How critical is the lining up of the seat? Is a slight misalignment significant enough to cause riding problems?

I realize some of you never fall and drop your uni, but if you’ve heard of anyone who has, please ask them to reply to this post. :slight_smile:


I think there’s no other way to make sure that your seat post doesn’t twist than to just put a bolt through it. . You can check this little thread of mine where we had a little discussion about this: Improving seat clamp and post

Another way is to buy an anti-twist seat post from I have one on my Nimbus. It works quite well. It usually gets quite a lot of bashing but doesn’t twist. Well, maybe a little but not much. And I’m using a quick-release clamp. So probably it wouldn’t twist at all if I was using a bolt to tighten it.

Lining the seat straight is pretty important. Otherwise it can rub your thighs or you can’t ride straight. It pretty much depends on the person, if this annoys or not. I can notice quite a small misalingment on the seat but it doesn’t matter too much.

If you have put dents in the seatpost it should gall when it twists. If it galls it will be hard to take out and reinsert. If it’s not hard to take out and reinsert and it has galled, the seatpost tube on the frame is too big or the seatpost is too small or both. A shim might help your problem. Of course A-12 epoxy or welding would completely solve your problem. Phil would recommend a cattle prod but I don’t think that will help in this case.

On my standard Nimbus seatpost I use this double bolt clamp: -

And have no problems with twisting.

I did notice initially that it was tricky to get it solid i.e. I’d do it up really tight (verging on over tight) and the post would still twist.

I found it best to get the seat lined up and then alternatly tighten each bolt a small amout, going from one to the other; rather than tighten one fully and then the other.

I don’t know why this should help, but I’ve had no problems since adopting that way of doing iy.

I don’t recommend drilling holes through the seatpost or seat tube, but if you have to then drill at least two diameters below the top of the seat tube, and don’t tighten the bolt enough to crush the tubes. It should ideally fit the hole well so that the seat tube rotation is minimal, but have zero crushing force. Using two nuts jambed together would be better than one nut jambed against the frame.

Do NOT drill the hole near the seat collar. Holes tend to concentrate stresses, and this is one of the high stress areas for the seat post. Two diameters below the top of the seat tube and you’re well away from major stress areas of the seat post. The seat tube is still stressed there, however two diameters down from the top the stresses are organized well and so the hole won’t have as much effect. Drilling the hole there only reduces the strength of the seat tube by about 50%.

I’d try some other method first, like sanding the seat post and inside of the seat tube to roughen the surfaces (Plan A), or using a bit of fine sand between the two to increase the friction (Plan B).

Easy - get the three-bolt cast aluminum clamp - Darren Bedford has them, and maybe does too. Also, make sure that your seatpost hasn’t been damaged by your old clamp. I had a problem where the clamping area was relatively small and the seatpost material was soft which led to the seatpost going out of round at the clamping spot.

Maby a bit of Loctite would do the trick, should still be possible to take it apart with not too much violence.

I haven’t had a chronically twisting seat in over a year, but I may have twisted the seat on my Onza once at the muni weekend, but that’s it. I started out with a crappy united, and it twisted a lot, but then I super tightened the bolt, and now it works. I how ride an onza which takes some hard hits, and it has a 2 bolt seat clamp. I tighten each bolt a little at a time, and it works. I finally have a Muni, which can twist, although rarely (I don’t usually fall off it in a way that would twist it). I’d tighten it more, but the quick release clame is gonna snap eventually, and, I don’t want to tighten it too much, which will speed that process up.

Hey Bill,

I thought you were riding your KH, now. I have the same problem with my 29er on a YUni frame. I remember reading at one time someone had suggested putting talcum powder on the seatpost and then inserting it. I was going to try that, not sure if it works, though.

Have fun!


I am riding the KH24 now, and I love it!, but only outside. I am riding the Semcycle XL inside. I replaced the knobby tire and metal pedals with the original parts and am working on freestyle too. I can ride at the gym of the fitness center where I work out. Lately, I ride more than I work out at the gym.

I’m slowly building up the uni inventory so I can have a specialized uni for each type of riding. That is one of the key goals for a uni rider, isn’t it?

He who has the most toys, wins! :smiley:


ah i’m not the only one!

it’s really annoying it happens to me to i got my dad to tighten my seatpost loads and it’s been a lot better but it’s really annoyig because my seat goes all wonkey and i end up riding wonkey

I’ve got a good way to stop the seat post from twisting. I send my seat post down to the workshop and got the guys there to knurl it. After that, the seat post just stop twisting… :slight_smile:

A GB seatpost has been my solution. They are stronger and thicker and don’t crease the way the stock ones do. In addition, I don’t usually use a quick-release clamp; I just carry a bike multi-tool wherever I ride.