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.

Bill


--
billham

Direction is everything, distance is secondary.
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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_' (http://tinyurl.com/wwh9)

Another way is to buy an anti-twist seat post from unicycle.com. 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.


--
joona - )-O --Neat

Mad as a moose (or atleast Minimoose)
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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.


--
harper - Old dog, no tricks

-Greg Harper

B L U E S H I F T

"I managed to get my missus riding a couple of yards before she got
pregnant with Jenny, but she hasn't tried riding since. " - Danny
Colyer

"Sa da tay! Sepotown!" - Pootie Tang

"Know thyself. Of course, try to know Claudia Schiffer and Salma Hayak
but, failing that, at least know thyself." - Greg Harper


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

http://tinyurl.com/wwko

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.


--
onewheeldave - Semi Skilled Unicyclist

"He's also been known to indulge in a spot of flame juggling - but it's
the Muni that really fires him up."

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joona wrote:
*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_' (http://tinyurl.com/wwh9)
*

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).


--
cyberbellum - Level 0.5 rider

If I knew what I was doing I wouldn't be in research...
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Easy - get the three-bolt cast aluminum clamp - Darren Bedford has them,
and maybe Unicycle.com 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.


--
KnowFear

Chris... who DOES have a WMD (Wheel of Mass Dismounts).
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Maby a bit of Loctite would do the trick, should still be possible to
take it apart with not too much violence.


--
omdetdar - getting better
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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.


--
gerblefranklin

I don't break equipment, I make it cheaper.
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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!


--
teachndad - The Munieer

Rod Wylie

You don't have to be a fantastic hero to do certain things -- to
compete. You can be just an ordinary chap, sufficiently motivated to
reach challenging goals. - Sir Edmund Hillary

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Rod

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!

Bill


--
billham

Direction is everything, distance is secondary.
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