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Old 07-03-11, 07:17 AM   #1
hule
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quick release seatpost turns in seat tube?

so i have a bike and it is hard to find a proper size seatpost and i settled for a steel one that is about the right length (could be longer) and can fit in the seattube (also steel), it is not too big but slightly too small. i can close the quick release clamp (i need to take the seat with me cause it is expensive) however i can still turn the seatpost slightly, this can happen when riding. now i don't think the seatpost is sinking but i haven't taken it for a long ride yet. now what about the turning, i take it that can't be good for the bike in the long term, is that right? are there any solutions?
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Old 07-03-11, 07:47 AM   #2
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Go to a bike shop and get a seat post shim.
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Old 07-03-11, 08:02 AM   #3
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Go to a bike shop and get a seat post shim.

read my post next time before you post. i take my seat with me.
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Old 07-03-11, 08:59 AM   #4
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Originally Posted by hule View Post
so i have a bike and it is hard to find a proper size seatpost and i settled for a steel one that is about the right length (could be longer) and can fit in the seattube (also steel), it is not too big but slightly too small. i can close the quick release clamp (i need to take the seat with me cause it is expensive) however i can still turn the seatpost slightly, this can happen when riding. now i don't think the seatpost is sinking but i haven't taken it for a long ride yet. now what about the turning, i take it that can't be good for the bike in the long term, is that right? are there any solutions?
The post turning in the frame won't damage anything. However damage might occur if you start tightening the quick release to keep the seatpost from slipping. If the quick release is a collar, that's not going to be an issue since you can always replace the collar. If the quick release is part of the frame, you could eventually crack it if you overtighten.
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Old 07-03-11, 09:39 AM   #5
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The post turning in the frame won't damage anything. However damage might occur if you start tightening the quick release to keep the seatpost from slipping. If the quick release is a collar, that's not going to be an issue since you can always replace the collar. If the quick release is part of the frame, you could eventually crack it if you overtighten.
this doesn't make sense, the quick release is a separate bolt like this:



i have one of these on my bike, it is attached through the hole through two "tabs" permanently attached to the seattube.
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Old 07-03-11, 09:55 AM   #6
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Step one look at the seat tube slot when the seatpost is clamped. With a properly sized post the slot will be pinched closed slightly at the top. With an undersized post there will be more pinching, and if the post is much too small the top will be closed on itself and the post cannot clamped tighter no matter how hard you try.

If the slot closes to touching or nearly so, buy the right size post. Period

If the slot still is 1/16" wide at the top, a better collar or QR unit might do the trick, though your best bet is to paint the 2" section of the post which ends up under the clamp with something that will improve traction.

Carbon assembly paste will work, but something less expensive like latex paint might also. Before painting be sure to strip the post to bare metal with acetone (not nail polish remover), naphtha, or mineral spirits which will leave it clean, dry, grease free and ready for the coating to stick.
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Old 07-03-11, 10:01 AM   #7
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Quote:
it is not too big but slightly too small.
,

by exactly how much? given: there is a seat post sized in 0.2mm increments of diameter

I migrated a 25.0mm seat post to a 27.2mm bike, by buying the appropriate shim [USE made(UK)]
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Old 07-03-11, 11:46 AM   #8
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this doesn't make sense, the quick release is a separate bolt like this:



i have one of these on my bike, it is attached through the hole through two "tabs" permanently attached to the seattube.
It's the tabs that can crack. The quick release isn't just the bolt but the mechanism used clamp the post in place. The tabs are part of that mechanism. If you crack the tabs, the frame is basically ruined. (It could be repaired by the cost might be more than the bike is worth.)
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Old 07-03-11, 12:18 PM   #9
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if the tabs crack (and not the seat tube) can't i cut down the tabs and use a seatpost collar?
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Old 07-03-11, 12:33 PM   #10
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Quote:
Originally Posted by hule View Post
if the tabs crack (and not the seat tube) can't i cut down the tabs and use a seatpost collar?
hule: wouldn't it be more straightforward to just use the right seatpost?
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Old 07-03-11, 12:41 PM   #11
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Quote:
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if the tabs crack (and not the seat tube) can't i cut down the tabs and use a seatpost collar?

Possibly, but it's sometimes impossible, and sometimes not easy. Three possibilities

1- the plain seat tube extends above the weld by over 1/2" . A collar will work, no problem after you've cut off the ears and cleaned up any remaining part of them.

2- the seat tube extends beyond the weld but the ears are part of a brazed on ring at the top of the tube. This is more of a problem because the OD of the ring may not match any available collars. A collar is still an option, it's just more difficult.

3- the ears are part of a lug that doesn't extend beyond the top of the top tube (classic road bike construction). There is no place for a collar, so breaking of an ear is a serious issue, repairable only by praxing a replacement.

As I posted earlier, the width of the slot when clamped is the key. If you're able to clamp the post just shy of tight enough, odds are the slot is closed at the top, or the ears are touching. That means the post in undersized by close to 1mm (3mm slot closed to 0 divided by Pi). If the ears touch but the slot is still open a bit it's a bit less.

The issue isn't wear from a moving post, but the excess stress placed on the ears trying to clamp beyond the design limit. If the ears aren't touching, traction material on the post may be all that's needed, otherwise your best bet is to do what you can to either find the right post, or shim it to size.

Depending on how much shimming you need, you might consider stainless steel shim stock and super glue. Glue the shim to the 4" (to prevent rocking) of the post just inside the frame when the saddle is at the right height. Shim stock is available in a large variety of thicknesses, and easy to work with. To get a good glue job, hold it all together with 3-4 hose clamps while the glue cures.
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Old 07-03-11, 12:43 PM   #12
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hule: wouldn't it be more straightforward to just use the right seatpost?
That's too obvious, and then we wouldn't need the forum.
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Old 07-03-11, 02:58 PM   #13
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if the tabs crack (and not the seat tube) can't i cut down the tabs and use a seatpost collar?
That's a lot of work to go through. You'd have to cut off the tabs, grind the old welds off, make sure that the metal is cleaned up and round, and find a seatpost collar that will fit. Finding the right collar might be more trouble than finding the proper seatpost.
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Old 07-03-11, 03:04 PM   #14
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Kalloy makes all OD of seat posts from 25.0mm to 27.2, in 0.2 mm increments,
and are stocked by most wholesale distributors in the food chain..
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Old 07-03-11, 03:29 PM   #15
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A hearty +1 on just getting the correct seat post and solve all your troubles in one easy AND PROPER solution.

When you pinch in the tabs in to force a grip on a post that is a size or two sizes too small you create the very problem you're experiencing of not having enough contact area to provide the friction needed. This occurs because with too small a post the clamp deforms the seat tube into a cone like shape which only grabs the seat post around a thin ring at the top of the seat tube opening instead of a broader cylindrical grip such as using the correct size post would provide. So to get it to avoid creeping or turning in that grip you end up having to tighten your clamp all the harder. But as you're seeing this isn't working for you. In addtion with the seat post being too small it's free to wobble sideways in the seat tube down lower. And when you allow the post to wobble that way it's just a matter of time until it walks its way down the seat tube past the clamping line and sinks slowly under your weight.

The answer is very clear. Get the proper size post. It'll fix all the issues you currently have as well as some haven't noticed yet due to you removing your saddle each time you park the bike. Never mind the idea of a tighter clamp or what to do if or when your present tabs deform too far. Get the proper seat post and you'll find that it clamps tightly with less lever force as well as avoiding any future frame damage.
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Old 07-03-11, 05:14 PM   #16
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read my post next time before you post. i take my seat with me.
This is why I seldom reply to posts. I offered a valid solution to your problem, regardless how you clamp the post it appears to be too small. Anyway, for my trouble all I get in return is a snide remark. Thanks.
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Old 08-10-11, 06:17 PM   #17
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This is why I seldom reply to posts. I offered a valid solution to your problem, regardless how you clamp the post it appears to be too small. Anyway, for my trouble all I get in return is a snide remark. Thanks.
of course, you didn't even read the original post so your reply made no sense. next time write a valid answer and then maybe you will get a better response.

back on topic, i fixed the problem.
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