Quill seatpost can cause tube bulge, so how tight is TOO tight?
08-16-16, 03:22 PM
#1
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Quill seatpost can cause tube bulge, so how tight is TOO tight?
How should I go about possible over-tightening a quill seatpost? I guess its the insecurity thats sinking in, never had a quill seatpost, and reading about possible 'bulging' doesn't sound very nice, given the fact that I REALLY like my bike. So, whats the rule of thumb to go about this? Don't have a torque guide, nada. So, tighten till I can't tighten with my hands? Or should I use a handle-bar stem torque as a guide?
08-16-16, 03:28 PM
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I use green Loctite 609 in the seat tube in conjunction with quill seatpost, and get it as tight as I can torque with a 4" allen and no cheater - it's held for thousands of miles
08-16-16, 07:20 PM
#4
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some type of sleeve, tubing to make 4" allen longer for more leverage
08-16-16, 07:41 PM
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see this:
Notice it doesn't appear he's using much force at all to lock in with the allen wrench.
Notice it doesn't appear he's using much force at all to lock in with the allen wrench.
08-16-16, 08:04 PM
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The same rule of thumb applies here as everywhere else.
Tighten everything tight enough to do it's job and no more.
It's a seatpost, and all you care about is that it doesn't slip. Once it's tight enough not to slip, tightening it any more can't make it slip any less than zero.
In fact many older timers and race mechanics, use a variation on this called "race tight". On a post you want to be sure that it can't slip or twist in normal, or even rough use, but can still twist at extreme loads as might happen in a crash. This can prevent saddle rails from twisting, or more important, reduce bruising between your legs if you go down badly in a crash.
Opinion follows.
I am not at all a fan of expander posts, especially sliding wedge types. They can over stress and (as noted) bulge thin wall seat tubes. They violate one key tenet of good design, namely that failure should be planned for and managed such that the cheaper part always fails first. Another tenet is that there should be the widest possible margin of error separating tight enough to do the job, and tight enough to fail.
IMO combining this post with a thin tube imposes a narrow margin. It can be widened by improving traction between the post and tube, and (obviously) by using a seat tube with a thicker wall.
Tighten everything tight enough to do it's job and no more.
It's a seatpost, and all you care about is that it doesn't slip. Once it's tight enough not to slip, tightening it any more can't make it slip any less than zero.
In fact many older timers and race mechanics, use a variation on this called "race tight". On a post you want to be sure that it can't slip or twist in normal, or even rough use, but can still twist at extreme loads as might happen in a crash. This can prevent saddle rails from twisting, or more important, reduce bruising between your legs if you go down badly in a crash.
Opinion follows.
I am not at all a fan of expander posts, especially sliding wedge types. They can over stress and (as noted) bulge thin wall seat tubes. They violate one key tenet of good design, namely that failure should be planned for and managed such that the cheaper part always fails first. Another tenet is that there should be the widest possible margin of error separating tight enough to do the job, and tight enough to fail.
IMO combining this post with a thin tube imposes a narrow margin. It can be widened by improving traction between the post and tube, and (obviously) by using a seat tube with a thicker wall.
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FB
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An ounce of diagnosis is worth a pound of cure.
“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 08-16-16 at 08:14 PM.
08-17-16, 01:56 PM
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My youngest brother just never learns.....
He tightens fasteners to his personal, biological, "quivering hands and arms" tourque limit........ which is usually followed by a loud snap and "RATS!!" From where ever he happens to be working on something......
He tightens fasteners to his personal, biological, "quivering hands and arms" tourque limit........ which is usually followed by a loud snap and "RATS!!" From where ever he happens to be working on something......
Last edited by Chombi; 08-17-16 at 02:27 PM.
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08-17-16, 02:25 PM
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I have always just used a four inch allen like Bulldog said. But never used locktight, just greased the post like I would any stem. Its never slipped, so far with just regular hand tightening. Mine is in an aluminium schwinn 974.
08-17-16, 02:33 PM
#9
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I believe it was a park tool, longer than 4 inches.. From the looks of it, the bolt that tightens the seatpost doesn't seem to be protruding A WHOLE lot so I think I might be in the clear? Ive searched to see how others seat posts were looking online and looks pretty similar. I was going by those pictures as a guide loll.
08-17-16, 02:35 PM
#10
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Rekmeyata, I have watched that clip, however HIS 'tightest point' seems A LOT less than mine. I was going atleast 4-5 full circles. His was maybe more or less than 90 degrees. Wish mines was that easy.
08-17-16, 02:39 PM
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We have an expression here that would translate into something like: 'tight is tight enough". It means that one shouldn't tighten a bolt any more than necessary. In practice it means that you should use less force than you might be inclined to do. I have found that to be very sound advice.
08-17-16, 02:49 PM
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08-17-16, 03:11 PM
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Tighten everything tight enough to do it's job and no more.
BE CAREFUL would be my approach to using a quill seat post on any of my bikes. Plus, on a regular bike, only the lugged area is actually applying force to clamp the post is the seat tube lug. There are so many things to consider.
For my money, or lack of it (I am married with kids and grand kids), I probably won't be using a quill seat post ever. Of course, this Skyway does use a quill post and it is still in Thunder Bay and I really like the bike...
But it is not made of exotic thin walled tubing.
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