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Clamping a Dropper Post


Mountain Bru
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Calling on all bikehub experts....

 

How do you guys with dropper posts (and carbon frames) clamp your bike in a bike stand when you wash it or work on it?

 

Obviously the top tube isn't an option, but clamping the dropper stanchion makes me cringe, and I'm not sure if the dropper seals etc were designed for tension forces.

 

I don't have enough exposed "non-stanchion" on my dropper to clamp, and I'm really not keen on having to adjust my seat post every time I want to put it on the work stand. I know it's just one screw, but it's more the challenge of setting the height and getting the saddle straight afterwards. 

 

What do you guys do? Any horror stories of destroying your dropper in your work stand?

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I watched this, but it didn't really help. Basically all I learnt is that the seatpost clamp clamps tighter than a work stand. But obviously this doesn't really help in knowing if it's good for the dropper to be clamped. 

 

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I always clamp straight on the stanchion. Make sure the clamps are clean. 

 

I'm quite sure the post can handle a 12kg weight (hanging fully extended) on it if it can handle a 100kg rider pushing down on it. 

 

In 10 years of riding with dropper posts I haven't had a single one show any signs of failure or even the slightest damage from clamping. 

Edited by Steady Spin
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Two options - one, clamp the stanchion. Make sure the clamp and stanchion are clean, and put a cloth between the clamp and the stanchion.

 

Two, mark your seatpost height with black insulation tape and pull the post out to the minimum insertion mark.

 

Option 1 is fine for washing and light adjusting, but for anything where you're going to be applying a decent load the second is best.

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You will find 2 schools of thought, youtube offers both that you can clamp and that you should not. Personal decision for us mortals.

I bought new jaws for my work stand then cut the old set shorter and now clamp below the shaft. I prefer to have zero risk of damage.

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Two options - one, clamp the stanchion. Make sure the clamp and stanchion are clean, and put a cloth between the clamp and the stanchion.

 

Two, mark your seatpost height with black insulation tape and pull the post out to the minimum insertion mark.

 

Option 1 is fine for washing and light adjusting, but for anything where you're going to be applying a decent load the second is best.

 

 

 

what he said ^^

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why is top tube not an option?

 

 

Not possible for al bikes. For example the 2017 to 2020 Scalpel has a top tube that tapers from head tube to seat tube and has a kink in the center span where the shock connects to the top tube. Getting a secure purchase on the top tube is almost impossible.

 

I clamp the  Dropper post stanchion. For any work requiring leverage I lower the bike so that the wheels are on the ground, loosen what needs to loosened then lift the bike up in the stand so I can work on it. 

Edited by DieselnDust
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I clamp mine on the stanchion - just clean it and put a cloth between the clamp and seatpost. The forces of you sitting on the saddle is much more than what is cause by the bike hanging.

 

When I put force down, eg: removing a crank, I always have the bike standing on the ground anyway - so can't say that's ever been a consideration for me.

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I always clamp straight on the stanchion. Make sure the clamps are clean. 

 

I'm quite sure the post can handle a 12kg pull on it if it can handle a 100kg rider pushing down on it. 

 

In 10 years of riding with dropper posts I haven't had a single one show any signs of failure or even the slightest damage from clamping. 

 

Difference is that the force from the 100kg rider is supported by hydraulic oil in a presumably aluminium chamber. The 12kg pull is potentially supported by a rubber seal. Tension and compression aren't the same when it comes to these hydraulics 

 

Glad to hear that you haven't had any issues though

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You will find 2 schools of thought, youtube offers both that you can clamp and that you should not. Personal decision for us mortals.

I bought new jaws for my work stand then cut the old set shorter and now clamp below the shaft. I prefer to have zero risk of damage.

 

 

How wide is the clamping area on your modified jaws? I though of making an insert for my jaws that only clamps between the non-stanchion are, but I only have about 3cm of room there. 

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Difference is that the force from the 100kg rider is supported by hydraulic oil in a presumably aluminium chamber. The 12kg pull is potentially supported by a rubber seal. Tension and compression aren't the same when it comes to these hydraulics 

 

Glad to hear that you haven't had any issues though

 

Having stripped and serviced a number of posts I can confidently say that it is more than a just a rubber seal supporting the pull force on the post. 

These posts are built very well. 

 

I'm not a mechanical engineer though and my decision to clamp the way I do is based on extensive research and my own experience with using and servicing the posts. 

Edited by Steady Spin
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why is top tube not an option?

 

Not sure if you're trolling.....

 

The technical answer though is that the carbon layup design used in the tubular bike sections and components (like handlebars and seat posts) isn't made to resist much stress in "clamping". So they're super strong in bending and tension/compression, but you can easily crack a carbon seatpost just by over tightening the clamp bolt with a normal allen key. Clamping the top tube is the same. You can ride off huge drops and the frame will be fine cos it's designed for those forces, but then slightly overtightening your work stand clamp can crack the frame.  

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Difference is that the force from the 100kg rider is supported by hydraulic oil in a presumably aluminium chamber. The 12kg pull is potentially supported by a rubber seal. Tension and compression aren't the same when it comes to these hydraulics 

 

Glad to hear that you haven't had any issues though

 

 

what 12kg pull? I would not advocate that the dropper be clamped in any way other than the post fully extended. 

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what 12kg pull? I would not advocate that the dropper be clamped in any way other than the post fully extended. 

 

Bike weight supported by the fully extended post. 

 

Sorry, wasn't 100% clear. I assumed that not clamping a collapsed post would be more obvious.

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