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Repair stand - clamping on carbon seat post on

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Repair stand - clamping on carbon seat post on

Old 08-31-15, 06:35 PM
  #1  
Redbullet
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Repair stand - clamping on carbon seat post

Hello,

I canít decide how to clamp a carbon road bike on a repair stand Ė Iíve seen too many opinions here and there. Grateful if somebody can advise; briefly, it looks as follows:

-Clamping on top tube is excluded: TT has a rectangular profile with rounded edges and with variable section. Furthermore, if you strongly press the top tube between your fingers, it slightly deforms (I wonder how does it manage to carry my weight of 80 kg, but thatís another story).
-The only alternative I see is clamping on the seat post. It has a cylindrical shape and it appears to be strong, butÖ it is carbon fiber. I donít want to change it with another one only for clamping Ė the whole carbon fiber environment doesnít look reliable for repetitive mounting and dismounting.
-The shape of the stand clamp is very similar with this one (please select the picture of the clamp):
One Bike Workstand - | Decathlon
-The seat post is this one (or very similar):
Ritchey WCS Carbon LINK Flexlogic 15mm Offset Seatpost

The questions are:
-Should I clamp on the seat post? Note that the clamp of the stand is not round and it would press the seat post on 4 areas at 90 degrees.
-Would the seat post support the forces if I the bike is horizontal, or should I let the clamp support to rotate free (the bike would be finally tilted with the front wheel down)?
-How should I find what is the safe force for clamping?

Thanks in advance
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Old 08-31-15, 06:40 PM
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CACycling
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The best way is to get an alloy seat post of the proper diameter and swap it for the CF one when you need to clamp it in the repair stand.
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Old 08-31-15, 06:59 PM
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That post is 100% fine to clamp too.

A seat collar puts far more pressure on a post over a much smaller area. A repair stand puts far less pressure over wider area.

I've clamped many, many carbon posts. I would say no to an aero post since uniformity of thickness isn't always equal, but circular carbon like that Ritchey post are fine.

Last edited by Jamminatrix; 08-31-15 at 07:03 PM.
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Old 08-31-15, 07:53 PM
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I'm not sure about round CF seatposts...but I concur with Jammin WRT replacing it with a metal one for mounting does seem like the best option. For aero CF seatpost...that is a conundrum. When I got my new CF bike earlier this year and I took it in for its 100 mile free checkup...the wrench didn't clamp it at all. He simply put the nose of the seat in the clamp...and even then he only softly clamped it. I haven't had to do much beyond changing pedals to that bike yet. But I sure wish there was a better way to mount it on my workstand. For now, I just set it up in my stationary trainer to work on it.

Dan

Last edited by _ForceD_; 08-31-15 at 09:49 PM.
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Old 08-31-15, 08:09 PM
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I invested in this stand: https://www.amazon.com/gp/product/B00...rch_detailpage when I changed to a carbon bike. It seemed to me to be relatively cheap insurance.
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Old 08-31-15, 08:45 PM
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Didn't Park used to make some sort of substitute post that quickly adjusted to different diameters? Can't find it on the Park Tools site, but I'm sure I've seen it in the past.
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Old 08-31-15, 09:46 PM
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The Park tool goes inside a frame's ST and then places an outward force on the ST's walls. Not any better then a compressive force... If the ST isn't round at the depth that the tool's placement then it's even worse. Also the chance for the tool to not hold tightly (because of concerns of frame damage the tool often isn't tightened enough) the frame can slip down and off the tool.

I do agree that most round carbon seat posts can accept sufficient clamping forces to work on your bike with some basic care and common sense.

The best solution is to bite the bullet and accept that the cost of having some carbon frames and posts is that they don't play nice with your stand. Just because the bike is fancy and great during your ride doesn't make it easy to work on. Get a metal post, hang the bike with rope from a ceiling via the seat and bars, use a BB and drop out fixturing stand or use a cheap bike rack cross beam (like the Saris Bike Beam) and hang the bike with that. Andy.
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Old 09-01-15, 05:10 AM
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Thanks for the answers.
Using an Al seat post only for clamping looks best, however, the whole carbon fiber system does not look to me reliable enough to accept repetitive mounting - dismounting of the post, not to mention possible errors in tightening forces and the dirt that might accumulate between seat posts and seat tube.

So, I'll try to clamp on the carbon seat post. But there is one more question:
If the clamped bike is horizontally, there is a high flexing force applied by the clamp to the seat post, because the mass center of the bike is in front of the seat post, leading to pressing the bike front down. Would the seat post resist to that?

Alternatively, I could let the system rotate free after clamping the seat post - it will finally lay the bike some 45 degrees tilted to front. No more flexing force to the seat post, but working on the bike with the front tilted down is, obviously, not so comfortable.

So: horizontal and comfortable, or tilted down after clamping?
The bike weights around 8 kg or a little less.
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Old 09-01-15, 05:37 AM
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Originally Posted by Redbullet View Post
So, I'll try to clamp on the carbon seat post.
I think that's perfectly reasonable. You're limiting risk to just the carbon post. I'd be comfortable in doing that.

Alternatively, I could let the system rotate free after clamping the seat post - it will finally lay the bike some 45 degrees tilted to front.
I've the same issue w/my mountain bikes bikes. I do let them rotate forward somewhat. Not a full 45 degrees, but they aren't level either. Ironically, I'm not worried about the bike at all in that case, but rather about the stand.
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Old 09-01-15, 08:04 AM
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Just clamp on the seat post and don't worry about it. Seat posts are designed to resist compression, the clamp forces are spread over a much larger area than the collar, and the bike it relatively light weight. Most fully carbon bikes are <20 lbs, so it doesn't take a strong clamp to hold it. The seat post is design to resist the clamping forces of a 200 lbs rider hitting bumps in the road. The other main advantage of the seatpost is that if you do manage to crush it, its easily replaced.

Personally, I let the bike tilt forward about 35deg. It only looks awkward, its actually very easy to work on. The majority of the time you're working on either the rear drivetrain, which is rotated up making it easier to access, or the handlebars which are high enough to still be easily accessible. The only thing challenging is the front wheel, but if you're just working with the front wheel, you typically wouldn't even bother with a stand.
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Old 09-01-15, 10:57 AM
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Clamping carbon post to a stand is fine....as long as the post is completely vertically-mounted(no angle at all). This means the front wheel dips lower.....
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Old 09-01-15, 11:41 AM
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Clamp the post, but don't use any kind of cam thing to really vise down on it. It just needs to hold the bike relatively still.

That Park Tool seatpost substitute is a PITA. Yuk.
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Old 09-01-15, 04:28 PM
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Thanks for the answers.

I'll finally clamp gently on the carbon seat post as advised, but leaving the bike to hang free (front wheel will be lower) before fixing the clamp angle. I'll avoid the cam and manually use the nut only for tightening. Now I feel that the carbon seat post will have no problem with that.

After all, although the whole carbon bike appears to me as very delicate (I can slightly deform the top tube between my fingers), it still can carry me without any signs of failure. The carbon seat post looks as one of its strongest parts.
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Old 09-01-15, 04:51 PM
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Have owned carbon for many years and have always clamped to seat tube just under where it joins the top tube. If I buy into the fears of this forum, then my practice is an accident waiting to happen. My theory is the seat post reinforces the seat tube where I'm clamping, not allowing the tube to distort. Thoughts?
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Old 09-01-15, 04:55 PM
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Originally Posted by plonz View Post
My theory is the seat post reinforces the seat tube where I'm clamping, not allowing the tube to distort. Thoughts?
That's another theory that sounds very logical.
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Old 09-01-15, 06:45 PM
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Pretty much been throwing my bike on the stand (carbon round seatpost) after every ride for 2+ years. I do tend to let it rotate so center of gravity is under the clamp to reduce stress, though for actual work I rotate it as needed (to really get at it I pull the wheels and it is light enough I don't think it is under much stress).

What I don't do though is high torque things like pedals or crank arms. I haven't punched out a BB yet, but wouldn't do that with the bike held by seatpost either.

scott s.
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Old 09-01-15, 11:32 PM
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Originally Posted by Redbullet View Post
If the clamped bike is horizontally, there is a high flexing force applied by the clamp to the seat post, because the mass center of the bike is in front of the seat post, leading to pressing the bike front down. Would the seat post resist to that?
That is some of the same directional force the post undertakes supporting the weight of a rider, since seat tube angles aren't 90-degrees, but laid back.

If it can handle a 250lbs rider, there isn't much issue supporting a 20lbs bike.

Originally Posted by scott967 View Post
What I don't do though is high torque things like pedals or crank arms. I haven't punched out a BB yet, but wouldn't do that with the bike held by seatpost either
.
I agree for things like tightening/loosening pedals, you should take the bike off the stand; and that's generally for any bike, regardless of material.

You'll probably break the stand before the bike, especially cheaper ones.
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Old 09-02-15, 08:59 AM
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Originally Posted by plonz View Post
Have owned carbon for many years and have always clamped to seat tube just under where it joins the top tube.
I use this method when I clamp my wifes bike into the stand, her frame is AL, with a carbon seat post. The reason I do this is because of the frame size, and the amount of seat post available, and the size of my clamp, it's the best place to clamp for this bike. When I clamp it I can feel that the seatpost reenforces this area nicley, I can clamp with as much force as I want\need to hold the frame. If you have space and are worried about hurting your frame or seat post, this is a goo place to put the clamp. For my own CF bike and post, I just clamp the seat post.
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