saddlebag on carbon seatpost

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webber
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saddlebag on carbon seatpost

Postby webber » 14 Oct 2018, 5:39pm

ive just picked up a bike with a carbon seatpost that I would like to fit my bridge street saddle bag https://road.cc/content/review/123753-b ... bag-medium but is it safe to clamp to a carbon seatpost???

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Paulatic
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Re: saddlebag on carbon seatpost

Postby Paulatic » 14 Oct 2018, 6:43pm

The seat post is clamped at the top of the seat tube. Why not clamp it further up too?
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webber
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Re: saddlebag on carbon seatpost

Postby webber » 14 Oct 2018, 7:29pm

Paulatic wrote:The seat post is clamped at the top of the seat tube. Why not clamp it further up too?

im sure i was told that you shouldnt camp anything to a carbon post but i make you right

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Paulatic
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Re: saddlebag on carbon seatpost

Postby Paulatic » 14 Oct 2018, 8:41pm

I’ve read all sorts of nay sayers reports on carbon fibre. When I bought a bike with a carbon seat post I asked the shop if I could clamp my carradice sqr to it. They couldn’t see there would be a problem. I was wary but I have done it with care of course.
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pwa
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Re: saddlebag on carbon seatpost

Postby pwa » 14 Oct 2018, 9:04pm

Paulatic wrote:I’ve read all sorts of nay sayers reports on carbon fibre. When I bought a bike with a carbon seat post I asked the shop if I could clamp my carradice sqr to it. They couldn’t see there would be a problem. I was wary but I have done it with care of course.

On the other hand I would be cautious about attaching anything to seatposts, of any material, that are particularly light. I've broken a lightweight alloy post when using an SQR Carradice bag, and a ten mile journey over several hills to get back to my car, with no saddle, didn't half have my thighs burning. :lol:

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foxyrider
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Re: saddlebag on carbon seatpost

Postby foxyrider » 14 Oct 2018, 9:51pm

I certainly wouldn't clamp anything around a CF seatpost, especially anything where there will be a load at the interface. The potential for crush damage is perhaps not so great but cantilever weight may well cause premature and catastrophic failure.

Personally I don't trust CF for seatpost or stems - if I want light I use Ti (which I am quite happy to clamp stuff to).
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webber
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Re: saddlebag on carbon seatpost

Postby webber » 15 Oct 2018, 7:30am

thanks for the replys so I can but shouldn't then :lol: :lol:

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Mick F
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Re: saddlebag on carbon seatpost

Postby Mick F » 15 Oct 2018, 8:10am

I had a carbon seat post on my Moulton.
I sold the carbon one and bought an alu one and made a profit on the deal.

Not only a profit, but all the issues with carbon have gone, and the alu post was a whole 19g heavier! :lol: :lol:
Mick F. Cornwall

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Paulatic
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Re: saddlebag on carbon seatpost

Postby Paulatic » 15 Oct 2018, 8:28am

webber wrote:thanks for the replys so I can but shouldn't then :lol: :lol:

You are now armed with information you can make your own mind up. I should add I only had my sqr on for a few weeks and had the post sleeved with an old inner tube.
I’ve just took a look at your bag linked..... :( viewtopic.php?f=1&t=125530&p=1280904&hilit=Bridge+street#p1280904 You’ll be lucky :D
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webber
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Re: saddlebag on carbon seatpost

Postby webber » 15 Oct 2018, 9:50am

Paulatic wrote:
webber wrote:thanks for the replys so I can but shouldn't then :lol: :lol:

You are now armed with information you can make your own mind up. I should add I only had my sqr on for a few weeks and had the post sleeved with an old inner tube.
I’ve just took a look at your bag linked..... :( viewtopic.php?f=1&t=125530&p=1280904&hilit=Bridge+street#p1280904 You’ll be lucky :D

i might just get an alloy post but don't know ive got a carradice super c saddlepack which will do most of the time might even get a super c audax and bagman but have heard of them snapping seat rails

Brucey
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Re: saddlebag on carbon seatpost

Postby Brucey » 15 Oct 2018, 10:23am

believe it or not, not all CF is the same. Quite a lot of 'CF seat pins' are made by wrapping CF around an aluminium post. They are not especially light and much of the strength may come from the aluminium not the CF. Others are all CF, but the CF is of poor quality. Such seat pins may break anyway and a saddlebag may just give them the final nudge...

Seat pins only don't slip because they are a snug fit over a length, and the binder is nipped up. If the seat pin is inserted only a short way into a frame, it doesn't matter how tight the clamp is or what the seat pin is made of; it'll move, and it'll move more easily with some seat pins than others. Same goes for anything clamped round a seat post too.

Clamping to seat pins to support a saddlebag is inviting trouble if the seat pin is light-built and/or the saddlebag is heavy and/or the clamp is tight.

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webber
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Re: saddlebag on carbon seatpost

Postby webber » 15 Oct 2018, 1:50pm

Brucey wrote:believe it or not, not all CF is the same. Quite a lot of 'CF seat pins' are made by wrapping CF around an aluminium post. They are not especially light and much of the strength may come from the aluminium not the CF. Others are all CF, but the CF is of poor quality. Such seat pins may break anyway and a saddlebag may just give them the final nudge...

Seat pins only don't slip because they are a snug fit over a length, and the binder is nipped up. If the seat pin is inserted only a short way into a frame, it doesn't matter how tight the clamp is or what the seat pin is made of; it'll move, and it'll move more easily with some seat pins than others. Same goes for anything clamped round a seat post too.

Clamping to seat pins to support a saddlebag is inviting trouble if the seat pin is light-built and/or the saddlebag is heavy and/or the clamp is tight.

cheers

so saddlebag and bagman is best the??

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Chris Jeggo
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Re: saddlebag on carbon seatpost

Postby Chris Jeggo » 15 Oct 2018, 2:15pm

In one image you link to
Bridge Street Saddlebag - seat post clamp.jpg

the seat pillar appears to be a saddle cradle insert fixed in a plain tube. In this case, if the insert is a good fit and goes further down the tube (by a distance of several tube wall thicknesses) than the whole of the bag support clamp, then it is probably all OK.
Or, to put it another way, if using the bag support loads the seat pillar in much the same way as fixing the saddlebag direct to the back of the saddle then the situation is fairly easy to evaluate.
Otherwise, think about it very carefully.

pwa
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Re: saddlebag on carbon seatpost

Postby pwa » 15 Oct 2018, 3:32pm

Paulatic wrote:
webber wrote:thanks for the replys so I can but shouldn't then :lol: :lol:

You are now armed with information you can make your own mind up. I should add I only had my sqr on for a few weeks and had the post sleeved with an old inner tube.
I’ve just took a look at your bag linked..... :( viewtopic.php?f=1&t=125530&p=1280904&hilit=Bridge+street#p1280904 You’ll be lucky :D

Yes, if you do it you are very naughty, but do protect the surface of the post with a wrap of something to avoid scratching.

althebike
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Re: saddlebag on carbon seatpost

Postby althebike » 15 Oct 2018, 3:49pm

When I was looking for a bag, for my carbon SP I was met with a sharp intake of breath with any metal clamping, and so I brought an alpkit that uses velcro, I have been told this is fine, the proof is in the pudding of course, if a prev.poster broke an alloy post, maybe it is not the material that is the key issue.