seatpost damage

open topic, for anything cycling related.

seatpost damage

Postby scott w » Thu Jan 24, 2013 11:31 pm

hi everyone , i have a felt f3 , and noticed a mark on my seat post ( carbonfibre) it looks like the clamp has left a small impression in the seatpost .
the seat post clamp has maximum 5nm on the top bolt and 7nm on lower bolt which i did up to 4nm and 6nm respectively , the mark is only were the split in the clamp is , i use a tension wrench .
i had a slight creak a little while back so removed the seatpost to apply some carbon paste and noticed the mark , i have since bought a deda seatpost and dont want to have it happen again .
i have fitted it tonight and have only tightened the bolts to 2.5nm with paste , i havent taken it for a ride , what is the minimum bolt tesion people have used with no seat post slippage .
has anyone else had simular issue .

cheers scott
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by BNA » Fri Jan 25, 2013 8:10 am

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Re: seatpost damage

Postby biker jk » Fri Jan 25, 2013 8:10 am

2.5 NM sounds too low to stop the post slipping. Using carbon paste allows you to use around 30% less torque, so on a 5 NM post I would go to 3.5 NM.
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Re: seatpost damage

Postby scott w » Fri Jan 25, 2013 8:43 am

The mark is deep worry me enough to get a new seatpost after seeing the thread on here about the poor bugger that had his post break and cut him up .
On the clamp it has the maximum is 5nm on the top and 7nm on the lower bolt , i being aware of this only did them up to 4nm and 6nm on the old seatpost .
The mark seems to be were the split is on the clamp as if the edge is cutting in to it , could be from the post rocking in the clamp .
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Re: seatpost damage

Postby RonK » Fri Jan 25, 2013 9:01 am

scott w wrote:The mark seems to be were the split is on the clamp as if the edge is cutting in to it , could be from the post rocking in the clamp .

So you have bought a new post, but could the clamp be the cause? Is it clamping hard on the post instead of the mast? Do Deda have a matching clamp?
I'd be sticking to the recommended torque. CF assembly compound will make a mess of the post if it slips.
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Re: seatpost damage

Postby Howzat » Fri Jan 25, 2013 10:39 am

scott w wrote:The mark is deep worry me enough to get a new seatpost after seeing the thread on here about the poor bugger that had his post break and cut him up .


In Skull's case, it was a metal bolt in the seat clamp that sheared, not the seatpost per se. Can you post a picture of the damaged seatpost?

Could it be possible be that under-tightening of the bolts lead to seatpost movement, which caused the mark?
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Re: seatpost damage

Postby HLC » Fri Jan 25, 2013 1:51 pm

Howzat wrote:
In Skull's case, it was a metal bolt in the seat clamp that sheared, not the seatpost per se. Can you post a picture of the damaged seatpost?

Could it be possible be that under-tightening of the bolts lead to seatpost movement, which caused the mark?


This is my thoughts.

Tighten it to 4 & 7 respectively and leave it.
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Re: seatpost damage

Postby scott w » Fri Jan 25, 2013 6:38 pm

The post never slipped , i only found it when i removed it as it had a creak coming from the post , it was tensioned to 4nm on the top and 6nm on the lower bolt , it does look to me like it may have been flexing in the top portion of the clamp .
The max tension on the top bolt is 5nm so i thought 4 would be fine with paste .
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Re: seatpost damage

Postby Derny Driver » Fri Jan 25, 2013 8:55 pm

One of my mates carbon seatpost snapped as he was riding along at 28kph on a flat hotmix road, and he fell backwards and landed on his head. That was actually lucky because a few minutes earlier he had made a 90kph descent on our nastiest mountain ... a crash there would have killed him. The seatpost had been adjusted by a bike shop the week before, it was obviously overtensioned.
Ive also seen some nasty crashes caused by snapped stems and stem bolts. Cycling is risky enough without having this sort of equipment failure.
For myself (my son's bikes), I have 2 rules:
1. Aluminium seatposts only.
2. Aluminium stems only with 4 titanium bolts, never 2.
I'll put up with the extra 8.3 milligrams of weight to make sure these preventable accidents dont happen.
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Re: seatpost damage

Postby RonK » Fri Jan 25, 2013 9:34 pm

Derny Driver wrote:I have 2 rules:
1. Aluminium seatposts only.
2. Aluminium stems only with 4 titanium bolts, never 2.

I'm not sure what you hope to achieve with these rules. It's not at all uncommon for alloy stems, seat posts and handlebars to fail.
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