Carbon seat post slipping into frame

[tudor_77]

Hi guys,

I bought a Giant Defy Composite 2 a few days ago to replace my old Boardman. However, after a couple of rides I realised that the saddle had crept down into the frame by about an inch or so. I do not own a torque wrench (Carbon seatpost and Frame) and could not take it back to the store as it was only noticed Saturday night.

Anyway, I took part in an event (50 miler) this morning and had one of the bike mechanics take a look and he said the screws were way too loose and re-tightened them to the correct torque. This seemed to solve the problem for the first 25 miles or so but then the post started to slip back down into the frame again (making the last 20 miles extremely difficult).

At first I thought that I would probably need to put some of that carbon fibre paste stuff on the post to make it stick, however I gave the screws on the seatpost clap a quick test when I got home and sure enough they are loose again.

I'm guessing the vibration from the road is making the screws loosen over time, not good on a carbon fibre frame where a sudden drop could damage the frame beyond repair.

Should the screws be able to just loosen themselves like that, even after they are tightened to the correct torque? Do all carbon bikes do this? Also, has anyone had this issue before and if so, how did you get it resolved?

Cheers.

 

[Smokin Joe]

Buy a new clamp, guaranteed to solve the problem - which is a nughty thread either on the clamp or the bolt.

 

[MikeW-71]

Should the screws be able to just loosen themselves like that, even after they are tightened to the correct torque? Do all carbon bikes do this? Also, has anyone had this issue before and if so, how did you get it resolved?

It'll be the same clamp as my Defy Advanced 2 uses. With the correct torque and carbon paste applied, my seatpost has never slipped and the screws have not loosened with riding. Possibly a drop of blue threadlock will stop them vibrating loose, or there's a bad thread and they may replace the clamp and screws. Pop it back to see the mechanics.

 

[Cuchilo]

Mine slipped when I first bought the bike . Hasn't done since but I have been tweaking things a lot so for the first six months of ownership the bolts go tightened a fair bit .

 

[tudor_77]

Okay cheers guys, never owned a carbon bike before so was unsure about all this. The guy in the shop pointed out to me that the Defy Comp has like a cut out in the frame on the seat tube so if the stem suddenly slipped all the way down it could crack the frame! This has got me more than a little paranoid haha.

Will pop it back to them today and see what happens. Really loving the bike so far though, I can see why people rave about carbon frames.

As always, thanks for the advice

 

[Brava210]

Hi guys,

I bought a Giant Defy Composite 2 a few days ago to replace my old Boardman. However, after a couple of rides I realised that the saddle had crept down into the frame by about an inch or so. I do not own a torque wrench (Carbon seatpost and Frame) and could not take it back to the store as it was only noticed Saturday night.

Anyway, I took part in an event (50 miler) this morning and had one of the bike mechanics take a look and he said the screws were way too loose and re-tightened them to the correct torque. This seemed to solve the problem for the first 25 miles or so but then the post started to slip back down into the frame again (making the last 20 miles extremely difficult).

At first I thought that I would probably need to put some of that carbon fibre paste stuff on the post to make it stick, however I gave the screws on the seatpost clap a quick test when I got home and sure enough they are loose again.

I'm guessing the vibration from the road is making the screws loosen over time, not good on a carbon fibre frame where a sudden drop could damage the frame beyond repair.

Should the screws be able to just loosen themselves like that, even after they are tightened to the correct torque? Do all carbon bikes do this? Also, has anyone had this issue before and if so, how did you get it resolved?

Cheers.

Why not take it back?

 

[tudor_77]

Hi Brava,

Yes as stated above I am popping it back into them tomorrow. I just wondered if this was a normal thing to expect from a carbon bike (all my previous ones were aluminium) or if it was something to be overly concerned about. There is plenty of information online about posts slipping due to a lack of paster or incorrect torque but could not find much on bolts in the seat post clamp working their way loose over time.

 

[Brava210]

My bike is carbon a boardman Pro with no problem.
Although I also have a Mekk Carbon which does suffer the seat post slipping down.
Not sure why yet, probably going back to wiggle

 

[themosquitoking]

Hi Brava,

Yes as stated above I am popping it back into them tomorrow. I just wondered if this was a normal thing to expect from a carbon bike (all my previous ones were aluminium) or if it was something to be overly concerned about. There is plenty of information online about posts slipping due to a lack of paster or incorrect torque but could not find much on bolts in the seat post clamp working their way loose over time.

I wouldn't say a 25 mile ride is "over time" it's more or less instantly.

 

[Deleted member 18052]

Get some finish line fibre grip on it and then torque the bolts correctly. Mines not moved since

Daz

 

[tudor_77]

I wouldn't say a 25 mile ride is "over time" it's more or less instantly.

You're right man and very worrying too. Probably a threaded screw or clamp I think. There is already some carbon paste on the stem and the bolts have been torqued correctly on two separate occasions. Will find out tomorrow when I take it in.

 

[themosquitoking]

You're right man and very worrying too. Probably a threaded screw or clamp I think. There is already some carbon paste on the stem and the bolts have been torqued correctly on two separate occasions. Will find out tomorrow when I take it in.

Threaded bolts or maybe a crack in the seatpost clamp possibly it doesn't hold the seatpost firmly enough even when tightened and the extra vibration allows the bolts to work loose.

 

[tudor_77]

Just a quick update. Took the bike into the guys at Giant and whilst there was nothing visibly wrong with the clamp they replaced it anyway. As a result the seat post has stayed put and not crept back down. Such a relief!

So I guess if anyone ever has a similar problem it may be more than just needing to apply some fibre paste and set the correct torque, which would be the usual assumption. Sometimes it can just be down to a wayward component!

Anyways, thanks for the help and advice guys. Hopefully this thread can help someone with similar problems one day!

Cheers

 

[MikeW-71]

Excellent

 

[02GF74]

carbon frames usually have an aluminium insert at the top of the seat tube; the issue here is the carbon post; carbon is softer than Al so you need to be careful on how much you tighten the clamp, too much and you risk damage the seat post.

some lightweight clamps are quite bad in holding a seatpost. carbon paste and tightening the clamp bolt fixes that.