Mild seat post panic

slogfester · Post by **slogfester** » 21 Feb 2014 16:43

Mild panic this afternoon. I have been suffering from a slipping carbon seat post (Deda Superzero) in my titanium frame. Applied some carbon paste to increase friction, but still slipping a little. I feel it in my knees first and cant climb as fast!
When I adjusted and re-tightened today I heard that sickening cracking sound despite using a torque wrench

Closer inspection (see pic) shows that the carbon has, at best, folded or just simply failed? I have had carbon seat posts before and not suffered this. When I ran my hand over it I got a nasty carbon splinter. Over tightened and/or carbon weave too soft? I only tightened to manufacturers recommended torque.
Don't trust it, so swapped (back) to a Ti seat post from my tourer. Trouble is, the set back is not enough on the Ti post and I really like the added flex that the carbon gave. (I am only using half the length).
Advice please

20140221_160856 by Slogfester, on Flickr

Grogz · Post by **Grogz** » 22 Feb 2014 20:44

To get that impression in the post, it looks as though it was a bit tight, Barry! How's the calibration on your torque wrench? It's always worried me that their accuracy deteriorates and could end up with a costly break like this. Otherwise, it's possible that the carbon was not perfect - may be worth getting an independent opinion.

AlanW · Post by **AlanW** » 22 Feb 2014 21:06

We had a conversation about this today at the Upton control and I think that we "may" have found what the problem was.

slogfester · Post by **slogfester** » 23 Feb 2014 17:41

Alan had hypothesised that I may have purchased a slightly under sized seat post. Quite feasible given my lack of technical finesse. But I have double checked and both seat post and inside tube diameter are 27.2 mm.
Torque wrench is calibrated and I have never over tightened anything else before; I'm very cautious.

dweben · Post by **dweben** » 23 Feb 2014 19:05

Odd distance between the top and the bottom of the pattern. Not the size of a clamp, but more the size of a shim or something. Was that bit inside the tube, or above where a bike shop clamp would go?

Post by **CakeStop** » 23 Feb 2014 19:13

What was you torquing it to Barry?

slogfester · Post by **slogfester** » 23 Feb 2014 19:55

Paul- its like that because seatpost was slipping and it has been clamped in various positions
Steve- 8 nm max, but I usually stop at 5 nm.

Post by **CakeStop** » 23 Feb 2014 21:15

I saw a post on another forum from someone who broke one of those seatposts at 5nm and then experimented with the remainder and found it failed at anything over 4nm

Are you using an offset (asymmetrical) clamp?

slogfester · Post by **slogfester** » 24 Feb 2014 14:15

Steve- yes, I am using a asymmetrical seat post clamp

Post by **CakeStop** » 24 Feb 2014 17:04

Found it - 2nd page of customer reviews on wiggle

slogfester · Post by **slogfester** » 24 Feb 2014 23:05

Thx Steve, I see it too.
I purchased via probikekit. I'll try my luck with a warranty claim.
It DID feel great (lots of the right sort of flex), but I doubt I'll be able to pluck up enough courage to fork out for another one.
As well as carbon paste I think I have read that you can use some sort of tape to help stop slipping?

Patch · Post by **Patch** » 26 Feb 2014 07:44

I see this quite a lot. Alan is sort of right. The top of your seat tube/clamp is pinching inwards and squeezing the seat post. It's a case of tolerances being at the loose end so although seatpost is right size it's still pinching just a bit. I suspect whatever carbon seatpost you put in here the same will happen again.

slogfester · Post by **slogfester** » 20 Mar 2014 17:34

Probikekit/Deda have accepted my warranty claim. Would like a replacement carbon seatpost (I like the flex) but mindful of Chris' comment.
Try and squeeze a shim thinghy in there? And/or a beefier carbon seatpost? Recommendations please with 20-25 mm set back.
Or throw the towel in and go Ti?
thanks

Patch · Post by **Patch** » 20 Mar 2014 18:28

If their doing it under warranty then it's not costing. Just get another one and be careful how you tighten it up. Use proper carbon grip when you put it in and no more than 4nm. Sometimes carbon posts slip at the proper torque when people use ordinary grease so they end up tightening it more

Also make sure the inside of the frame is smooth. Some frames have quite sharp edges where it clamps, this is far more common than you may think. If you think it is a bit sharp I would suggest showing it to someone who has experience of this and show them the picture of the old seatpost. They will be able to asses best action. I wouldn't just attack your nice titanium frame with a file. Despite my earlier pessimism it is likely that the new seatpost won't be at the loose end of the tolerance. On the other hand I think this idea that carbon posts are more comfortable than alloy is a bit of a myth anyway invented by those who want to sell you a carbon seatpost. Diameter of the post is a much bigger factor. Big fat alloy seatposts are a bit harsh skinny 27.2 ones are fine.

Philip Whiteman · Post by **Philip Whiteman** » 20 Mar 2014 19:49

Interesting point about grease. I realised the grease will naturally cause slippage of a carbon post and have therefore never used it. However, 'carbon grip' is a new one on me. So thanks for the advise, Chris.

http://www.wiggle.co.uk/finish-line-fib ... -gel-50ml/

AlanW · Post by **AlanW** » 20 Mar 2014 20:13

I have always used Ritchey Liquid Torque. However it is becoming very difficult to source in the UK now for what ever reason?

Patch · Post by **Patch** » 21 Mar 2014 08:03

That's exactly the stuff we use Phil.

George · Post by **George** » 21 Mar 2014 10:01

I had something similar happen last summer. My guess was the same as Patch's: excessive tolerance in the manufacture of post and/or frame leading to a loose fit, followed by compensatory over-tightening by me.

I like carbon as a frame material, but my seatpost experience, combined with the many other similar incidents I've read about, now make me dubious about carbon components such as posts and stems. They aren't generally lighter than good alloy alternatives, the bike doesn't 'feel' any different, and the risk of catastrophic failure seems to be significantly greater.

Pedlo Mudguardo · Post by **Pedlo Mudguardo** » 21 Mar 2014 11:32

I also had a simular problem with a Ritchey carbon seatpost which developed a 30mm split hidden inside the frame. This is something I happened to notice the day before last summer's 219 mile ride to Weston....

To cut to the point I decided to stop messing around and fit a Thomson Elite alloy post which besides being beautiful is stiff (in a good way) and much lighter than my original carbon post.

Patch · Post by **Patch** » 21 Mar 2014 20:32

I'll echo that Thomson seatposts are the business.