Hello,

My carbon post slips down in my carbon frame over the course of a ride. Quite annoying.

I have assembly paste, and have changed the QR (Which helped, but didn’t solve).

I noticed on my mates bike (which is steel frame & alu post) when I went to lower the saddle I had to use pretty much all my arm muscle to close the QR – he had it suuuuuper tight.

You can close my QR with just thumb and index finger pretty much.

Now I understand his frame & post are different materials to mine, but could I afford to tighten my QR slightly tighter? Could anyone describe how much effort they require to close their QR on their carbon/carbon setup?

I don’t have access to any torque wrench unfortunately. The frame is a C456.

Cheers!

also: in b4 “tighten it till it cracks, then back off a touch”

Get a seat clamp and a torque wrench :O)
Much easier.
I guess you move you saddle height a lot or transport your bike in the car hence the QR?

Carbon seat tubes and carbon seat posts are designed to be clamped and should be very strong, it sounds like you can do it up a fair bit tighter than you have

I’ve got a C456 but with a Reverb.

I’ve also got a carbon seatpost on my alu road bike.

On both of them I’ve never had any slipping problems. I bought myself a ‘preset’ torque wrench a while ago and it turned out both seatclamps were below the recommended torque, despite me thinking that they were ‘about right’. So you’ve probably got plenty of margin to up the torque without breaking anything.

Unless you weigh 30 stone and have got an undersized seatpost, of course.

A decent quality seat clamp and torque wrench and learn to ride with your saddle in one position otherwise you will cause a failure of either your post or frame at some point if you continue to raise/lower your current set-up using a QR.

A QR is not recommended for such a combination and if the worst did happen and your frame cracks i doubt On-One would honour any warranty and quite rightly, it’d be down to user error i’m afraid.

Surely, the seat tube ‘slit’ that allows the frame to grip the seat post when you close the QR can only flex to the point where the seat tube matches the diameter of the seatpost, unless you are deforming the seatpost as well (you’d have to try quite hard to do that)….

I’d have thought unless there was a design/manufacturing issue or you were being particularly ham-fisted you would struggle to damage the frame and/or seatpost through over-tightening.
FWIW, I’ve got an alu seatpost in my carbon Stumpjumper FSR and use my palm to close the QR. It’s takes a fair amount of force & nothing has exploded yet…..(reminder to check seat tube for cracks this evening)
🙂

EDIT: as per bails’ comment. Make sure your seatpost is the correct size too!!

aye yeah seat post is defo correct size 🙂 but thanks for the replies.

I might tighten it up a bit more. I think a little tighter and the slipping issues will stop.

Yeh i put it down occasionally to get in cars and vans. I don’t touch it at all when riding, other than to put it back up from the slippage!

Get some Fiber Grip from Finish Line if you’re worried, you shouldn’t need to clamp so hard.

Rather than a full blown torque wrench, check the frame handbook and find the force for the seatpost clamp, if its 5Nm then ditch the QR, get a clamp and get this

Before you tighten it up any more check to see if there is a max insertion mark on the post, I made this mistake a while ago.

Since I’m a bit of a short arse I don’t have much post showing, bought a nice new carbon seat post for the road bike, popped it in and decided to drop it a little mid ride. I didn’t realise at the time that I’d gone about 5mm past the max insertion line, tightened up the clamp and CRACK. Bugger.

On closer inspection there was a max insertion line, outside of which the post wall got thinner or wasn’t reinforced. A torque wrench wouldn’t have saved me there.

I managed to put nearly 20Nm into a carbon frame + seatpost thanks to a dodgy torque wrench/idiot operator (the little mode switch on it hadn’t fully engaged so was half in torque wrench mode and half it conventional mode), I got suspicious it was taking way more force than it should and realised what had happened (I checked what it had got up to before backing it off :p ). I’m not recommending you do it that tight (my frame is labelled for 5Nm seatpost clamping) but it’s still working fine 2 years later and no cracks appeared.

+1 to Bail’s comemnt, buy one of those pre-set torque keys and learn what 5Nm (or what ever your rating is) feels like.

I too was way under the limit when I used a normal Allen key realised I could do it up much tighter.