Chombi

After a years of searching, I finally found a quill type Stronglight Delta seatpost to almost complete my Stronglight Delta group (just missing a Delta BB at this point) that is now installed on one of my CF framed bikes.
My reason for planning to use such would be to relieve some pressure on the aluminum lug seatpost clamp on the bike that has been known to crack on these bikes if over-tightened............. But now I'm not sure how a quill wedge might affect the CF frame seat tube. I know quill stems have been known to crack aluminum steerer tubes if one is not careful with tightening them, but would CF be more resistant to such?
Anyone here ever use a quill stem on a CF tubed frame before and care to share if it worked out?

RobbieTunes

I would assume it goes down lower than the lugs, so I just don't know.
After seeing what star nuts do to carbon steer tubes, not sure what I'd do.
The wedge is probably safer than the cone, but I'd make sure there's not a lot of play.
Just seems like a lot of weight to leverage against the side of a carbon tube.
If there was room to slide it inside a shim or sleeve, maybe.
I'd hate to see anything happen to the Line Seeker.

CliffordK

Let's experiment on YOUR bike.

Hmm, CF should take both compression and tension. But, you can get quite a bit of force with those quills in a part of the frame that wasn't specifically designed to take it. Although, it should be able to withstand some internal leverage on the seatpost.

I don't think I'd do it.

Chombi

Yes, it is a wedge type quill on the seatpost and the quill wedge will be surely below the aluminum seat lug. I also thought about a reinforcing tube shim, but I'm sure there's just no space for such.
The Delta seatpost is destined to go on my Peugeot PY10FC. The Line Seeker is actually good with it's proprietary, machined down, 21mm Campy NR seatpost and steel lug/clamp
The Peugeot has a lot of Vitus "DNA", so I was thinking it could be OK as Vitus did sell quill type seatpost for their bikes. Thing is, they used a a type of quill that was more similar to the Atax cone type 3 piece design that seems to distribute the pressure on the seat tube more evenly by having concentric cuts to the "wedging tube", instead of just the typical vertical.

RobbieTunes

I trust your judgement, and you are a much smarter wrench than I.

kunsunoke 

As nice as it probably is, the quill seatpost will in no way compensate for an under-built seat-clamp area. Given what we know about carbon fiber, the post might cause a bulge (opposite of a crush) in the seat tube, where the expander bolt wedges against the inside of the tube.

Carbon is directional, crush sensitive, and unforgiving. If it were my bike I wouldn't risk it. Ship it to Calfee for repair when/if the clamp area breaks.

jyl

That is pretty thick CF tubing, if I recall. And the quill will be sharing the clamping duties with the seat lug clamp, rather than trying to do it alone. I would try it. Use your micrometer to check if the carbon tube is bulging at all when you tighten the quill and periodically thereafter.

randyjawa 

The answer, in my mind, depends on what bicycle the post is being installed in. If the tube set is thin gauge tubing, then the answer is a resounding NO.

A wedge offers an incredibly powerful mechanical advantage. I would not want to give-er-a-try, just to see if the tubing bulges. And that bulge, if it did form, might not do so just during installation. The potential for damage (to the tubing) is presented when in use, also. So...

I would not do it and, if those seat posts were of much value, the design would still be in use today. Perhaps my reasoning is flawed, but I don't see many high end bikes (then or now), be they steel, aluminum or carbon fiber, fitted with an expander inside their tubes.

CliffordK

I like the idea of using both quill and seatpost clamp.

I'm not sure how much slop there is with the seatpost in the tube. Most are fairly tight, but the quill would keep it from moving at the bottom which might be good.

Now, I suppose one question is, say there is some natural flex in the seat tube and the seatpost. Then, if they flex separately, then having 2 points of attachment could be very bad.

Lascauxcaveman 

As much as I worry about the strength of vintage alloy seat post clamps, I seriously doubt CF tubes were ever meant to be stressed in that direction. My guess is it will break before it's torqued down tight enough to help hold the seat post in place much.

Chombi

After thinking about this with all the good input (thanks very much guys!) in this thread in mind, I think:
1) Tightening the wedge as much as one would do on a steel bike will most likely be a bad idea with a CF frame.
2) there must be some load that the CF tube CAN take but less than Al and Fe frame tubes
3) I still don't understand how CF might react to a point load from the edges of the quill wedge, but hearing about how thinner CF on modern bikes can sometime get easily damaged by such (as owners sometimes found out when they just drop their bikes against hard pointed things in our environment) means CF will not tolerate as much such point loads as Fe and Al frame tubes.
4) I think any stabilizing effect that a quill wedge might contribute might help keep the Al seat lug clamp from cracking in the future.
5) I think I can use the quill post on the bike, but just not tighten the quill that much, just enough to get some grip on the seat tube but split the seat post anchoring duties with the seat lug clamp by maybe about 20% at most. Hope I can dial this all in by feel.
6) I think that this Stronglight Delta post was designed and made at a time when manufacturers that made bikes with 25mm (which this post's size is) seatpost requirements like Vitus and ALAN was mostly producing Al frames, so even back then, they must have had no real idea if the seatpost would work on their early CF frames as just the only means of anchoring a seatpost to a CF frame.
7) In the end, I can also just use the post without the quill wedge and bolt installed, to mostly complete the Stronglight Delta group on the bike, and save a bit of weight in the process....but that will be a fall back position if things dend up not feeling right with the quill wedge.

miamijim

I'd use a slightly oversized post with the lug clamp before I'd use an expanding post in carbon.

lord_athlon

I'd get the longest 25mm post I could find.

plonz 

I have both a quill seat post and a carbon bike and never shall the two meet! I wouldn't do it. I would put my focus on proper installation of a normal seatpost. By the right size, use carbon assembly compound (the stuff with grit in it) and you should be able to get it plenty snug on the low end of the torque specification. Hopefully your frame that is prone to breaking only does so when over tightening. Park tool sells the compound.

LdP

First of all, Thanks for all valuable information in this forum!
Could I ask for and update on Chombi's idea? I'm also considering the expanding seatpost solution, as
I finally found and bought a beautiful py10fc for a low price... But with a hairline crack around the drive side of the seatpost clamp lug thinking it could be fixable. I already exchanged emails with Vitus knowledgable repair authority Guywires and he said it isn't repairable. Just to J-B weld and to bond the seatpost with epoxy at the desired height from inside.
If the expanding seatpost idea worked, it could save me from the evilly-friendly epoxy!