How concerned should I be about this?

I’m thinking “very” but I wanted a second opinion.

Especially AJ’s opinion.

can you show me this tomorrow as pics can be misleading? - looks like a longitudinal crack though. I’ll be around in the AM. Best inspecting it out of the seat-tube as well where you can see the clamping surface.

Was this torqued to spec and did you use any assembly compound? It looks like the tube has slid a bit and shaved off some surface material.

Tube hasn’t slid, torqued to spec.

If the scratch goes deeper than the clear coat, I’d ditch it.

I second Mike’s take on that. If this crack is in the clear coat only, it’s probably fine; if, however, the crack goes through the carbon fibres, it will prgress untill it buckles. You really do not want to sit on it when that happens. Either way, I’d strongly suggest getting a new one (often it’s hard to determin how deep the crack goes). If it has been torqued to spec and you haven’t crashed, I’d try getting my money back form the store.

no need to torque to spec. i usually just tighten until i hear a slight cracking sound and then back off about a half turn.

thats a joke right? :stuck_out_tongue:

So, yeah … after I saw the picture of your seat post, John, I checked mine today just before the ride. Guess what: mine had an even worse and transverse crack just above the collar (not longitudinal as yours). Living up to my own suggestion, I thought about getting a new post myself, yet I didn’t have enough time to go to the store before the ride and was pretty sure if I was cautious about not running into too may pot-/sinkholes the it would probably survive another ride. Long story short, I was mistaken. Half way through the seat post fractured in the compression zone in the back and I was left with a wobbly, floppy seat and had to ride all the way back standing … my thighs hurt a bit now :wink:
So, John, get a new one soon. :wink:

On another note, here’s a thought: I guess most of you know that Airbus is building the wing box of the A380 in the same carbon fibre material as most carbon seat posts (yes, I know different lay-up); same applies for the entire hull of the Boeing Dreamliner. Given that a 85kg man can fatigue fracture a 27mm diameter, with 3.something mm wall thickness, I am looking forward to my first flight in one of those :confused:

john…were you at the habs game last night?

No sir.

AJ, to be fair your saddle is so far setback you’ve got a massive bending moment at the clamp point. Bumps + heavy guy with that sort of loading can’t be a good thing and not something that was designed for in the tube. I’d be really scared if it failed on the tension side though!

I’ve worked enough in aerospace (almost entirely in engine controls but you obviously hear stories and the old guy that did the cert work did lots of airframe stuff too). They took a long time to get the fatigue failure of alloy airframes and required testing down pat so I wouldn’t be surprised if there was a teething period for composite structures - I still feel infinitely safer getting onto a composite airframe than I do driving around in traffic (on a bike or in a car).

John, the fact you’ve got the longitudinal crack suggests to me its a crushing from torquing so if everthing was done to spec the part was probably defective and you had best get it returned for $$$.

Speaking of seat/saddle problems - I obviously didn’t torque my rails tight enough after adjusting and the saddle slipped back several cm from where it should be over the bumps, which probably explains why just about everything hurt yesterday and my back and IT bands were a total wreck.

related question: When I look at the bottom of my seatpost, which I always thought was carbon, I realize that it’s actually METAL wrapped with carbon. What’s the deal? And does this mean I don’t have to worry about it snapping under me?

Hey Ben,

I had the same surprise when i flipped my supposedly carbon seatpost too. So its a marketing trap/scheme for noobs (like me) and i can prove it: I went into another bike shop with the same bike as mine and asked the sales man and he was “selling” me a bike with a carbon post. Nonethless it maybe has one good application, which is that the seat post is probably less likely to get jammed into the seat tube with that carbon layer.

so no worries if you see a crack, i would say

Unfortunately you fellas are new sacrifices at the altar of successful marketing. Carbon wrapped aluminum components are appreciably heavier and still weaker than high quality aluminum posts - though they usually cost more. The mystical “vibration-absorbing” qualities of carbon don’t factor in when it’s your seatpost, either. Sorry to be the bearer of bad news.

A lot of companies sell very light, very strong forged aluminum posts - that’s what I’d look at for future upgrades.

[quote=“LgReno”]

so no worries if you see a crack, i would say[/quote]

just to be clear, it doesn’t matter what material your seat post, or any other component for that matter, is made out of.

if you see a crack, stop riding and replace that part.

[quote]just to be clear, it doesn’t matter what material your seat post, or any other component for that matter, is made out of.

if you see a crack, stop riding and replace that part.[/quote]

AL alloys typically give you warning in the form of fatigue but then brittle fracture as well - if you see striations on any bike part Scott is right, time to chuck it out.

[quote]Unfortunately you fellas are new sacrifices at the altar of successful marketing. Carbon wrapped aluminum components are appreciably heavier and still weaker than high quality aluminum posts - though they usually cost more. The mystical “vibration-absorbing” qualities of carbon don’t factor in when it’s your seatpost, either. Sorry to be the bearer of bad news.

A lot of companies sell very light, very strong forged aluminum posts - that’s what I’d look at for future upgrades.[/quote]

While many of the carbon wrapped Alu parts are a cheapo marketting scheme, there is good engineering sense behind the design principle, in particular for parts that need to be clamped on. I suspect there is actually a design optimum of having an alloy core with a carbon wrap when you design for both load bearing (compression/bending) and crushing. You just don’t see that in a cheap carbon wrap post.

You can design a competitive wrapped part, however and its been done.

I’m pretty meh on those ultra light weight alloy parts too - they tend to be really brittle.

Also alloy has its own marketting foibles - scandium is a bit of a joke. Interstitial scandium does make for very strong Alu alloys, but the relative cost is such that its a loosing proposition against Ti alloys.

Titanium frame costs are also massively overpriced due to marginal difficulties in welding which means you actually have to know what you are doing - as opposed to steel which any idiot (including myself) can weld with basically no experience.

Also, the sheer quantity of alloy parts that do not undergo proper/optimal heat treating is pretty scary.

Jason: What about magnesium as a frame/component material. It’s very light and has been used in automoive sports, though this has led to some spectacular race car fires (obviously for bicycles that wouldn’t be a problem).

Why no love, apart from a few rare case, for ‘mag’?

I’m no metallurgist, but can magnesium even be shaped into tubes i.e. is it a ductile metal?

You never work with pure Mg, its usually alloyed with Alu. There are some out of this world Mg-Li alloys but they are impossible to get due to lack of supply chain right now.

Mg is comparatively high cost (supply and supply chain issues), it’s quite difficult to weld or braze and it’s still lower in terms of strength to weight than CF.

You can form Mg easily just like other alloys (machining, “heating and beating”), and you can also do powder cintering like some other alloys.

You don’t get any real benefit for the cost to justify Mg over CF unless you really need a custom geometry (<1% of all riders). At the lower end you can’t justify the cost of Mg over the 25% or so strength to weight increase over Al.

Only Ti is comparable to the best strength you can get with CF and its ultimately quite a bit denser.

What I’m surprised at is that you see very few high end Alu road bikes - 7075 Alu is relatively cheap, and impressively strong. It makes little sense to me that the soloist is one of very few competitive alloy bikes out there since there is IMO a huge market for that level of mid range performance.

Ditto with titanium (although its not as easy to hydroform as Alu), its only the MTB crowd that hasn’t fully been taken over by the CF mafia and you see more and more CF MTBs every year.