A good reason to not buy an FSA Carbon Pro seatpost

I think this was the cheap carbon wrap version - ridden on my commuter @ 70m per week

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installation error?

Burrs on the inside of your frame or it looks like you forced the wrong size in. Either way it looks more like an installation error rather than flaky wrap.

Out of curiosity is the seatclamp on the front or back of the seattube?

Right size - not bothered about the wrap coming off - bigger issue is the huge t shaped crack that covers half the circumfrance of the post!!!!

Out of curiosity is the seatclamp on the front or back of the seattube?

Bolt at back

right size is a relative term......some seatpost come fraction of mm bigger or smaller than others and so do seattubes.......for instance you can a have 27.2mm frame where one of the two same size seatposts will slip the other one wouldn't....looks like yours was fraction bigger despite frame and post being same size......plus bolt at the back and carbon is something lot of people wouldn't recommend

right size is a relative term......some seatpost come fraction of mm bigger or smaller than others and so do seattubes.......for instance you can a have 27.2mm frame where one of the two same size seatposts will slip the other one wouldn't....looks like yours was fraction bigger despite frame and post being same size......plus bolt at the back and carbon is something lot of people wouldn't recommend

Stock post had the size on it - also measured tube - however if stock post was wrong and my tape measure skills poor then fair play. What's the issue with bolt for full carbon btw - pressure applied in non-optimal direction (in this case just a wrap post however so standard alloy post beneath)

seatposts are not all exactly the size stated, serotta warned me that a thomson 27.2 seatpost is often fractionally smaller, though this is not such an issue with aluminium posts

seatposts are not all exactly the size stated, serotta warned me that a thomson 27.2 seatpost is often fractionally smaller, though this is not such an issue with aluminium posts

Good tip - however whats the way of telling (apart from trial and error). With your point in mind I wonder if the alloy core was correct size but then the wrap took it up my a few mm - or the other way round) - what is more likely to cause a crack from general use - post too small or too large?

my guess is the post was slightly too narrow and then the bolt over tightened, so the seat tube/clamp angled in a little and gouged away at the seat post.

^ what he said - the fact that the crack is inline with the area of greatest pressure suggests that.

As for the clamp position, there's a school of thought that says where you have a external seat clamp, the bolt section should be on the opposite side to the slit. Altho I've heard others say it doesn't matter as long as the right torc is used.

FWIW if you want an inline carbon post, I have this outland one.

Well priced, good seat clamp mechanism, and has lasted me well. It's not superlight or anything, but it's held up well on several frames. Also as it's an mtb post I'd guess it's designed as being slightly tougher(?).

my guess is the post was slightly too narrow and then the bolt over tightened, so the seat tube/clamp angled in a little and gouged away at the seat post.

Good bit of Holmes deduction!! What's the best tip about fractional sizing (forum advice or is there anything more formal?) maybe my Allen key could do with a Gauge...(used to have a hex key with gauge for my Audi roof bars which stopped over tightening )

FWIW if you want an inline carbon post, I have this outland one.

Well priced, good seat clamp mechanism, and has lasted me well. It's not superlight or anything, but it's held up well on several frames. Also as it's an mtb post I'd guess it's designed as being slightly tougher(?).

Thanks for suggestion - am building up a hardtail Mtb (just sold the ss to fund) ans sourced a Thomson elite for cheap)

use a torque wrench to tighten to the required amount

http://www.wiggle.co.uk/ritchey-torque-key

Stock post had the size on it - also measured tube - however if stock post was wrong and my tape measure skills poor then fair play. What's the issue with bolt for full carbon btw - pressure applied in non-optimal direction (in this case just a wrap post however so standard alloy post beneath)

Don't use measuring tapes, get a vernier calliper, even the cheap plastic ones are better than tape. It's a good habit to check parts with slip fit (seatpost) or interference fit (headset) before fitting - manufacturing tolerances can work against you.