Is this a crack in the paint or carbon?

Discuss light weight issues concerning road bikes & parts.
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by bikerdan

Friend of mine has a crack on his frame in front of the seatpost on the top tube. When he pushes down on the saddle it looks like crack gets wider

Anyway to tell if it's only the paint or if the carbon is also cracked?Image

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by Weenie

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by Pieke

If pushing makes it more obvious, it's probably in the carbon. Hard to tell with 100% certainty without a scan or taking the paint off.

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by billspreston

That looks like a true carbon crack to me. Looks like there was an impact from the side that rubbed some housing off onto the tube right where the crack starts? Try tapping the area with a coin to listen for changes in sound on the crack. If there is no crack on the opposite side, tap the coin there and see if it sounds the same as the cracked side.

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by miltmaster3

Carbon crack

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πατα τραβα ρε

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by DJT21

Isn't white paint less flexible than other colours, and hence is more likely to develop cracks?

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by dcorn

I would argue that the paint would not have cracked in that orientation without some serious flex in the carbon at that point. Is that the bottom of a seatmast? Not a place I'd want a failure to occur.

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by bikerdan

Yeah it's at the bottom of the seatmast

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by mattr

bottom of the seatmast, looking backwards. Exactly where you'd expect it to fail after something like a big impact to the saddle (pothole etc) or an over long mast. (or seatpin in a more standard frame)

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by simoncx

Looks like a crack, my frame cracked in the same spot 2 weeks ago. Does the bike feel softer when riding seated, almost like riding on low psi?

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by beanbiken

Expect Carbon crack other wise it has over-flexed enough for the paint to crack and that does not bode well for the underlying structure. Personally would not ride until actual damage/integrity was confirmed

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by Lewn777

Yeah I had a crack in my old Fuji there. Seem a common place to develop a crack if you run too short a seatpost or the area isn't strongly enough reinforced by the manufacturer or you just hit a pot hole or something hard enough. Frame is toasted very probably. A tip: if you can warranty the frame tell them you were using the OEM seat post which was uncut.

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by reedplayer

probably carbon crack, but maybe not, because white colour is very vulnerable for paint-cracks.
berfore "toasting" the frame, i would remove the colour and take a look on the uncovered carbon surface.

for example: i asked "BMC" if those cracks on my frame are structural or simple paint cracks, and if i can use the frame furthermore. they confirmed its only stress cracks of the paint and frame can be used with confidence.


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by wheelsONfire

Almost impossible to say. The seatpost area do flex. If you'd look at a person biking on a trainer, you could probably see that a frame flex quite a bit.
But one thing in all this which is very strange.
Looking at my old R1, the side fairings flexed very much by design. That paint never cracked.
I think it's the same for race cars?
But on bikes,.... i don't know why, but paint seem to crack much more easy.
Anyway, i have same on my gravel bike. Same region!
It's only one way to know for sure, that requires sanding off the paint.
Or a CT scan

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by oldnslow2

Try tapping it with a quarter and listen for changes in the sound.

If it is cracked, send it to Calfee. They fixed my Emonda SLR.

by Weenie

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by Catagory6

oldnslow2 wrote:
Wed Mar 06, 2019 2:33 am
Try tapping it with a quarter and listen for changes in the sound.

If it is cracked, send it to Calfee. They fixed my Emonda SLR.
does calfee do all the scanning with the dyes and sonograms and stuff?

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