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Unraveling/Disintegration of Seat Tube of Giant Trinity
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2018 Giant Trinity Advanced. Mechanical.

Custom paint job - removed factory paint, now nude carbon with protective UV lacquer.

The bike is new and has been used on indoor (Wahoo Kickr) for most of the time.

However, 2 long rides - one last weekend (17 Feb 2019), has resulted in this peculiar disintegration of the bottom tip of the seat tube. It is the area closest to the wheel. There was no obvious scratching, bumping or other mechanical/physical lesion which occurred on the ride, which could have caused this damage once off.

I am fairly sure, (based on the sudden worsening of this damage after the second long ride) that it is the dust/grit kicked up from the tire that causes this damage. There was a slight separation of the UV lacquer from frame after the first long ride, however, I thought that was the spray artist's fault. Now I know it has something to do with the riding dynamics.

I fear this might be a problem only I have, however, I would appreciate any advice.
Last edited by: Spyker: Feb 18, 19 22:50
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [Spyker] [ In reply to ]
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Some pictures would be heelpful
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [davidalone] [ In reply to ]
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I did upload 2 but they're not showing?!?! Will try again.
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [Spyker] [ In reply to ]
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Any pictures with the wheel in place ? Would be interesting to see the spacing etc. Both close up and a 'general' view.

What wheel and tyre ? Spoke count ? (Or is it a disc) ?

How big / heavy are you ?

Also how much 'depth' of material do you estimate is is 'missing'
Last edited by: BobAjobb: Feb 18, 19 23:48
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [BobAjobb] [ In reply to ]
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I will place in the wheel later after work and post better pictures. I didn't have time before work today. Girlfriend took pics at home, and she was obviously tired and without her glasses.


The Setup:

- Profile Design 58/24 carbon wheels (both are therefore 58mm deep);
- Continental Gatorskin tires;
- I guess normal spoke count. Nothing peculiar.
- I am 180cm and 72kgs / 158.7 pounds

Depth of material missing is about 2-3mm. A type of damage that seems gradually and finely inflicted. The exposed carbon seems brittle and powdery. Particles falling off as I touched the damaged area.
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [Spyker] [ In reply to ]
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That does not look good. From the pictures and description it seems like damage which is common on Specialised Transitions on the frame right behind the fork (The triangle point thing in this picture http://www.tritalk.co.uk/...wtopic.php?p=1258104). On Transitions what happens is the tip of the triangle gets broken/smashed by the fork or when the bike is transported. This then exposes the carbon and the whole area starts to disintegrate especially it gets a lot of road spray.

I can imagine the seat tube got damage/over sanded during the re-spray the same effect would happen. The damage would have been subtle at first but you are correct that grit coming off the rear wheel would have quickly made it much worse. It doesn't look like the damage has reached a critical structural area of the frame yet so it is probably repairable. Critically you want to seal off that area before the damage gets worse. If the damage works its way into seams in the carbon layup connecting the seat tube and seat stays any repair work will become significantly more challenging.
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [scott8888] [ In reply to ]
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Your comment on the damage occurring during respray sounds true. The initial 'damage' was more like a separation of the lacquer from the frame - kind of like a surfboard's waterpaper starting to peel off. I noted it, but thought it was a stationary / non-progressive issue.

Either way I will definitely have it reinforced and sealed before my next ride. Obviously with a more durable resin/lacquer/glue.

Its just bizarre that such slight offset of grit can suddenly cause such damage. During the ride in which the damage occurred did 93km at speeds of 45-55kmph down and 30kmph back up.
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [Spyker] [ In reply to ]
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During lunchtime I could investigate a bit more detailed and I found the problem.

After receiving the bike, I had the saddle post cut twice to fit my length. On the second cut of its length, it turned out to be the perfect length so as to rest on the bottom of the seat tube and be my desired height.

I then fastened the saddle post clamp lightly to ensure no wriggling or shaking would occur during riding. I knew it would not slide down anymore, since it was resting on the floor of the seat tube.

Well, the floor of the seat-tube is not a flat reinforced base as I thought it would be. There is, in fact, no base - the frame is hollow all the way through down the seat tube to the BB. (Sorry for being so uninformed).

So the bottom of the saddle post had started shearing through the one corner of the seat tube where the latter had presented a contact point with the former. Point of contact being right at rear of seat tube, before it starts to bend with the circumference of the wheel.

Lesson: integrated saddle posts are not a DIY system. Use your saddle post clamp correctly! I will have it cut again, clamp it securely, and seal up damage.
Last edited by: Spyker: Feb 19, 19 4:10
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Re: Unraveling/Disintegration of Seat Tube of Giant Trinity [Spyker] [ In reply to ]
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Glad you've sussed it.

As per others I'd agree that 'point' won't be particularly structurally loaded (once seat post sorted, and DO use carbon grip paste on the post to stop it slowly slipping down and causing the same prob again - my tt bike seatpost always slips without it).

And I thought exactly the same re get it smoothed off and then some good extra laceur. I'd even be tempted to then try get a bit of 'helicopter tape' or similar onto that area just to give some extra protection from grit, salt and any occational stone-stuck-on-tyre.

I'd just double check after all that, that there is clearance with the tyre (and more than 2 thou !) Esp when you're weight is on the saddle in case there's a small anount of flex.

Anyway, good luck !
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