Buying used carbon frame

ubergn0men

Been searching like a crazy person for a good first bike, and finally found a used one which seemed pretty good. It's a XC race bike build with 26" wheels and it has been used.

Problem is, the carbon frame has some paint marks from what appears to be crashes. Seller says it's not a problem though, as it has been used for two seasons after they occoured.

Is there some way to know if it's just cosmetic? Should I be able to see cracks going from the marks if it were to be a problem?

The bike will probably be ridden pretty hard on trails. Would be a sweet bike if I could be sure it would hold up.

supersonic

If they are paint marks, then they will come off - see what it looks like underneath.

stubs

A mate knows a bit about carbon fibre and used to make canoes reckons if the gel coat is cracked or starting to show broken/seperated fibres then avoid it. If its just an impact mark where a stone has struck or the bike has hit the deck its fine, apparently you could whack a carbon frame with a ball pein hammer and not damage it any more than cosmetically. Carbon fibre can sometimes be repaired as well if you can go over a waterfall and smash a canoe into a rock and repair it a frame should be fixable though wouldnt know where to send it.

When a carbon frame snaps (which they do) its news when an Ally frame snaps (which they do quite regulary) no one takes any notice

supersonic

And when steel snaps, nobody says anything at all ;-)

stubs

supersonic wrote:

And when steel snaps, nobody says anything at all ;-)

Steel can not snap it is indestructible and if you say any different a bunch of sandal wearing hippies will come and stare at you sadly and shake there heads muttering "Steel is real man"

Did manage to bust a brazed frame once but it just needed a torch, filler rod and some flux to repair. Probably a badly fluxed joint or didnt get it hot enough for the brass to flow. My brothers 1st MTB was a proper lugged Reynolds 535 frame now that was indestructible its still running 30 years and about 5 owners on as a commuter.

Clank

stubs wrote:

A mate knows a bit about carbon fibre and used to make canoes reckons if the gel coat is cracked or starting to show broken/seperated fibres then avoid it. If its just an impact mark where a stone has struck or the bike has hit the deck its fine,

This^

stubs wrote:

apparently you could whack a carbon frame with a ball pein hammer and not damage it any more than cosmetically.

But not this.^^ The internal surface, or the internal structure, of the tube can suffer from micro cracks and inter-layer delamination's, which will eventually lead to same issues as if the cracks were on the outside.

stubs wrote:

Carbon fibre can sometimes be repaired as well if you can go over a waterfall and smash a canoe into a rock and repair it a frame should be fixable though wouldnt know where to send it.

This^^

njee20

I'd say trust your judgement. If it's got a few shallow scuffs and looks pretty tidy, buy it. If it's got deep gouges, the paint's hanging off and it looks trashed, then walk away!

That said... 26" XC race bikes are very out of favour presently, so there's likely to be a good number of bargains about!