Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am looking at a carbon framed road bikethat has me concerned.On the topside of the bottom bracket,drive side there is a very small hairline crack in the paint.The seller states that it has been there for two years with no change.He was told by the dealer that it is just in the paint and a fairly common occurence.Anyone else experienced this?It is a three year old cervelo.The crack is 3/4 inch long and you can't feel it with a fingernail.

share|improve this question
How about this: Buy the frame, take it to someone who does bamboo frames, and have them wrap the area as if it were a bamboo frame. – Daniel R Hicks Mar 11 '12 at 13:08
Here's a link on with a 10 step process for examining a used carbon bike. It's somewhat detailed and may be of use to you. – user313 Mar 12 '12 at 22:01
A used bike is a risk. A used carbon bike is a bigger risk. Factor that into what you are willing to pay. I got one at such a good price if the frame was cracked it was still wroth the it for the components. – Paparazzi Aug 11 '14 at 17:39
up vote 3 down vote accepted

Why don't you take the bike to a Cervelo dealer and have them check it out?If the seller of the bike is being honest with you it shouldn't be a problem> Last year I had a horriffic crash with my Trek Madone going over 20mph and the only damage my frame sustained was a small chip in the frame. otherwise the frame is perfectly sound.

share|improve this answer
Seller has agreed to a conditional sale based on the frame being evaluated by a competent carbon frame shop.I don't really trust the dealer evaluation based on the number of frames they see.There is a independent shop that does repairs within driving distance. – mikes Mar 12 '12 at 19:59

Markus Storck, lead engineer and owner of German carbon frame powerhouse Storck Bicycles, told me at a conference about 3 months ago that the best ways to tell if a frame is cracked are movement and time.

Movement, because a crack will flex if it's through the paint into the carbon, and you put pressure on the center of the crack, and time, because a crack will grow with time if it's more than paint.

If you are even halfway concerned with a crack, don't buy the frame.

It's just not worth the risk, unless you can afford to be wrong about the frame's ride-ability.

I hope that helps.

share|improve this answer
+1: Whenever there is any doubt, there is no doubt. – OMG Ponies Mar 11 '12 at 20:38
Too right. If you have to ask, it isn't worth the risk. – zenbike Mar 12 '12 at 14:54
It is worth the risk if the other components are worth the price. I bought going in that if I had to buy a new frame it came out a wash and all the components were components I would have selected. And 6 months later no frame problems. Because of the scare factor on carbon you can get some great deals. – Paparazzi Aug 11 '14 at 18:32

If you can't feel it with a fingernail, the crack probably isn't in the carbon. Another trick is to whack the tube with a quarter over and around the crack. Do the same at a similar location that doesn't have a crack. If there are any differences in sound, the frame has probably sustained damage.

For what it's worth, I bought a bike with very similar circumstances in December. I used a piece of tape to mark the beginning and end of the crack, so I can watch for any expansion. No movement so far.

share|improve this answer

The BB and head tube are some of the thickest carbon parts. Listen to sound differences around it, but I think these areas would be some of the last places to crack. Most cracks would occur either at a junction, thin spot, like middle of the down tube.

Also, if the crack you see has no marring, chipping or other damage on either side, its probably superficial. Cracks caused by outside forces (impact) would leave other evidence on the paint, like scuffs, chips, etc.

share|improve this answer

Have a look at AFAIK there is no other way to find structural issues in carbon frames.

Everything else is just guesswork. Even a competent dealer cannot look into the fibers.

So if the frame is checked on the surface only, i wouldn't buy it.

share|improve this answer

protected by Gary.Ray Aug 11 '14 at 18:54

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.