Bicycle Mechanics - Checking a carbon fork for damage
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08-10-10, 11:12 AM
Hey everyone. I recently killed the rear seatstay on my CAAD9 in a crash and purchased a new one. However, the new bike is white and I really don't like the look of the white fork - I'd prefer the bare carbon fork that was on my matte black bike as it will contrast well with the black accents on the bike.
The problem is that crash was pretty bad - 43mph according to my computer and about 60-70 yards of tumbling and sliding. The rear rim is tweaked about 3/4" out at one point but the front rim is still 100% true so I'm assuming it never took a major hit - even though it was the point of impact that threw me over the bars when I hit a sunken in section of concrete.
So do you think the fork would be cool to throw into the new bike? How would you check or who would you have check it in southern California to make sure it's not damaged? It's a steel steerer Cannondale Ultra fork btw.
08-10-10, 11:16 AM
CAT scan/ Xray?
08-10-10, 11:57 AM
If there's no obvious cracking damage showing there's still the issue of internal delamination that is hard to find. Two methods of checking it yourself come to mind. First off hold the fork by the steerer and using a screwdriver handle tap the legs all over and listen to the sound. Taps on each leg in the same place should sound the same. Any sort of drastic change in the sound is likely caused by some delamination. Assuming the fork passes the sound check then I'd move on to a flexing check. For this you need to grip the steerer in some manner that will hold it very firmly. Something like a block of wood with a 1 1/8 hole that is sawn through and then the blocks and fork are clamped to a door frame or in a vise attached to a heavy immovable bench. Once secured I'd flex the legs inwards, outwards, to the front and to the rear. What you're looking for is for both legs to flex equally. If one flexes more than the other then again there's very likely internal delamination. And if it snaps like a dry turkey wishbone then again you have your answer. Don't be gentle with it. You should be using enough pressure to flex the legs by about 1/2 inch to properly simulate the sort of load it'll see on the road. This will be quite a bit of tension and it may be hard for you to do this and still look for even flexing in both legs. So it may help to have a spotter watching and measuring things.
As BCRider explained there's no reliable way to test. If it were anywhere else on the bike, I'd follow his methodology and make a judgment call, but it's a fork and I hold those to the highest standards.
Whenever I plan to ride anything which I'm not sure I can trust, I use my "likelihood & consequences index" to help me decide. In the case of a suspect carbon fork the potential consequences of a failure (a sudden unannounced introduction to the pavement) are so severe that I'd need assurance of near zero likelihood of failure before I'd ride it. That level of trust would require destructive testing to verify, so for me it would be a pass.
08-10-10, 02:57 PM
I wouldn't take a chance. Besides you can save a lot of weight buying a new fork with CF steerer.
08-10-10, 04:30 PM
That is the ultimate plan. I have 3T bars, stem, and seatpost coming so I'm thinking their fork would nicely round out the set. An all black fork may look a little goofy (tried the bare carbon Cannondale on today and I'm not sure I like it) but the somewhat boldish white logo and lines on the 3T fork will balance against the white frame nicely. I'm just in the middle of a Red buildup so I'm a little short on cash. I'm also awaiting an email for the max rider weight recommended as I'm still hovering in the 210-215 range (at 6'2") as of late and I want to make sure it's not like the Easton full carbon that has a lower limit.
I was thinking that since I didn't like being formally introduced to Crenshaw Blvd. at 43mph the first time, I really was not about to do it again over a $100 fork unless I could be sure it would be safe. It seems all the necessary methods aren't worth the trouble or cost. Besides, the right side seems to flex more the left and that was the side I ended up coming down on after sliding and rolling around a while.
Thanks for the advice everyone. It seems white fork it is until I can afford a new one.
08-10-10, 05:08 PM
Actually with the sober second thought I'm with the others. If it was something that epic I don't think I'd trust my face to the old fork either. This is why I just don't want to bother with carbon stuff in the first place. Or at least up to NOW I've managed to avoid it.
EDIT- And I just saw what you wrote about the right side seeming to be a bit more flexible than the left. That's the deathsong for that fork. Amputate the legs now with a saw (outside with a dust mask on please) and discard it before someone thinks it's OK to use.
If it was something that epic I don't think I'd trust my face to the old fork either. This is why I just don't want to bother with carbon stuff in the first place. Or at least up to NOW I've managed to avoid it.
(Off topic) I should have known you were a fellow metal man. fb
08-10-10, 06:16 PM
Steel is real Baby! :D
08-10-10, 06:50 PM
Well if I could find a nice aluminum fork or even better, a stiff titanium one (will go well with my Lynskey I'm ordering in October), I'd look into that. I'm about as far from a weight weenie as I really can be because I know that 100g on the bike means dick when I'm carrying around an extra 40lbs on my frame.
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