> we debated this a while back. care is indeed needed, and quality varies
> substantially with manufacturer [VERY bad experience with chinese-made
> kestrel forks]. but to remind you, this ratio is not just weight for
> weight. reynolds forks had graphs showing their forks /three/ times
> stronger than steel for less than half the weight. this is entirely in
> accordance with my attempts at destruction. i have bent several steel
> forks over the years and relatively low stresses. the two carbon forks
> i've "tested" have been much stronger. and frankly, if i was on the bike
> at impact levels sufficient to break them, i'd be in the e.r. regardless.
The problem is that you don't know how much impact the fork actually took,
but common sense says that, at 15mph, it was a fair amount. Yes, carbon
fiber is dramatically stronger (for its weight) than steel, but there are
limits, and you just don't know where those limits are until it fails. Not
with present fork technology anyway; that will change in the future as
manufacturers work on the holy grail of the carbon component industry...
designs that indicate that limits have been exceeded prior to actual
failure. But we're not there yet.
Here's the really scary thing. Back in the day, we sold a *lot* of
replacement forks, when forks were made of steel. People ran into cars or
crashed into things, whatever, and bent the forks, so they had to get new
ones. Now? Virtually zero replacement forks. In my estimation, as many, or
more people, are riding road bikes now as back then. And they're still
crashing into things. Crashes which, since they would have bent a steel
fork, are reasonably expected to be beyond the design criteria for a carbon
fork. But instead of replacing them, people think whew, fork looks OK, got
away with that one, don't need to spend all that $$$. And then a subsequent
minor event finishes off the damaged (but not visibly so) fork and you have
the makings of a JRA story (I was just riding along and my fork broke in
two).
If your fork took a heavy hit, assume the worst. There are very few things
your life depends upon more than your fork staying intact.
--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA
"jim beam" <
[email protected]> wrote in message
news:
[email protected]...
> Qui si parla Campagnolo wrote:
>> jim beam wrote:
>>> bg wrote:
>>>> I got hit from the side the other day. Car was going maybe 15mph.
>>>> Bumper hit my knee and front wheel. Knocked me off the bike. Bent the
>>>> wheel. No obvious damage to the fork or carbon rear stay and I left it
>>>> with the LBS to check out. But absent any visible wrinkles how much can
>>>> one trust carbon stuff esp the fork bars and stem after a shot like
>>>> that? It's got a carbon steerer. I had a StupidLight seat post break
>>>> last year unexpectedly
>>> collar probably over-tightened and cracked the tube.
>>>
>>>> (I weigh 140lbs) so I'm kinda leery of trusting
>>>> the fork.
>>>> thanks,
>>>> bill g
>>> do the squeeze test. [google for details] if it passes, keep on riding
>>> it. carbon is stronger than steel. scratches in the clearcoat mean
>>> nothing. i have carbon forks that have been in impacts severe enough to
>>> give haematomas in the palms on both hands and to smash rims - and both
>>> forks are fine. i'm #205.
>>
>> You gamble with this gents teeth pretty readily. Carbon is stronger
>> than steel for a given weight. Carbon use is lots lighter than steel,
>> so not necessariluy 'stronger'. Steel bends, carbon breaks.
>> We have had customers that have broken carbon handlebars, seatposts,
>> rims, frames and forks.Many JRA..so MY suggestion is you be careful.
>>
> we debated this a while back. care is indeed needed, and quality varies
> substantially with manufacturer [VERY bad experience with chinese-made
> kestrel forks]. but to remind you, this ratio is not just weight for
> weight. reynolds forks had graphs showing their forks /three/ times
> stronger than steel for less than half the weight. this is entirely in
> accordance with my attempts at destruction. i have bent several steel
> forks over the years and relatively low stresses. the two carbon forks
> i've "tested" have been much stronger. and frankly, if i was on the bike
> at impact levels sufficient to break them, i'd be in the e.r. regardless.