J
Jay Beattie
Guest
<[email protected]> wrote in message
news:[email protected]...
> Chalo Colina writes:
>
> >>> I bent a very stout steel tandem downtube this way. Car
turned in
> >>> front of us, front tire hit car fender basically
straight-on,
> >>> downtube buckled, no appreciable wheel damage.
>
> >>> Buckle looked very similar to the pictures posted by Chalo
in
> >>> later posts.
>
> >> However, the "buckle" on Chalo's Cannondale doesn't look
like that.
>
> > Jobst, if I recall correctly, you ride a steel bike of
conventional
> > construction and tubing diameters. Don't you find it
unsurprising
> > that a thin-walled, huge diameter, conical tube would display
a
> > different-looking failure mode? I find it a little
disappointing
> > that the only alternate hypothesis you can offer is I must
have
> > slammed it in a car door or the like.
>
> I don't see where you get that idea. I don't think I mentioned
> anything about a collision with a solid object like a car.
>
> > I don't know why it seemed that the front wheel stopped and
tossed
> > me over the bars, but I do know that it happened an instant
after
> > the pictured frame failure occurred.
>
> I think you'll notice that this was not a "frame failure" but a
small
> damage to the downtube, one with which the bicycle was fully
> functional and could be ridden with no change in perceptible
riding
> characteristics. The downtube was in perfect lateral
alignment,
> therefore having no effect on steering. Change in rake was so
> minimal to be insignificant. That the strength of the tube was
> compromised by the knick is obvious.
>
> > So far I have three reasonable possibilities:
>
> > first, that the tire made contact with the downtube somehow
without
> > leaving a mark on the paint;
>
> That is possible but that case cannot be reconstructed
according to
> others who have seen the fork compressed and still leaving safe
tire
> clearance to the downtube. If this was the cause and the tire
made
> contact, there may still not have been a skid mark because the
tire
> was not rotating significantly... near lock-up anyway.
>
> > second, that the frame's failure caused a sudden shift in the
front
> > contact patch which made the difference between hard
deceleration
> > and an endo;
>
> That description escapes me. I can visualize that a sudden
brake
> application could stop the tire as the fork compresses but not
at
> 30mph. If you mean that this was a typical endo cause by the
rider
> sliding off the saddle, yes that is a possibility, but that is
a rider
> induced event, not one of mechanical failure. The assumption
was that
> you are experienced enough to not cause such a crash... having
> probably read about it here often enough.
>
> http://draco.acs.uci.edu/rbfaq/FAQ/9.36.html
>
> > third, that some malfunction occurred in the brakes that was
not
> > obvious afterwards when I was walking the bike home.
>
> I assume you tried the brake or had someone else try that, but
I don't
> see any pointers to a brake lockup. Even that would not have
caused
> the dent in the downtube shown in the photos that is not a
compression
> wrinkle.
>
> > I am grateful for relevant observations, but I have already
related
> > the circumstances of the failure. It was not a result of any
> > object's impact on the downtube unless that object was the
front
> > tire.
>
> As I pointed out, the words that you were tangled in the
bicycle after
> the crash gives rise to the possibility that the dent was cause
after
> the dismount and possibly by a shoe stuck between tire and
downtube.
> This dent appears as an embossed one made by a radial force on
the
> tube rather than a sliding contact such as a tire. Tire
contact would
> also have been about half way up between the dent and headtube.
Would deformation of the top tube be expected if this were a
frame failure? -- Jay Beattie.
news:[email protected]...
> Chalo Colina writes:
>
> >>> I bent a very stout steel tandem downtube this way. Car
turned in
> >>> front of us, front tire hit car fender basically
straight-on,
> >>> downtube buckled, no appreciable wheel damage.
>
> >>> Buckle looked very similar to the pictures posted by Chalo
in
> >>> later posts.
>
> >> However, the "buckle" on Chalo's Cannondale doesn't look
like that.
>
> > Jobst, if I recall correctly, you ride a steel bike of
conventional
> > construction and tubing diameters. Don't you find it
unsurprising
> > that a thin-walled, huge diameter, conical tube would display
a
> > different-looking failure mode? I find it a little
disappointing
> > that the only alternate hypothesis you can offer is I must
have
> > slammed it in a car door or the like.
>
> I don't see where you get that idea. I don't think I mentioned
> anything about a collision with a solid object like a car.
>
> > I don't know why it seemed that the front wheel stopped and
tossed
> > me over the bars, but I do know that it happened an instant
after
> > the pictured frame failure occurred.
>
> I think you'll notice that this was not a "frame failure" but a
small
> damage to the downtube, one with which the bicycle was fully
> functional and could be ridden with no change in perceptible
riding
> characteristics. The downtube was in perfect lateral
alignment,
> therefore having no effect on steering. Change in rake was so
> minimal to be insignificant. That the strength of the tube was
> compromised by the knick is obvious.
>
> > So far I have three reasonable possibilities:
>
> > first, that the tire made contact with the downtube somehow
without
> > leaving a mark on the paint;
>
> That is possible but that case cannot be reconstructed
according to
> others who have seen the fork compressed and still leaving safe
tire
> clearance to the downtube. If this was the cause and the tire
made
> contact, there may still not have been a skid mark because the
tire
> was not rotating significantly... near lock-up anyway.
>
> > second, that the frame's failure caused a sudden shift in the
front
> > contact patch which made the difference between hard
deceleration
> > and an endo;
>
> That description escapes me. I can visualize that a sudden
brake
> application could stop the tire as the fork compresses but not
at
> 30mph. If you mean that this was a typical endo cause by the
rider
> sliding off the saddle, yes that is a possibility, but that is
a rider
> induced event, not one of mechanical failure. The assumption
was that
> you are experienced enough to not cause such a crash... having
> probably read about it here often enough.
>
> http://draco.acs.uci.edu/rbfaq/FAQ/9.36.html
>
> > third, that some malfunction occurred in the brakes that was
not
> > obvious afterwards when I was walking the bike home.
>
> I assume you tried the brake or had someone else try that, but
I don't
> see any pointers to a brake lockup. Even that would not have
caused
> the dent in the downtube shown in the photos that is not a
compression
> wrinkle.
>
> > I am grateful for relevant observations, but I have already
related
> > the circumstances of the failure. It was not a result of any
> > object's impact on the downtube unless that object was the
front
> > tire.
>
> As I pointed out, the words that you were tangled in the
bicycle after
> the crash gives rise to the possibility that the dent was cause
after
> the dismount and possibly by a shoe stuck between tire and
downtube.
> This dent appears as an embossed one made by a radial force on
the
> tube rather than a sliding contact such as a tire. Tire
contact would
> also have been about half way up between the dent and headtube.
Would deformation of the top tube be expected if this were a
frame failure? -- Jay Beattie.
