Frame Flex

RU' may have said:

The question is this: is this 'normal' for a (relatively) light-weight steel frame?

No.

Quoted message said:

Or is this an unusual (and dangerous) amount of flex, specific to this bike?

It sounds like there's a failure in process in one of the joints. It may be more economical to
replace the frame than fix it if that is the case.

Quoted message said:

I would hope to be able to upgrade to a stiffer frame, probably another steel frame, without
spending a fortune, but I want to be sure that I will be able to eliminate this problem by doing
so. Any thoughts?

Any decent frame should not have that much flex. What you describe is typical of a frame that is in
the last stages of failure. I wouldn't ride it. Have a local bike shop take a look; they can
probably spot the failure point in short order. I'd look at the top tube's joints first. If cost of
repair is an issue, consider shopping for a used frame that's in good shape.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy.

try getting something with oversize top & down tubes. "oversize" means larger diameter than the seat
tube. this is particularly important if you use a large size frame.

RU said:

The frame of my bike seems to be extremely (too?) flexible. On two occasions, when making a quick
emergency turn, I've felt it start to whip back and forth in response to the steering. The
whipping motion can be controlled, but it is scary. I can cause the frame to flex in a similar
manner by moving the handlebars abruptly from side to side: the frame flex is enough to be
visible. The bike is a 10-year-old Giant Allegre, made with their own (AFAIK) triple-butted steel
tubing. The question is this: is this 'normal' for a (relatively) light-weight steel frame? Or is
this an unusual (and dangerous) amount of flex, specific to this bike? I would hope to be able to
upgrade to a stiffer frame, probably another steel frame, without spending a fortune, but I want
to be sure that I will be able to eliminate this problem by doing so. Any thoughts?

Thanks

Richard

Richard U? said:

The frame of my bike seems to be extremely (too?) flexible. On two occasions, when making a quick
emergency turn, I've felt it start to whip back and forth in response to the steering. The
whipping motion can be controlled, but it is scary.

By the way, you didn't say when you first noticed this symptom. On the other hand, I am sure you are
imagining this. Frame flex is apparent by a tendency to shimmy as well as not riding in a straight
line when pedaling hard while seated. This was visible on old Alan aluminum frames that had steel
tube size tubes. I can't imagine what your "emergency turn is" since two wheeled vehicles cannot be
steered by turning the bars suddenly as a car. They require countersteer to change direction and
steering angles at any significant speed are notoriously small, unlike when parking a car.

Quoted message said:

I can cause the frame to flex in a similar manner by moving the handlebars abruptly from side to
side: the frame flex is enough to be visible. The bike is a 10-year-old Giant Allegre, made with
their own (AFAIK) triple-butted steel tubing.

You mean the bicycle moves from side to side when you steer it that way? Significant frame flex is
is still so small that you could not discern it while riding. These aren't rubber bands... or a
steel frame getting soft with age.

Quoted message said:

The question is this: is this 'normal' for a (relatively) light-weight steel frame? Or is this an
unusual (and dangerous) amount of flex, specific to this bike?

Your observances are abnormal. How about doing some static tests by standing next to the bicycle and
pushing on the downward pedal sideways. That makes frame elasticity highly visible and can be
qualitatively compared to another bicycle that is believed to be OK.

Quoted message said:

I would hope to be able to upgrade to a stiffer frame, probably another steel frame, without
spending a fortune, but I want to be sure that I will be able to eliminate this problem by doing
so. Any thoughts?

When "would" you do this?

Jobst Brandt [email hidden] Palo Alto CA