Frame flex and efficiency



"jim beam" <[email protected]> wrote in message
news:[email protected]...
> [email protected] wrote:
>> Jobst Brandt
>
> in summary:
>
> "frame flex ... is so small ... riding behind the first ... 753 frames
> showed me a squirrelly line"
>
> so is frame flex ignorable or not? [rhetorical] in typical jobstian
> style, it seems that it's ignorable if it's inconvenient to your argument
> but relevant & responsible for significant behavior characteristics only
> if it is convenient - as per the latest shimmy thread.
>
Do you have to go after everything that he posts? You better watch out or
the stalker unit might be at your door soon.
 
On Fri, 5 Aug 2005 20:05:25 -0700, "Frank Drackman"
<[email protected]> wrote:

>
>"jim beam" <[email protected]> wrote in message
>news:[email protected]...
>> [email protected] wrote:
>>> Jobst Brandt
>>
>> in summary:
>>
>> "frame flex ... is so small ... riding behind the first ... 753 frames
>> showed me a squirrelly line"
>>
>> so is frame flex ignorable or not? [rhetorical] in typical jobstian
>> style, it seems that it's ignorable if it's inconvenient to your argument
>> but relevant & responsible for significant behavior characteristics only
>> if it is convenient - as per the latest shimmy thread.
>>
>Do you have to go after everything that he posts? You better watch out or
>the stalker unit might be at your door soon.
>

Dear Frank,

Jim and Jobst often disagree.

In this case, Jim does seem to be making a worthwhile point.

Jobst began by saying that frame flex is too small to be
addressed:

"Most of this frame flex that gets so much attention is so
small that it is hard to prove anything about it."

But in his very next paragraph Jobst wrote that the effect
of frame flex was so obvious that he could see it at work
from behind another bicyclist:

" . . . riding behind the first Raleigh Reynolds 753 frames
showed me a squirrelly line similar to that of an Alan
aluminum bicycle."

Obviously, if Jobst could see the effect of frame flex while
riding behind someone else, it should be easy to prove
something about it.

To be fair to Jobst, he may have meant to distinguish
between any power losses and the squirrelly handling
problems of rame flex--but instead of making the
distinction, he apparently contradicted himself rather
strikingly.

To be fair to Jim, imagine what Jobst would have written if
anyone else proclaimed that something was "so small that it
is hard to prove anything about it" and then wandered down
memory lane to recall how obvious its effect was?

Carl Fogel
 
<[email protected]> wrote in message
news:[email protected]...
> On Fri, 5 Aug 2005 20:05:25 -0700, "Frank Drackman"
> <[email protected]> wrote:
>
>>
>>"jim beam" <[email protected]> wrote in message
>>news:[email protected]...
>>> [email protected] wrote:
>>>> Jobst Brandt
>>>
>>> in summary:
>>>
>>> "frame flex ... is so small ... riding behind the first ... 753
>>> frames
>>> showed me a squirrelly line"
>>>
>>> so is frame flex ignorable or not? [rhetorical] in typical
>>> jobstian
>>> style, it seems that it's ignorable if it's inconvenient to your
>>> argument
>>> but relevant & responsible for significant behavior characteristics
>>> only
>>> if it is convenient - as per the latest shimmy thread.
>>>
>>Do you have to go after everything that he posts? You better watch
>>out or
>>the stalker unit might be at your door soon.
>>
>
> Dear Frank,
>
> Jim and Jobst often disagree.
>
> In this case, Jim does seem to be making a worthwhile point.
>
> Jobst began by saying that frame flex is too small to be
> addressed:
>
> "Most of this frame flex that gets so much attention is so
> small that it is hard to prove anything about it."
>
> But in his very next paragraph Jobst wrote that the effect
> of frame flex was so obvious that he could see it at work
> from behind another bicyclist:
>
> " . . . riding behind the first Raleigh Reynolds 753 frames
> showed me a squirrelly line similar to that of an Alan
> aluminum bicycle."
>
> Obviously, if Jobst could see the effect of frame flex while
> riding behind someone else, it should be easy to prove
> something about it.
>
> To be fair to Jobst, he may have meant to distinguish
> between any power losses and the squirrelly handling
> problems of rame flex--but instead of making the
> distinction, he apparently contradicted himself rather
> strikingly.
>
> To be fair to Jim, imagine what Jobst would have written if
> anyone else proclaimed that something was "so small that it
> is hard to prove anything about it" and then wandered down
> memory lane to recall how obvious its effect was?
>
Context is everything. When it comes to energy loss it is small even if
the flex is observable. It is also insignificant when it comes to
comfort. It has more of an effect on handling and obviously is a huge
factor in shimmy. At the risk of appearing to be "kissing ass", I have
never heard Jobst detract from these characteristics.

Phil H
 
<[email protected]> wrote in message
news:[email protected]...
> On Fri, 5 Aug 2005 20:05:25 -0700, "Frank Drackman"
> <[email protected]> wrote:
>
>>
>
> Dear Frank,
>
> Jim and Jobst often disagree.
>
> In this case, Jim does seem to be making a worthwhile point.
>

I didn't make any claim about the validity of Jim's post, only that it seems
to me he scans every post that Jobst makes looking for errors then attacks
him. It just seems so silly to me. Like a little kid saying that my father
can beat your father up.
 
Frank Drackman wrote:
> <[email protected]> wrote in message
> news:[email protected]...
>
>>On Fri, 5 Aug 2005 20:05:25 -0700, "Frank Drackman"
>><[email protected]> wrote:
>>
>>
>>Dear Frank,
>>
>>Jim and Jobst often disagree.
>>
>>In this case, Jim does seem to be making a worthwhile point.
>>
>
>
> I didn't make any claim about the validity of Jim's post, only that it seems
> to me he scans every post that Jobst makes looking for errors then attacks
> him. It just seems so silly to me. Like a little kid saying that my father
> can beat your father up.
>
>
i'm interested in shimmy because it caused me an accident where i
cracked a hip & couldn't walk without pain for a full 12 months. the
solution to shimmy is simple and obvious, but our resident "expert"

1. doesn't see the problem
2. doesn't understand the problem, &
3. doesn't care to fix the problem.

if seeking faq revision to reflect reality and solution is "silly" to
you, then sure, silliness will continue.
 
[email protected] wrote:
> As far as it goes, I can see that energy stored in the frame would to a
> large degree be returned to the drive train. The rotation of the pedal
> that is allowed by frame flex causes me some concern. On a flexible
> frame under heavy load the outside of the pedal drops in relation to
> the inside, allowing the foot to twist and apply lateral stress to the
> knee. I seems to me that those, like me, missing full ligament
> support would have problems.
>
> Wayne
>
I actually had a different issue with my first two alu frames, the Vitus
frame with hexagonal tubing on the down and seat tubes was wispy under
power but superbe on hills (go figure), the only hassle was that the
frame flex caused the front derailleur to derail repeatedly. The
Cannondale was stiff as all hell and I couldn't feel the give then take
that the Vitus had imparted to my pedalling motion, on hills the
Cannondale felt dead.
I miss the Vitus, it deconstructed itself at the crest of a very long
downhill, just one slippery pedal stroke too much. Thankfully not
halfway down the hill at 60km+. The replacement bike, the Cannondale,
was a disappointment after the performance in races of the Vitus.
As to physical issues, the Vitus was never a burden on my knees. More
you could say that this flexible frame imparted a fluid motion to my
pedalling and I had to relearn pedalling on the next, replacement frame.
 
Philip Holman wrote:

> Methink Jim B has an agenda when it comes to Jobst.

Really?! And he kept it so well hidden!u
 
Frank Drackman wrote:

> I didn't make any claim about the validity of Jim's post, only that it seems
> to me he scans every post that Jobst makes looking for errors then attacks
> him. It just seems so silly to me.

Yeah, but don't forget Carl does the same thing too. "Looking for
errors" is too generous though, they are just looking for an
opportunity to diss, and are just as happy to manufacture
contradictions themselves:m
 
[email protected] wrote:

> Jobst began by saying that frame flex is too small to be
> addressed:
>
> "Most of this frame flex that gets so much attention is so
> small that it is hard to prove anything about it."
>
> But in his very next paragraph Jobst wrote that the effect
> of frame flex was so obvious that he could see it at work
> from behind another bicyclist:

Dude, try buying a dictionary and looking up "most".

> " . . . riding behind the first Raleigh Reynolds 753 frames
> showed me a squirrelly line similar to that of an Alan
> aluminum bicycle."

> To be fair to Jobst, he may have meant to distinguish
> between any power losses and the squirrelly handling
> problems of rame flex--

Yeah, he may have meant to in the very next two sentences that you so
thoughtfully deleted, because you love being fair:

"I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control."

> but instead of making the
> distinction, he apparently contradicted himself rather
> strikingly.

Seriously man. What drugs are you doing? Your dealer must be cutting
with something baaad. Call the FDA, call your shrink, call somebody,
because you are going blind. That's not being fair, that's being
charitable.



t
 
"41" <[email protected]> wrote in message
news:[email protected]...
>
> Philip Holman wrote:
>
>> Methink Jim B has an agenda when it comes to Jobst.
>
> Really?! And he kept it so well hidden!u
>
Almost as well hidden as your sarcasm :)

Phil H
 
[email protected] wrote:
> Do you have any rough estimate of how much this side-to-side
> wriggling of the tires would be on a more flexible frame,
> compared to a stiff frame? Is it something like an inch or
> two to either side?
>
In figure 6 of the first article I linked to, they show a wire drawing
of a Vitus frame at the highest force condition with deflections
magnified 7.5x. It is difficult to tell, but it looks like the rear
axle is about 0.6 inches out of a vertical plane that goes through the
headtube and bottom bracket.

> It would be nice if someone with a wriggly frame and a stiff
> frame could lure an unsuspecting tester into rolling through
> a puddle right at the bottom of a steep climb and see how
> the tire tracks compare.

The wriggly frame would have to travel slightly farther at least... but
I'm still wondering if tire scrub might be the biggest factor.

-Ron
 
[email protected] wrote:

> I take it that you've observed the more flexible frame's
> "squirrelly line" that Jobst mentions.

Yes--on a bike I was riding, not watching someone else.

> If this is during straight-forward climbing, wouldn't all
> that side-to-side motion require a fair amount of force?

I had to be pushing hard to notice it.

> I understand that there's the notion of a nearly perfect
> spring that somehow usefully returns all the energy put into
> it, but now you and Jobst have me thinking that the metal
> frame's flex is causing the bike and its tires to snake up
> the hill, which doesn't sound at all like perfect springing.

Whether the frame returns the energy it stores (exhibits
negligible hysteretic loss, as Jobst might say) is a
different question than whether the energy it returns
is wasted somewhere else. I was commenting on losses
elsewhere, not in the frame itself.

> Do you have any rough estimate of how much this side-to-side
> wriggling of the tires would be on a more flexible frame,
> compared to a stiff frame? Is it something like an inch or
> two to either side?

I don't have a sense of scale like that, no. I just had
a sense of the bike squirming around.

> It would be nice if someone with a wriggly frame and a stiff
> frame could lure an unsuspecting tester into rolling through
> a puddle right at the bottom of a steep climb and see how
> the tire tracks compare.

I agree; that would be interesting.

Tom Ace
 
On 6 Aug 2005 14:04:11 -0700, "Ron Ruff"
<[email protected]> wrote:

>[email protected] wrote:
>> Do you have any rough estimate of how much this side-to-side
>> wriggling of the tires would be on a more flexible frame,
>> compared to a stiff frame? Is it something like an inch or
>> two to either side?
>>
>In figure 6 of the first article I linked to, they show a wire drawing
>of a Vitus frame at the highest force condition with deflections
>magnified 7.5x. It is difficult to tell, but it looks like the rear
>axle is about 0.6 inches out of a vertical plane that goes through the
>headtube and bottom bracket.
>
>> It would be nice if someone with a wriggly frame and a stiff
>> frame could lure an unsuspecting tester into rolling through
>> a puddle right at the bottom of a steep climb and see how
>> the tire tracks compare.
>
>The wriggly frame would have to travel slightly farther at least... but
>I'm still wondering if tire scrub might be the biggest factor.
>
>-Ron

Dear Ron,

That would be this site:

http://www.bikethink.com/Frameflex.htm

I'm not sure which figure you have in mind, but I do
remember seeing the 7.5x figure somewhere.

I get horribly confused when I look at the diagrams, but I
think that this may be the side-to-side one:

http://www.bikethink.com/beam_corr.htm

The link above is to some sort of comparison between the FEA
model and Damon Rinard's load testing.

I think that it's giving the predicted sideways bend one way
for the front and rear triangles at the axle over the
contact patch.

If so, the front deflects more than twice as much as the
well-braced rear.

If the load involved is plausible, then the front axle moves
about 9-10 mm to the side, while the rear axle moves about
3-4 mm, then back to the center, and then the other way just
as much.

If the front wheel is moving back and forth 18 mm relative
to an idealized straight line as viewed by Jobst and Tom, I
think that the wiggle that they're talking about should
indeed be visible. Even the rear wheel's reduced wiggle of
about 7-8 mm would be noticeable to a rider close behind.

Thanks for reminding me to look at your earlier post and the
nice link.

Carl Fogel
 
On 7 Aug 2005 01:02:55 -0700, "Ron Ruff"
<[email protected]> wrote:

>[email protected] wrote:
>>
>> Dear Ron,
>>
>> That would be this site:
>>
>> http://www.bikethink.com/Frameflex.htm
>>
>Actually I was refering to the article on Sheldon's site, but...
>> http://www.bikethink.com/beam_corr.htm
>>
>Thanks for pointing that out... that is much easier to make sense of!
>
>-Ron

Dear Ron,

Aaargh!

Sorry.

A smarter reader might have figured out what you meant when
you wrote "the first article that I linked to."

Carl Fogel
 
[email protected] wrote:

> > In the demonstration I described, the pedal gets closer to the
> > ground (most noticeably at its outermost point). It's not like BB
> > displacement is the only thing going on; there's torsion as well.
>
> How much? How about measuring it. I think you'll find it is tiny.
> Of course you need to restrain the bicycle so you are measuring the
> right thing and not just leaning the bicycle.

In the stationary-bike demonstration, I can lower the outside
of the left pedal by about one inch. This is with a Columbus SL
frame (from the late 1970s) and 170mm cranks, and I weigh 85kg.

Tom Ace
 
Tom Ace <[email protected]> writes:

>>> In the demonstration I described, the pedal gets closer to the
>>> ground (most noticeably at its outermost point). It's not like BB
>>> displacement is the only thing going on; there's torsion as well.

>> How much? How about measuring it. I think you'll find it is tiny.
>> Of course you need to restrain the bicycle so you are measuring the
>> right thing and not just leaning the bicycle.

> In the stationary-bike demonstration, I can lower the outside of the
> left pedal by about one inch. This is with a Columbus SL frame
> (from the late 1970s) and 170mm cranks, and I weigh 85kg.

That's substantial. My bicycle does not produce such deflections when
I am climbing. I don't know what it did when I rode up Filbert Street SF.

Jobst Brandt
 
On 7 Aug 2005 21:43:41 -0700, "Tom Ace" <[email protected]>
wrote:

>[email protected] wrote:
>
>> > In the demonstration I described, the pedal gets closer to the
>> > ground (most noticeably at its outermost point). It's not like BB
>> > displacement is the only thing going on; there's torsion as well.
>>
>> How much? How about measuring it. I think you'll find it is tiny.
>> Of course you need to restrain the bicycle so you are measuring the
>> right thing and not just leaning the bicycle.
>
>In the stationary-bike demonstration, I can lower the outside
>of the left pedal by about one inch. This is with a Columbus SL
>frame (from the late 1970s) and 170mm cranks, and I weigh 85kg.
>
>Tom Ace

Dear Tom,

Does this drop take into account the flattening of the tires
with the load?

Carl Fogel
 
[email protected] wrote:

> >In the stationary-bike demonstration, I can lower the outside
> >of the left pedal by about one inch. This is with a Columbus SL
> >frame (from the late 1970s) and 170mm cranks, and I weigh 85kg.

> Does this drop take into account the flattening of the tires
> with the load?

The one inch doesn't include the tire squashage.
The pedal drops by a little over an inch relative to the floor.

Tom Ace
 
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