Frame flex and efficiency

kerank said:

I'm curious as to other peoples thoughts on this. The "flex" I am
talking about is (I think) bottom-bracket flex. It's most noticable
when cranking up a steep grade, or sprinting. I have two bikes, and
one of them has more flex than the other. However, if I am not trying
to accelerate quickly, I actually "feel" faster on the more flexible
bike. It feels easier to maintain a high pace on the more flexible
bike.... almost like I'm using less energy to maintain a certain pace
compared to the more stiff bike.

I've read where a more flexible bike will act like a spring and return
some energy to the opposite pedal stroke. Is there any truth to this?
Any data to back it up?

I feel faster on a stiffer bike, but I'm sure it's all in both of our
heads. The usual argument is that stiff frames accelerate more
"efficiently" -- but that's likely just wishful thinking.

A perfect spring has no losses. I think a bike frame is pretty close to
a perfect spring, if it wasn't, there'd be a lot more attention given to
frame flex.

Flexible frames are less stable at high speed though, that's something I
notice right away since I ride 68cm frames. I really don't care for the
feel of my steel framed bikes at speeds over 40, they don't shimmy, just
ride a little "vague". Since I don't spend much time at those speeds
I don't worry about it.

Peter Cole said:

Quoted message said:

I'm curious as to other peoples thoughts on this. The "flex" I am
talking about is (I think) bottom-bracket flex. It's most
noticable when cranking up a steep grade, or sprinting. I have two
bikes, and one of them has more flex than the other. However, if I
am not trying to accelerate quickly, I actually "feel" faster on
the more flexible bike. It feels easier to maintain a high pace on
the more flexible bike.... almost like I'm using less energy to
maintain a certain pace compared to the more stiff bike.

Quoted message said:

Quoted message said:

I've read where a more flexible bike will act like a spring and
return some energy to the opposite pedal stroke. Is there any
truth to this? Any data to back it up?

Quoted message said:

I feel faster on a stiffer bike, but I'm sure it's all in both of
our heads. The usual argument is that stiff frames accelerate more
"efficiently" -- but that's likely just wishful thinking.

Quoted message said:

A perfect spring has no losses. I think a bike frame is pretty close
to a perfect spring, if it wasn't, there'd be a lot more attention
given to frame flex.

Most of this frame flex that gets so much attention is so small that
it is hard to prove anything about it. Vertically (in the plane of
the wheels) bicycles have effectively no flex. The flex that shows up
is seen when standing and pushing the BB side to side. This is a cosine
and has little effect on muscular extension.

Where this all becomes more obvious is on suspension bicycle where
springiness interferes with propulsion. Besides that, it has shock
absorbers that take a bit of energy out of the pedaling cycle.
Therefore the better bicycles have suspension lockout. Road bicycles
without significant vertical compliance don't need this but their
torsional rigidity has an effect on descending and shimmy.

Quoted message said:

Flexible frames are less stable at high speed though, that's
something I notice right away since I ride 68cm frames. I really
don't care for the feel of my steel framed bikes at speeds over 40,
they don't shimmy, just ride a little "vague". Since I don't spend
much time at those speeds I don't worry about it.

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan aluminum
bicycle. I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control.

Jobst Brandt

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Peter Cole said:

Quoted message said:

I'm curious as to other peoples thoughts on this. The "flex" I am
talking about is (I think) bottom-bracket flex. It's most
noticable when cranking up a steep grade, or sprinting. I have two
bikes, and one of them has more flex than the other. However, if I
am not trying to accelerate quickly, I actually "feel" faster on
the more flexible bike. It feels easier to maintain a high pace on
the more flexible bike.... almost like I'm using less energy to
maintain a certain pace compared to the more stiff bike.

Quoted message said:

Quoted message said:

I've read where a more flexible bike will act like a spring and
return some energy to the opposite pedal stroke. Is there any
truth to this? Any data to back it up?

Quoted message said:

I feel faster on a stiffer bike, but I'm sure it's all in both of
our heads. The usual argument is that stiff frames accelerate more
"efficiently" -- but that's likely just wishful thinking.

Quoted message said:

A perfect spring has no losses. I think a bike frame is pretty close
to a perfect spring, if it wasn't, there'd be a lot more attention
given to frame flex.

Most of this frame flex that gets so much attention is so small that
it is hard to prove anything about it. Vertically (in the plane of
the wheels) bicycles have effectively no flex. The flex that shows up
is seen when standing and pushing the BB side to side. This is a cosine
and has little effect on muscular extension.

Where this all becomes more obvious is on suspension bicycle where
springiness interferes with propulsion. Besides that, it has shock
absorbers that take a bit of energy out of the pedaling cycle.
Therefore the better bicycles have suspension lockout. Road bicycles
without significant vertical compliance don't need this but their
torsional rigidity has an effect on descending and shimmy.

Quoted message said:

Flexible frames are less stable at high speed though, that's
something I notice right away since I ride 68cm frames. I really
don't care for the feel of my steel framed bikes at speeds over 40,
they don't shimmy, just ride a little "vague". Since I don't spend
much time at those speeds I don't worry about it.

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan aluminum
bicycle. I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control.

For those interested in that kind of thing, the Australian magazine 'Ride'
now has a bike testing jig, and measures deflexion at the BB, head tube and
seat tube junctions when a moment is applied to the BB. Mag comes out
quarterly.

Cheers
Gemma

Dans le message de news:[email hidden],
Gemma_k <[email hidden]> a réfléchi, et puis a
déclaré :

Quoted message said:

For those interested in that kind of thing, the Australian magazine
'Ride' now has a bike testing jig, and measures deflexion at the BB,
head tube and seat tube junctions when a moment is applied to the BB.
Mag comes out quarterly.

Cheers
Gemma

Gemma - forget it with Mr Brandt. I sent him a series of tests of frame
flex, original cuts from the magazine Le Cycle, and he still talks from the
seat of his pants. Facts would just confuse the artistry of his replies.
--
Sandy
Verneuil-sur-Seine
*******

La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.

Quoted message said:

Quoted message said:

This is a cosine

and has little effect on muscular extension.
<<

Can you elaborate on what that statement means?

Thanks,
John

Sandy,

I'd be interested in these tests of frame flex. Do you happen to know
if I
can find the articles online?

Merci beaucoup,
John

Dans le message de
news:[email hidden],
JS <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy,

I'd be interested in these tests of frame flex. Do you happen to know
if I
can find the articles online?

Merci beaucoup,
John

Not that I know of.

"JS" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

Quoted message said:

This is a cosine

and has little effect on muscular extension.
<<

Can you elaborate on what that statement means?

It means that the lateral flex translates to a very small amount of for
and aft flex.

Phil H

"Sandy" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Dans le message de
news:[email hidden],
JS <[email hidden]> a réfléchi, et puis a déclaré :

Quoted message said:

Sandy,

I'd be interested in these tests of frame flex. Do you happen to
know
if I
can find the articles online?

Merci beaucoup,
John

Not that I know of.

Do you remember what the conclusion of their article was with regards to
energy loss?

Phil H

Sandy said:

Dans le message de news:[email hidden],
Gemma_k <[email hidden]> a réfléchi, et puis a
déclaré :

Quoted message said:

For those interested in that kind of thing, the Australian magazine
'Ride' now has a bike testing jig, and measures deflexion at the BB,
head tube and seat tube junctions when a moment is applied to the BB.
Mag comes out quarterly.

Cheers
Gemma

Gemma - forget it with Mr Brandt. I sent him a series of tests of frame
flex, original cuts from the magazine Le Cycle, and he still talks from the
seat of his pants. Facts would just confuse the artistry of his replies.

where can i get this magazine here in the u.s?

Quoted message said:

Do you remember what the conclusion of their article was with regards to
energy loss?

Phil H

I suppose the efficiency of different frames would be quite easy to measure
with the power tap or corresponding equipment. But as no-one seems to be
marketing their frames as "measured to be more efficient", I doubt that the
possible differences in energy losses are not visible at all.

Antti

Quoted message said:

Peter Cole said:

Quoted message said:

I'm curious as to other peoples thoughts on this. The "flex" I am
talking about is (I think) bottom-bracket flex. It's most
noticable when cranking up a steep grade, or sprinting. I have two
bikes, and one of them has more flex than the other. However, if I
am not trying to accelerate quickly, I actually "feel" faster on
the more flexible bike. It feels easier to maintain a high pace on
the more flexible bike.... almost like I'm using less energy to
maintain a certain pace compared to the more stiff bike.

Quoted message said:

Quoted message said:

I've read where a more flexible bike will act like a spring and
return some energy to the opposite pedal stroke. Is there any
truth to this? Any data to back it up?

Quoted message said:

I feel faster on a stiffer bike, but I'm sure it's all in both of
our heads. The usual argument is that stiff frames accelerate more
"efficiently" -- but that's likely just wishful thinking.

Quoted message said:

A perfect spring has no losses. I think a bike frame is pretty close
to a perfect spring, if it wasn't, there'd be a lot more attention
given to frame flex.

Most of this frame flex that gets so much attention is so small that
it is hard to prove anything about it. Vertically (in the plane of
the wheels) bicycles have effectively no flex. The flex that shows up
is seen when standing and pushing the BB side to side. This is a cosine
and has little effect on muscular extension.

Where this all becomes more obvious is on suspension bicycle where
springiness interferes with propulsion. Besides that, it has shock
absorbers that take a bit of energy out of the pedaling cycle.
Therefore the better bicycles have suspension lockout. Road bicycles
without significant vertical compliance don't need this but their
torsional rigidity has an effect on descending and shimmy.

Quoted message said:

Flexible frames are less stable at high speed though, that's
something I notice right away since I ride 68cm frames. I really
don't care for the feel of my steel framed bikes at speeds over 40,
they don't shimmy, just ride a little "vague". Since I don't spend
much time at those speeds I don't worry about it.

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan aluminum
bicycle. I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control.

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.

jim beam said:

Sandy said:

Dans le message de news:[email hidden],
Gemma_k <[email hidden]> a réfléchi, et puis a
déclaré :

Quoted message said:

For those interested in that kind of thing, the Australian magazine
'Ride' now has a bike testing jig, and measures deflexion at the BB,
head tube and seat tube junctions when a moment is applied to the BB.
Mag comes out quarterly.

Cheers
Gemma

Gemma - forget it with Mr Brandt. I sent him a series of tests of frame
flex, original cuts from the magazine Le Cycle, and he still talks from the
seat of his pants. Facts would just confuse the artistry of his replies.

where can i get this magazine here in the u.s?

Dear Jim,

Ride Magazine from Australia to U.S., 4 issues ~$57.72 US:

http://shop.cyclingnews.com.au/Cyclingnews/catalogue/category2/product2

Le Cycle from France to U.S., $82.20 US for 11 issues:

http://www.amazon.com/exec/obidos/ASIN/B00006LBRP/dealtime-magazines-feed-20/002-3782235-2728826

For single issues, you could try a library search, visit a
large San Francisco newsstand-style bookstore, impose on
friends travelling that way (my favorite tactic), or try
emailing Bob at the site below--he's always been helpful to
me and might mail you a single Oz magazine:

http://www.bookworm.com.au/cgi-bin/bookmall/bookworm/index.tam

Carl Fogel

jim beam said:

Quoted message said:

Most of this frame flex that g ets so much attention is so small that
it is hard to prove anything about it. Vertically (in the plane of
the wheels) bicycles have effectively no flex. The flex that shows up
is seen when standing and pushing the BB side to side. This is a cosine
and has little effect on muscular extension.

[...]

Quoted message said:

Quoted message said:

torsional rigidity has an effect on descending and shimmy.

Quoted message said:

Quoted message said:

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan aluminum
bicycle. I think that is where the rea sonable flex limit is most
apparent. It has less to do with power loss than control.

Jobst Brandt

in summary:

"frame flex ... is so small ... riding behind the first ... 753 frames
showed me a squirrelly line"

so is frame f lex 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.

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.

Quoted message said:

jim beam said:

Sandy said:

Dans le message de news:[email hidden],
Gemma_k <[email hidden]> a réfléchi, et puis a
déclaré :

>For those interested in that kind of thing, the Australian magazine
>'Ride' now has a bike testing jig, and measures deflexion at the BB,
>head tube and seat tube junctions when a moment is applied to the BB.
>Mag comes out quarterly.
>
>Cheers
>Gemma

Gemma - forget it with Mr Brandt. I sent him a series of tests of frame
flex, original cuts from the magazine Le Cycle, and he still talks from the
seat of his pants. Facts would just confuse the artistry of his replies.

where can i get this magazine here in the u.s?

Dear Jim,

Ride Magazine from Australia to U.S., 4 issues ~$57.72 US:

http://shop.cyclingnews.com.au/Cyclingnews/catalogue/category2/product2

Le Cycle from France to U.S., $82.20 US for 11 issues:

http://www.amazon.com/exec/obidos/ASIN/B00006LBRP/dealtime-magazines-feed-20/002-3782235-2728826

For single issues, you could try a library search, visit a
large San Francisco newsstand-style bookstore, impose on
friends travelling that way (my favorite tactic), or try
emailing Bob at the site below--he's always been helpful to
me and might mail you a single Oz magazine:

http://www.bookworm.com.au/cgi-bin/bookmall/bookworm/index.tam

Carl Fogel

thanks carl!

jim beam said:

Quoted message said:

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan aluminum
bicycle. I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control.

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.

He said frame flex affects control but not power. That was clear enough
to me.

--
Tom Reingold
Noo Joizy
This email address works, but only for a short time.

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

"Tom Reingold" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

jim beam said:

Quoted message said:

As I have mentioned, riding behind the first Raleigh Reynolds 753
frames showed me a squirrelly line similar to that of an Alan
aluminum
bicycle. I think that is where the reasonable flex limit is most
apparent. It has less to do with power loss than control.

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.

He said frame flex affects control but not power. That was clear
enough to me.

We've thrashed this to death before. Power loss is microscopic,
handling becomes an issue if lateral frame flex to too large. What I've
speculated in the past is that the head tube moves out of plane with the
seat tube. This in turn means the rear wheel does not track with the
front and when powering around a corner, handling is a problem.
I have an old steel pursuit bike with aero tubing that rides fine in
a straight line but crabs its way around a bend on the track. It is
almost unrideable above 32mph. At the other extreme I had a Trek carbon
fiber team bike that was fairly stiff and tracked like it was on rails.
Methink Jim B has an agenda when it comes to Jobst.

Phil H

Quoted message said:

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.

How far does a leg flex, even a very healthy one?

In any case I'm sure frame flex is not a problem in that way.

Ron