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