Frame Flex on GCN

[cachagua]

Also,

Originally Posted by cachagua

Whether or not frame flex subtracts from your efforts to move the bike forward...

Originally Posted by Kontact

In terms of subtracting from forward movement...

Two very different things here.

[Kontact]

Originally Posted by cachagua

I'm not sure I understand your question... nothing we've been talking about has to do with the freewheel. In fact we could be talking about track bikes, I think the phenomena we want to understand operate the same there. Didn't one of the videos earlier show a track bike?

"Upstream"? You mean, what I've been calling against the direction of drive torque?

Sure. Your choice with a bicycle drivetrain (unlike a lever) is tension or slack. How do you remove tension from the chain when the frame flex is part of the drivetrain? And we know it is part of the drivetrain because it only happens at peak torque.

So given that it is part of the tension driving the bike, how do you tap it off to somewhere else or reverse it in the opposite direction when the opposite direction is slack? Your legs drive the bike, but can't drive you because you can't push a chain.

Originally Posted by cachagua

Two very different things here.

I don't see how they could be. And maybe that's why you conceptualize the tension of your leg muscles as being part of some other system than the tension in the drivetrain.

[kramnnim]

Originally Posted by Kontact

The frame doesn't flex down at 6 o'clock. That's not part of what happens during pedaling and has no place in the discussion.

So...what do you think is happening at 6oclock?

While pedaling in the manner I have described several times already, I firmly believe that the frame is flexed down at 6oclock.

[cachagua]

Dude:

Originally Posted by Kontact

How do you remove tension from the chain when the frame flex is part of the drivetrain?

I have never said the tension is removed from the chain. I have specifically said that doesn't happen, nor is it necessary for what I'm suggesting. See post #109.

Originally Posted by Kontact

How do you reverse it in the opposite direction?

I have never said any part of the bike reverses its motion. I have specifically said that doesn't happen, nor is it necessary for what I'm suggesting. See post #232.

Originally Posted by Kontact

You conceptualize the tension of your leg muscles as being part of some other system than the tension in the drivetrain.

I don't conceptualize anything remotely like that, and I have never said anything at all about your leg muscles.

(I can hardly wait to hear the next thing I didn't say! Did I disprove Goedel's Theorem? Did I kill Jimmy Hoffa? Did I feed the whole city of New York with just a few sardines and a stale bagel? Where is this gonna end!)

If I haven't made my ideas inescapably clear, call it a deficiency in my writing skill. But attributing things to me that I've never said makes it difficult to respond conversationally.

[Kontact]

Originally Posted by kramnnim

So...what do you think is happening at 6oclock?

While pedaling in the manner I have described several times already, I firmly believe that the frame is flexed down at 6oclock.

Bicycle frames are rigid, and will not flex until the strength of the structure is overcome by an unbalanced force great enough to push the structure into elastic deformation. Peak pedaling torque is somewhere around 4 o'clock, and that is where the frame deforms most.

4 o'clock for one pedal is 10 o'clock for the other pedal. Between those two peaks the BB returns to center. Which is about 7 o'clock. These are all ballpark numbers, but the point is that peak flex is when the cranks are level, and zero is the point right between them. You can't get from max on one side to max on the other without going through zero at the bottom.

And we can see on video that the swaying of the BB is regular and smooth, so it doesn't flex, stay there for 90° and then suddenly pop over to the other side and stay there. It oscillates in a very regular sine wave with brief peaks.

[Kontact]

Originally Posted by cachagua

If I haven't made my ideas inescapably clear, call it a deficiency in my writing skill.

I'm not putting words in your mouth, I was trying to follow your objections to their logical conclusions.

But if you have no ideas, then I shouldn't respond as if you do.

[kramnnim]

Originally Posted by Kontact

Bicycle frames are rigid, and will not flex until the strength of the structure is overcome by an unbalanced force great enough to push the structure into elastic deformation. Peak pedaling torque is somewhere around 4 o'clock, and that is where the frame deforms most.

4 o'clock for one pedal is 10 o'clock for the other pedal. Between those two peaks the BB returns to center. Which is about 7 o'clock. These are all ballpark numbers, but the point is that peak flex is when the cranks are level, and zero is the point right between them. You can't get from max on one side to max on the other without going through zero at the bottom.

And we can see on video that the swaying of the BB is regular and smooth, so it doesn't flex, stay there for 90° and then suddenly pop over to the other side and stay there. It oscillates in a very regular sine wave with brief peaks.

When pedaling in the saddle with a good pedaling technique, sure. But that is not what I'm talking about and has never been.

[Mark McM]

Originally Posted by Kontact

Bicycle frames are rigid, and will not flex until the strength of the structure is overcome by an unbalanced force great enough to push the structure into elastic deformation. Peak pedaling torque is somewhere around 4 o'clock, and that is where the frame deforms most.

4 o'clock for one pedal is 10 o'clock for the other pedal. Between those two peaks the BB returns to center. Which is about 7 o'clock. These are all ballpark numbers, but the point is that peak flex is when the cranks are level, and zero is the point right between them. You can't get from max on one side to max on the other without going through zero at the bottom.

And we can see on video that the swaying of the BB is regular and smooth, so it doesn't flex, stay there for 90° and then suddenly pop over to the other side and stay there. It oscillates in a very regular sine wave with brief peaks.

When peak force and deflection occur depends on pedaling style. As you say, in many pedaling styles, particularly when seated, the peak force occurs at 4 o'clock. But when standing, the peak force frequently occurs at 6 o'clock (see the first pedal force diagram I posted earler).

Of course, when standing, the frame is also frequently rocked back and forth, which also raises and lowers the pedals, so the dynamics are a bit more complex. But I still see no reason that the strain energy in the frame can't be returned in some useful way, if the rider has adapted their pedaling style to the frame flex characteristics.

[Kontact]

Originally Posted by kramnnim

When pedaling in the saddle with a good pedaling technique, sure. But that is not what I'm talking about and has never been.

I don't understand why you cachagua feel the need to post what you aren't talking about. If Mark or I could tell what you were talking about the conversation would have likely been wrapped up some time ago.

[kramnnim]

Originally Posted by Kontact

I don't understand why you cachagua feel the need to post what you aren't talking about. If Mark or I could tell what you were talking about the conversation would have likely been wrapped up some time ago.

You're the one responding to stuff other than what we type about.

[kramnnim]

Originally Posted by Mark McM

When peak force and deflection occur depends on pedaling style. As you say, in many pedaling styles, particularly when seated, the peak force occurs at 4 o'clock. But when standing, the peak force frequently occurs at 6 o'clock (see the first pedal force diagram I posted earler).

Of course, when standing, the frame is also frequently rocked back and forth, which also raises and lowers the pedals, so the dynamics are a bit more complex. But I still see no reason that the strain energy in the frame can't be returned in some useful way, if the rider has adapted their pedaling style to the frame flex characteristics.

On the first point- yes, I dug around in the Pioneer data viewing chart and it's clear to see that there is a lot of tangential force at 6oclock, as much as there is radial force at 3oclock.

On the second point- what adaptations would you suggest? Thankfully none of my frames are very flexy, but I do tend to ride like that at times.

[Kontact]

Originally Posted by kramnnim

You're the one responding to stuff other than what we type about.

You don't type about much of anything, you type stuff that either doesn't make sense or just objections to what other people have taken the time to detail.


If you two want to come up with a theory, great. But all you're really doing is posting "I don't think so" over and over.

[kramnnim]

Originally Posted by Kontact

You don't type about much of anything, you type stuff that either doesn't make sense or just objections to what other people have taken the time to detail.


If you two want to come up with a theory, great. But all you're really doing is posting "I don't think so" over and over.

So you just skim over stuff, cool.

In the pedaling situation that I keep mentioning, where the rider is out of the saddle, rocking the bike with his or her arms, 60rpm or so- I think the frame flexes between 2 and 5 oclock, taking torque/rotational force from the rider. The frame flexes back at 6 oclock, and I don't think it helps the crank arm rotate. Sure, the riders foot may go upwards, but it took away a fraction of a degree of rotation, and did not give it back. So I think that energy was wasted.

...I tested this for myself yesterday with a Pioneer power meter+head unit and there's no force shown at 7 oclock. At 8, it shows me pulling up.

I'm objecting to the claim that energy spent flexing a flexy frame will eventually help to propel the rider, as suggested by the GCN video. I don't think this is true when riding out of the saddle/low rpm/rocking the bike. (which is when I personally have noticed frame flex) (Side note, after looking more at Pioneer data, I believe the flex changes direction when the cranks are around 1 and 7 oclock...not at 12 and 6)

[Kontact]

Originally Posted by kramnnim

I'm objecting to the claim that energy spent flexing a flexy frame will eventually help to propel the rider, as suggested by the GCN video. I don't think this is true when riding out of the saddle/low rpm/rocking the bike. (which is when I personally have noticed frame flex) (Side note, after looking more at Pioneer data, I believe the flex changes direction when the cranks are around 1 and 7 oclock...not at 12 and 6)

You don't think, but you never propose what you do think. Cool.

Originally Posted by Kontact

Between those two peaks the BB returns to center. Which is about 7 o'clock.

[kramnnim]

Originally Posted by Kontact

You don't think, but you never propose what you do think. Cool.

I think a flexy frame wastes energy under certain pedaling styles.