First attempt with SPD's today in 30 mins

RealMan

supersonic wrote:

bike-a-swan wrote:

That's my point. If you had no weight, could you power a rotating system? If you pushed on something unrestrained you'd float away. If you pushed on something with one hand and pulled with the other, you wouldn't move because the net force would be zero. However, if you add a distance between the action points, there will be a torque around some central position, surely?

If you were stood on the pedals I don't think you could turn the cranks.

If you were strapped to the bike, then yes.

Of course you could lol.

supersonic wrote:

Downward and upward doesn't exist in circular motion. Only clockwise and anti clockwise. Both pedals are going in the same direction.

But we have been talking about the direction of forces, which are important.

Yes, and the direction is always clockwise (from the drive side).

bike-a-swan

That's interesting, I think I may have to respectfully disagree with you there for the moment. Whichever way you resolve the forces I can't see it not working. That said, I'm only doing it in my head. The problem with mine is that you'd need to be able resist the reaction in rotation, but I don't think it's unreasonable to allow the handlebars for this for the purpose of this idea. Put it this way, could you open a screw top bottle in space?

RealMan

If you weren't holding on to the bottle, yes, but it would be hard.

But that's a different situation.

Cferg

bike-a-swan wrote:

Put it this way, could you open a screw top bottle in space?

I don't see why not?

RealMan

Cferg I think he's referring to a situation where the bottle is attached to the wall or floor at its base, and you're floating in the air, trying to unscrew it with one hand.

I think.

bike-a-swan

RealMan wrote:

If you weren't holding on to the bottle, yes, but it would be hard.

But that's a different situation.

Ah, I was disagreeing with super. Just took me a while. If the bottle was clamped, could you rotate the lid? If yes, you must be able to apply torque without the need for a linear reaction (rotational, yes, linear no).

bike-a-swan

RealMan wrote:

Cferg I think he's referring to a situation where the bottle is attached to the wall or floor at its base, and you're floating in the air, trying to unscrew it with one hand.

I think.

Yeah. One hand, or two hands, makes no difference. Assuming you're still applying a torque where the magnitudes of the forces acting were the same.

RealMan

You could, if you spun it hard and fast, it would unscrew. Imagine hanging from a wheel (like a hatch on a submarine). If you jerked at the wheel, it would turn and come open eventually.

Aidy

supersonic wrote:

There is no need to keep linking to STW.

But one post stands out:

'It's about frames of reference and what the people are pulling and pushing against, that's what's complicating the thought process I think.'

Downward and upward doesn't exist in circular motion. Only clockwise and anti clockwise. Both pedals are going in the same direction.

But we have been talking about the direction of forces, which are important.

You should be talking about moments, rather than vertical forces.

You might push down on the pedal, but you don't sink into the ground do you?
What makes you think that pulling up on the opposite pedal should cancel out forwards motion?

supersonic

RealMan wrote:

supersonic wrote:

bike-a-swan wrote:

That's my point. If you had no weight, could you power a rotating system? If you pushed on something unrestrained you'd float away. If you pushed on something with one hand and pulled with the other, you wouldn't move because the net force would be zero. However, if you add a distance between the action points, there will be a torque around some central position, surely?

If you were stood on the pedals I don't think you could turn the cranks.

If you were strapped to the bike, then yes.

Of course you could lol.

supersonic wrote:

Downward and upward doesn't exist in circular motion. Only clockwise and anti clockwise. Both pedals are going in the same direction.

But we have been talking about the direction of forces, which are important.

Yes, and the direction is always clockwise (from the drive side).

And they are not braced or strapped? Of course they are.

The applied force varies throughout the pedal stroke.

supersonic

Aidy wrote:

supersonic wrote:

There is no need to keep linking to STW.

But one post stands out:

'It's about frames of reference and what the people are pulling and pushing against, that's what's complicating the thought process I think.'

Downward and upward doesn't exist in circular motion. Only clockwise and anti clockwise. Both pedals are going in the same direction.

But we have been talking about the direction of forces, which are important.

You should be talking about moments, rather than vertical forces.

You might push down on the pedal, but you don't sink into the ground do you?
What makes you think that pulling up on the opposite pedal should cancel out forwards motion?

I have never said anywhere that it cancels out forward motion. Nowhere at all.

bike-a-swan

RealMan wrote:

You could, if you spun it hard and fast, it would unscrew. Imagine hanging from a wheel (like a hatch on a submarine). If you jerked at the wheel, it would turn and come open eventually.

Not quite what I was getting at, but yes. The rate at which you do it isn't really important here. If you weren't constrained in rotation on the same axis, you would just begin to spin in the opposite direction at an angular velocity dependent on your rotational inertia around that axis. It would not, however, cause you to move location. This leads me to think that you could pedal in zero g if clipped in, which in turn suggests to me that you could apply more force to your pedals than your weight. Can anyone spot any serious problems with the logic? I can't see anything yet.

Aidy

supersonic wrote:

Aidy wrote:

You should be talking about moments, rather than vertical forces.

You might push down on the pedal, but you don't sink into the ground do you?
What makes you think that pulling up on the opposite pedal should cancel out forwards motion?

I have never said anywhere that it cancels out forward motion. Nowhere at all.

Apologies, skimmed posts too quickly and mixed a few people up.

Slightly boggling that some people think that because you pull up on one pedal, it cancels out the pushing down force on the other.

RealMan

Aidy wrote:

Slightly boggling that some people think that because you pull up on one pedal, it cancels out the pushing down force on the other.

I know, how do you explain that the grass is in fact green when people insist its red? Its crazy.

Oxygen Thief

Aidy wrote:

supersonic wrote:

Aidy wrote:

You should be talking about moments, rather than vertical forces.

You might push down on the pedal, but you don't sink into the ground do you?
What makes you think that pulling up on the opposite pedal should cancel out forwards motion?

I have never said anywhere that it cancels out forward motion. Nowhere at all.

Apologies, skimmed posts too quickly and mixed a few people up.

Slightly boggling that some people think that because you pull up on one pedal, it cancels out the pushing down force on the other.

Somewher eon here it was said taht not even the fastest best cyclists pull up in anycase. Is that wrong?

RealMan

jonbonjovial wrote:

Somewher eon here it was said taht not even the fastest best cyclists pull up in anycase. Is that wrong?

Almost definitely I'd say.

bike-a-swan

Just found this on sheldon brown

'Standing pedaling allows you to apply more force to the pedals than is possible seated, because you can rest your entire weight on the driven pedal, and, even more, by pulling up on the handlebar, you can push the pedal with more than your actual weight...but is this a good thing?' (my emphasis)

Interesting, if nothing else

RealMan

Its true, and like we've said, you can put that handlebar bending force into the other pedal as an up stroke and get more drive, and less broken handle bars.

Oxygen Thief

I think the guy that said this hits the nail on the head...

There can be little doubt that if you apply a downward force on one pedal and an upward force on the other, then the total force is the sum of the two forces...

The argument here can only be:-

Due to the limits of the system, is it possible to apply these two forces in a way that one does not interfere with the other.

For example, by pulling up on one pedal affect the amount of force you can apply downards to the other?

If when pedalling along there is any time that it is possible to lift with the back leg without affecting the downward force on the front leg, then it is simple to see that the total power would be increased.

However, whether this is actually a useful effect is not clear.

warpcow

jonbonjovial wrote:
Somewher eon here it was said taht not even the fastest best cyclists pull up in anycase. Is that wrong?


Almost definitely I'd say.

I remember the same thing. A study showed that the best road riders simply unweight on the up stroke. Actually pulling used more energy than was necessary with little gain overall.

RealMan

How many times is a "study" going to prove something.

I would much rather trust experienced cyclists and cycling coaches.

supersonic

It was a study of experienced cyclists.

RealMan

Done by whom? What were they recording? Who paid for it? How many experienced cyclists?

warpcow

I would imagine that inductive science is what made all those physical laws. Only difference is Sir Francis Bacon et al weren't being funded by Shimano to 'prove' that SPDs are good

EDIT: I'm pretty sure it was linked to somewhere in the forum here, but it was at least a couple of months ago iirc

Oxygen Thief

RealMan wrote:

Done by whom? What were they recording? Who paid for it? How many experienced cyclists?

Same can be asked of who are these experienced cyclists and coaches that you are relying on?

supersonic

Exactly.

Most reports give the details if you look.

RealMan

Mostly guys that have been in it for decades, cat 2, 3, and 4 racers.

Yes, I'm sure the report would give details. But where is it?

supersonic

It depends on the report, but the one linked to earlier tested a group of pro racers and amateurs.

Anonymous

LOL, just read this from beginning to end, so funny.

I'm in the camp that being probably clipped in (with decent shoes) dose (for what ever reason) give you more power/increase peddling efficiency in certain circumstances.

Maybe not too much difference if your just peddling straight down a road, but in certain situations, sprinting for example. Especially up hill, I can see no reason why it's not going to give you a noticeable boost.

I've recently swapped my relaxed fitting Specialized Tamoa shoes for stiffer, tighter fitting Specialized BG Sport and one of the first things I noticed was I could get more power from pulling up with the back foot with my new shoes compared to the old.

Oh and SPDs and especially Eggbeaters make your bike look much better.

rudedog

This seems a very simple question to me - of course pulling up with your upstroke leg will increase the overall force.

The only way that pulling up wouldn't have an effect would be if you were already pushing down with the maximum possible force with your downstroke.