First attempt with SPD's today in 30 mins

supersonic

No, because of the way the object is supported. The suitcase scenario is different.

bails87

supersonic wrote:

To be able to pull up on the pedal, you must push down somewhere. That is... the other pedal.This is most true for sprinting out of the saddle, when we accelerate maximally.

The forces do not add together.

But pushing down on the leading pedal is what you want to do, that is was drives you forwards :?

It's all too confusing

supersonic

Get a bike with SPDs. Put it in a big gear. Jump on it, put all your weight on one pedal. Stop. Put all your weight on one pedal, whilst pulling up on the other pedal. You will accelerate much, much quicker

So where is the balancing force coming from for this pull up?

Pushing down on the opposite pedal.

It balances out.

RealMan

supersonic wrote:

Get a bike with SPDs. Put it in a big gear. Jump on it, put all your weight on one pedal. Stop. Put all your weight on one pedal, whilst pulling up on the other pedal. You will accelerate much, much quicker

So where is the balancing force coming from for this pull up?

Pushing down on the opposite pedal.

It balances out.

Exactly! You're almost there.

So you apply your weight to down stroke on one pedal.

You then apply your muscles force on the up stroke to the other pedal.

This causes the force on the down stroke pedal to increase.

Thus both pedals have increased force.

cgarossi

RealMan wrote:

I'm sorry but they do.

Again, another experiment I suggested a few pages ago.


Get a bike with SPDs. Put it in a big gear. Jump on it, put all your weight on one pedal. Stop. Put all your weight on one pedal, whilst pulling up on the other pedal. You will accelerate much, much quicker.

cgarossi wrote:

They aren't

One is being pushed, the other pulled. Two wholly different actions, and the two cranks are one and the same! If they were seperate it would be a different matter.

Your downwards push is translated into an upwards push on the other side, cancelling out your efforts to pull it up. And vice versa. If you could apply extra power to the upwards pull it would cancel out any efforts made towards pushing on the opposite side crank.

It only becomes effecient when there are both pushing and pulling in equal amounts since you end up using effectively half the muscle power in each leg but getting the same amount of power. But in reality that never happens.

I would love for you to meet my physics professor, he would cry if he heard you talk like that. The forces combine. Again, think about a weaker man and a stronger man pushing a car.

Why do you think tug of war teams exist? Surely, if they're not all pulling at the exact same force, there's no point having all the weaker guys?

You're wrong. Im sorry but you just are.

The car scenario doesnt work with this.

The tug of war scenario doesnt work either since they are both pulling.

I suggest you go and talk to your physics professor.

RealMan

Do you have kids that go to school? Do you work in a school yourself? You could go talk to any physics teacher and they would be able to explain this to you.


There is no difference between pulling and pushing.

rubins4

No bails, I believe you are right with the suitcase analogy. The forces would be working in the same direction as eachother, so would be combined.

I agree with SS regarding standing up. You can only use the force your bodies mass produces due to gravity (ie -your weight), as anything used in the upstroke will be taken away from the down stroke.

Infact, I agree with SS as regard to sitting down too. You may be able to achieve a slightly greater force with the upstroke as you are acting against the seat with your muscles, but how effective this would be I dont know.

Seems like a bit of a bone thread tho. Unless someone has some conclusive proof, its all just hot air an opinion.

bails87

supersonic

This causes the force on the down stroke pedal to increase.

Thus both pedals have increased force

Totally wrong. You cannot produce more force than your weight. It does not cause it to increase. As you are supporting yourself on the pedals.

cgarossi

:roll:

Ever seen a train with two engines? One at each end?

Why do you think that is? To conserve fuel. Not go faster.

Pushing and pulling is more effecient when dividing the power reserves available.

They may be a 1000BHP each, but they will never, ever, reach a speed equivilent to a 2000bhp train.

RealMan

Ok. For about the billionth time.


Scales represents your down stroke pedal.

Shelf or table represents your up stroke pedal.

RealMan wrote:

Go put one foot on a set of scales. Put the other foot under a table or low shelf, and push it up with your foot. Suddenly the scales reading increases, plus you have the force on the shelf/table.

cgarossi wrote:

Ever seen a train with two engines? One at each end?

Why do you think that is? To conserve fuel. Not go faster.

Pushing and pulling is more effecient when dividing the power reserves available.

They may be a 1000BHP each, but they will never, ever, reach a speed equivilent to a 2000bhp train.

But by your earlier logic, unless they are both outputting the exact same force, the weaker one makes no difference at all.

What's the probability of two engines producing the exact same force? Yes, that's right, 0.

rubins4

RealMan wrote:

Ok. For about the billionth time.


Scales represents your down stroke pedal.

Shelf or table represents your up stroke pedal.

RealMan wrote:

Go put one foot on a set of scales. Put the other foot under a table or low shelf, and push it up with your foot. Suddenly the scales reading increases, plus you have the force on the shelf/table.

In that senario you are using the shelf which is fixed. On the bicycle you are using a position to balance against which is not - the other pedal. Because the pedal is attached to the other one via the cranks/BB, wont any extra force put into one be negated by the other? You are using you muscles to exert a force against the shelf, but on the bike you are exerting a force against yourself, so would be cancelled out?

cgarossi

I appologise, my train analogy is wrong.

The reason is this:

When you push down on the crank, the opposite crank moves the same distance and moves away from the source of power, your pulling foot. You can never apply more force, since pulling it will remove it from the pushing.

supersonic

Stop the attitude. I have told you once.

When you 'pull up' you shift your weight to the opposite pedal. Hence you are really pushing down. That is the crux of the matter as you are supporting yourself on the pedals. There is no net increase in force when out of the saddle, unless you can brace yourself elsewhere AND NOT AGAINST THE OPPOSITE PEDAL.

supersonic

rubins4 wrote:

RealMan wrote:

Ok. For about the billionth time.


Scales represents your down stroke pedal.

Shelf or table represents your up stroke pedal.

RealMan wrote:

Go put one foot on a set of scales. Put the other foot under a table or low shelf, and push it up with your foot. Suddenly the scales reading increases, plus you have the force on the shelf/table.

In that senario you are using the shelf which is fixed. On the bicycle you are using a position to balance against which is not - the other pedal. Because the pedal is attached to the other one via the cranks/BB, wont any extra force put into one be negated by the other? You are using you muscles to exert a force against the shelf, but on the bike you are exerting a force against yourself, so would be cancelled out?

Excellently put.

stuart_c-2

supersonic wrote:

Totally wrong. You cannot produce more force than your weight. It does not cause it to increase. As you are supporting yourself on the pedals.

What if you're using your upper body to brace yourself? Think how much more pressure you put through your handlebars when really honking it out the saddle. Is this not you trying to brace your body against the force of your leg pushing down?

Just a thought.

weeksy59

SO, should i get the other bloke to send me back my pedals

Oxygen Thief

When you push down on the crank, the opposite crank moves the same distance and moves away from the source of power, your pulling foot. You can never apply more force, since pulling it will remove it from the pushing.

That should sum it up for everyone. No extra force can be generated simple. Efficiency is the only arguement in these things in my eyes. People that say they can get up a hile quicker in them then yes they can because they recruit more msucles to do so so there's less load on each muscle letting it work harder for longer.

cgarossi

Yes. Every action has an equal and opposite reaction.

stuart_c-2

Ah, my post above kinda goes with what SS put a couple above me. Don't know how efficient it is, but trying to use your arms and upper body through the bars is 1 way trying trying to "brace" yourself and exert more force?

supersonic

In a hard sprint the cyclist actually pulls up on the bars.

But in theory it should be achievable, and possibly is to a lesser extent with a lot of riding.

RealMan

supersonic wrote:

Stop the attitude. I have told you once.

When you 'pull up' you shift your weight to the opposite pedal. Hence you are really pushing down. That is the crux of the matter as you are supporting yourself on the pedals. There is no net increase in force when out of the saddle, unless you can brace yourself elsewhere AND NOT AGAINST THE OPPOSITE PEDAL.

Sorry, I'm a bit ill.

Stuart_C has a good point, the same point I made earlier somewhere. Better to put handlebar bending force into the pedals then the handlebars.

The fact the the table or shelf is stationary is moot, it makes no physical difference.

rubins4

Stuart- I would say that is the same for flats or spds. You wouldnt be able to pull up on the bars to aid the upstroke with spds and achieve more force tho.

(I appreciate thats not quite what you are saying, and i think you are right, but this thread is getting a bit complicated to be having side discussions going on! )

Oxygen Thief

Stuart_C wrote:

supersonic wrote:

Totally wrong. You cannot produce more force than your weight. It does not cause it to increase. As you are supporting yourself on the pedals.

What if you're using your upper body to brace yourself? Think how much more pressure you put through your handlebars when really honking it out the saddle. Is this not you trying to brace your body against the force of your leg pushing down?

Just a thought.

You can produce more force than your weight of course you can. Just need the same force going in the other direction, ie onto your handlebars.

cgarossi

Yes. But you can only apply force in one direction when two opposite forces are applied to the same resistive force.

rubins4

RealMan wrote:

The fact the the table or shelf is stationary is moot, it makes no physical difference.

The fact it is stationary is moot, but the fact it is a fixed object that you are exerting a force on isnt. On the bike, the object you are exerting your force on is not fixed, but is working not in opposition as such, but 'counter' to the direction of your initial force. So, I believe that by adding to the upstroke you are taking away from the downstroke, so no additional force can be applied.

bails87

Well, I'm going to keep using whichever pedals I want, if that's ok with everyone?

RealMan

Ok think about a brick wall.

One person stands on one side, and pushes against it with a small force.

Another person stands on the other side, and pulls it towards him with a slightly different force.

The total force is both the pushing and the pulling forces combined together.

rubins4 wrote:

So, I believe that by adding to the upstroke you are taking away from the downstroke, so no additional force can be applied.

No, it does actually increase the down stroke, otherwise you would fly, because the upwards forces would be bigger then the downwards forces.

cgarossi

You're forgetting there is a resistive force in the Pulling too if the power is not the same.

So, TotalPower = Pushing - Resistance(+Pulling)

This does not apply to cranks though. Cranks are not walls.

supersonic

RealMan wrote:

Ok think about a brick wall.

One person stands on one side, and pushes against it with a small force.

Another person stands on the other side, and pulls it towards him with a slightly different force.

The total force is both the pushing and the pulling forces combined together.

That is true. But think about this:

Stand on a weighing scale. Now pull up hard against an object nearby, eg the sink. The force increases right? Yep. This is what you are saying for the bike. Seated this may be the case.

But place a bar on the weighing scales, and stand on it. Now pull up on it. Nowt happens. No matter how hard you pull, your feet will create an exact opposite force and balance it out. This is my anology for the bike, and how the mass is supported [again I will say for the sprinting out of the saddle case]