SPD's power advantage....Myth?
Comments
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bails87 wrote:sheepsteeth wrote:werent we discussing that tiny ball bag that sonic posted?
You mean that's not a normal sized one?!
mine gets that big after a hot shower0 -
yeehaamcgee wrote:Correct me if I'm wrong, but force in a rotational system would involve the amount of angular rotation per second, based on the amount of resistance. More force = higher RPM for a given load.
It all eventually boils down to the same thing really. The higher the resistance on the road, then the more force [and therefore torque] you need to generate to keep the same cadence.
The maximum power output is not at maximum torque though.0 -
but the maximum power you can put into the pedals would be the one that generated the most rotating force.
Spinning in a higher cadence just reduces the effective load.0 -
I am not sure I understand what you just said lol.
The maximum torque a cyclist can create will be where he creates the maximum force. But at higher revs the torque drops off and therefore force imparted - it is too fast for the cyclist to apply the force correctly as you are moving your legs very fast too which takes proportinally more of the energy.
Maximum power usually occurs at a lower torque. Eventually the cyclist is spinning so fast that the gear will be very very low to achieve it or has spun out - virtually no resistance, virtually no torque.0 -
By changing the gearing so you can use a higher cadence, you are reducing the amount of power required to move the bike, correct?supersonic wrote:I am not sure I understand what you just said lol.0 -
If the velocity of the bike stays the same, then the work done per unit time is the same. You will will be operating at lower torque, but proportinally higher cadence.0
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Hmm, you're right.
Ok, so do we (I?) now agree that by putting your entire bodyweight through the cranks and using a lower cadence increases torque?0 -
For most cyclists I would say it produces the maximum peak torque during the 360 degree rev of the crank. That first graph I linked to shows that this is possible up to quite a high cadence before it trails off.
Infact most studies show that for the average cyclist peak torque is indeed on the pushing downstroke, and actively trying to pull reduces peak positive torque.0 -
Right, I think I used the term "power" interchangeably with "GRRRR, HULK" kind of power
that graph you posted doesn't seem based on any concrete figures though, simply assumptions. I would be incredibly surprised if anyone could maintain that much relative torque up to 150RPM.0 -
I think I see where you were getting confused Yeehaa. Torque is a force. It is possible for this to be maximised at a certain point in time. Assuming no pulling up is happening, this will be when the entire body weight is on the front pedal, and when the pedal is horizontal. Power, on the other hand, is a force multiplied by the time it is applied for. So for maximal power, you can have a lower peak torque if the average torque is higher.
Let's assume no pulling up is possible with the back foot. On flats, you have a downward push, and a dead point, where no torque is generated, at the top and bottom of the stroke. When clipped in, you can push the pedals through this dead point. The peak torque generated on the downstroke is identical to that on flats, but as there isn't the zero torque moment at the dead spot, the average torque is higher, and therefore the possible maximum power is higher (I know it's technically possible to drive through the dead spot on flats, due to hypermobile ankles and very grippy shoes I can do one footed pedalling on them, it's just not easy for most people). This power is what drives the bike forward, therefore you can go faster (even if it's only a tiny fraction) while clipped in.
Now, onto the point of pulling up. It is possible. I've done it, many times. I can tell, because my road bike shoes are a little loose fitting, and my back foot lifts up off the bottom of the shoe at low cadences, even when out of the saddle. You posted an argument a few pages back that this should be impossible, giving the example of trying to lift up a set of bathroom scales while standing on them. This is a poor example, because you're not just working against your body weight. In addition to this, you're working against the resistance from the road, transmitted through your chain. I don't know how much of an advantage this gives, if any advantage is given at all this, as I don't have access to a power meter to do the experiment, but pulling up on the rear pedal IS possible.0 -
A, I get you.
But, I still contest that pulling up achieves nothing. I wholeheartedly agree that you can push over the very top and bottom of the stroke better with SPDs, and stated this very early on.
If you're pulling the rear pedal, you're not pulling against anything, you're just pulling yourself downwards. If you're seated, you can pull the pedal by being braced against the saddle - but this means you're not putting as much pressure onto the front pedal, which negates this.
I rally can't be arsed stating this over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over0 -
Why do your legs ache after riding for a long time?yeehaamcgee wrote:If you're pulling the rear pedal, you're not pulling against anything, you're just pulling yourself downwards. If you're seated, you can pull the pedal by being braced against the saddle - but this means you're not putting as much pressure onto the front pedal, which negates this.
I rally can't be arsed stating this over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over and over
If maximal power is just putting your body weight on the pedals, then they wouldn't. You'd still get some exercise from the movement, but you'd get little muscular ache, as you wouldn't really be using your muscles. This isn't what actually happens, though. In reality, you use your bodyweight and the force of your muscles together to overcome the resistance of the rear wheel on the ground, air resistance, etc.
Unfortunately, this is really hard to demonstrate. It's possible to get one pedal pushed down purely by body weight, but very difficult to actually ride just using body weight. Just think about it for a while, properly. You should be able to see that putting power through the drivetrain of a bike cannot simply be due to body weight, there has to be some extra work. If this extra work is present, it can come either from pushing down on the front pedal, or pulling up on the back pedal. To the bike, it's exactly the same.0 -
whyamihere wrote:If maximal power is just putting your body weight on the pedals, then they wouldn't.
I don't think he's saying that all you're doing is putting your weight on the pedals- rather that when you pedal, your leg is pushing against your body weight. Not the same thing.Uncompromising extremist0 -
Same effect though. Your weight is a force, with a magnitude of your mass multiplied by the force of gravity. If you're pedalling purely by pushing against this force, the maximum force you can put into the pedals is your weight, otherwise you'll push yourself up off the pedal.0
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Same reason they would if you'd been doing squats for a long time, basically.whyamihere wrote:Why do your legs ache after riding for a long time?
Right, here's something that helps clarify my view on this.
Imagine you're standing on one end of a giant see-saw, there is a resistance (call it a spring) under your end of the see-saw, that exactly counteracts your weight.
There is a pulley suspended in the sky (a 1:1 pulley).
You have a rope attached to the opposite end of the see-saw, that goes through the pulley.
If you pull on the rope, will the see-saw turn clockwise?
Nope.
Does that make sense?0 -
Can the tension in the rope be more than your body weight though?0
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I'd be intrigued to know how.0
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nickfrog wrote:Great post actually. I am amazed how aggressive the "anti-SPD" brigade is on a subject that is such a personal choice. SPDs are not compulsory. If you don't want them, don't buy them, don't use them. Live and let live.
Yet it has to be said that it is in fact the 'pro spd brigade' that often belittle users of flat pedals by making comments such as 'you can tell the beginners as they haven't yet progressed to spd's'.
How utterly arrogant, pot kettle and black spring to mind. 8)0 -
^ Thats how I see it too.
"The pros use clipless so the flat users must be beginners"0 -
Just to throw my 2p in to the discussion...
I think what you are forgetting is that riding a bike isn't just about using your legs to push on the pedals. Riding a bike requires your whole body - your legs, core and arms too. If riding with al lot of "power" was simply about putting the most weight on the downward pedal, surely there would be a lot of very fat competitive cyclists doing much better than the lightweights. By using the top of your legs to grip the saddle, and your core and arms to pull you down on to the bike, you can put much more force through your pedals. This is true whether you just push or push and pull.
To try and use a clear example, if you watch a track rider in the team sprint accelerate from the gate you can easily see that they use their whole body to get the bike moving as fast as possible as soon as possible, pushing and pulling hard with their legs, and using their arms and core to help get than power through the pedals, rather than popping them off the top of the bike. Now imagine them trying to do a sprint start without holding on to the bars. Only gravity would be holding them on their bike and their legs would easily make them stand up or fall off. So in this example, being firmly attached to your pedals certainly does let put more power through the pedals because the total force you can apply depends on your leg strength and the strength of the rest of your body.
Going back to the bathroom scales thing will let you easily demonstrate this. Stand on the scales and you see your weight. Still standing on the scales, bend down and grasp the base of the scales with your fingers. Holding tight, push down with your legs and your apparent weight will go up because you can push harder on the top of the scales. You're no longer just pushing against gravity, but gravity + your grip.
And remember the OP - it was about advantages to SPDs. Yes, there are advantages, but like most things in life, there are disadvantages too.
I don't give a hoot what people ride. I come from a road background where riding with flats has no advantages, so I ride SPDs on my XC bike too because that is the technique I'm really good with. Yes, I ride XC, so I'm one of the lycra clad brigade who likes getting places quickly.0 -
bmbgrs wrote:
I think what you are forgetting is that riding a bike isn't just about using your legs to push on the pedals. Riding a bike requires your whole body - your legs, core and arms too..
Spot on. After a hard fast ride (trying to keep up with my colleague who is a greased weasle on a bike) it's my lower back that hurts not my legs. I've also been astonished about how my upper body muscles have developed through cycling.
Besides all that, my own experience (I was trying it this morning again) shows I can generate more power pulling and pushing (and I'm not particularly good at it as I usually focus on pushing). I don't doubt it's less "efficient" but rarely is more power more efficient.
Gravity is interesting in the debate but a bit of a red herring - else recumbant (sp?) bikes wouldn't work - and I'm sure they do...ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH0 -
Yes, gravity is a complete red herring! People that ride 'bents are doing all their pushing against the back of their seat, so should be able to get a massive amount of power down, probably only limited by their legs/pain threshold/seat strength!
Efficiency is a very difficult topic as it varies so much from person to person, but generally pedaling a higher cadence at a lower force is more efficient for most people.0 -
just to add more food for thought....
interesting blog post here:
http://www.bikejames.com/
from James Wilson. He's the guy that is coaching Aaron Gwin in some of his bike fitness aspects, so not just any old bloke with an opinion....Whenever I see an adult on a bicycle, I believe in the future of the human race.
H.G. Wells.0 -
yeehaamcgee wrote:A, I get you.
But, I still contest that pulling up achieves nothing. I wholeheartedly agree that you can push over the very top and bottom of the stroke better with SPDs, and stated this very early on.
So what's your argument? If you agree that you can generate power clipped in at the dead spot and you don't generate any less than on flats at the mid stroke then the only logical conclusion is that you can generate more power being clipped in. End of story... Nearly
However there is something I think you're not fully comprehending yet.
Stop thinking about putting your full weight on the leading pedal and consider that you can produce more power sat down spinning. OK, so you're not putting all your force through the pedal, but you're doing it again and again and again in rapid succession, this is where the power comes from. Using full torque on the pedal is not an efficient way of pedalling since it can't be repeated as quickly. This is where the advantage of being clipped in comes in because you are sat down and can pull up slightly, it is only slight, but it's there, plus you can pedal in circles rather than just pushing down.
So, that's it explained in a road sense, off road there are other advantages. Because the various types of terrain pose traction issues, it is way more efficient to keep your bum in the saddle when climbing. Roadies tend to get out of the saddle on climbs to generate that extra bit of power (still spinning a high cadence), unless you're on a very smooth grippy surface or if the climb is VERY steep, that's not generally a good idea off road, this is why MTB's have much lower gearing than road bikes.
Plus, some people like being attached to the bike, but we're not talking about that because that is personal preference. These are just the facts.
I'm not trying to force people to go clipped in, but there is clearly more power to be produced by doing so. If the question "can you get more power from SPD's?" is asked, the answer is yes, providing you pedal properly in the first place.I had to beat them to death with their own shoes...
HiFi Pro Carbon '09
LTS DH '96
The Mighty Dyna-Sore - The 90's?0 -
CycloRos wrote:Blimey this thread is still going!
I agree, top post Shaggy_dog!
There is definitely a an anti-XC mindset expressed by a lot of riders in the UK, usually by the non-competitive so called trail riders.
I don't see a difference between XC and trail they both involve the same kind of terrain (generally). I have the utmost respect for anyone that races but no more than your average joe out on the trail.
Ride what you like, how you like and don't bow to the supposed 'cool' crowd!
I consider XC anything that gets you from point A to point B off road, on a bike, not wholly assisted by gravity. Hence why it is called cross-country, because you go across countryside. Ergo, "trail" is XC, "all-mountain" is XC. A Specialized Enduro is an XC bike, my Gary Fisher HiFi is an XC bike. So when I say XC I actually mean "going out for a ride"I had to beat them to death with their own shoes...
HiFi Pro Carbon '09
LTS DH '96
The Mighty Dyna-Sore - The 90's?0 -
yeehaamcgee wrote:Right, I think I used the term "power" interchangeably with "GRRRR, HULK" kind of power Laughing
it's probably worth emphasising that power doesn't actually exist. It's just a calculation! Torque on the other hand is a quantifiable measurement.
That is the end of the story as far as the science theory goes! Whether it works in practise for us mountain bikers is blatantly down to personal preference.you can generate power clipped in at the dead spot and you don't generate any less than on flats at the mid stroke then the only logical conclusion is that you can generate more power being clipped in. End of story...0 -
CycloRos wrote:yeehaamcgee wrote:Right, I think I used the term "power" interchangeably with "GRRRR, HULK" kind of power Laughing
it's probably worth emphasising that power doesn't actually exist. It's just a calculation! Torque on the other hand is a quantifiable measurement.
That is the end of the story as far as the science theory goes! Whether it works in practise for us mountain bikers is blatantly down to personal preference.you can generate power clipped in at the dead spot and you don't generate any less than on flats at the mid stroke then the only logical conclusion is that you can generate more power being clipped in. End of story...
Torque is a function of force and radius of rotaion actually. Power is force over time. ther discussing different focuses now.
In terms of torque and the maximum applied it will aways be maxed at the horizontal line(verticle force application) in a cycling system. and will not be different from spd to flat. The difference is at the verticle where with spd's you can apply a small amount of horizontal force rather verticle. there for you average power output if cycling perfect can be increased not the torque. but the actual figures are fairly small for the effect of fwd power and the verticle axis.
Ok?0 -
yeehaamcgee wrote:I'd be intrigued to know how.
I was thinking (lets say the ropes are purely vertical to remove any horizontal forces) the maximum rope tension would equal his body weight ie he would lift himself off the see saw. But what if he nailed his feet to the seesaw?0 -
Ok, two questions...
Why, with a decent set of flats and shoes, can you not apply any force at this 'dead spot'?
Secondly, it seems to have been assumed that 'pulling up' on the up stroke is even possible when from memory there have been studies which concluded that the best that can realistically be achieve is an 'unweighting' of the back foot. Again something that can be done just as easiely with flats.0 -
Well you can apply force at this point on flats.
Thats part of the point, its a bit easier on spd's but on flats its more about technique, mostly you can just forget on spd's.0
