SPD's power advantage....Myth?

meanredspider

Northwind wrote:

mash up with my flats. On very steep stuff I run out of traction or pop the front wheel before I run out of leg power. Extra power when you're already wheelying or spinning isn't an advantage.

I think to some extent here you're confusing power and torque but it doesn't matter.

I don't believe everyone should use SPDs nor do I believe that SPDs are an advantage in every situation nor do you need to pull all the time in SPDs.

I actually think we're broadly agreeing.

wesk

Ok, so why do barends help you climb. Whenever it comes up on here, it's a normally stated as "rotates arm allowing larger bicep muscle to come into use" that's technically wrong, but the idea is there. Tha't be using the ARMS to brace your body to be able to put more torque through the pedals than weight alone would allow.

However, all parties have admitted, it's a benifit to be able to aply torque for longer (push / pull) than simple stamping will apply (excepting the fatct that a hyper mobile ankle can achieve this although that'd be difficult at a high cadence) therefore it is possible to have a higher average power via spd's for the average rider even if the top paragraph is (and it's about to be) shot down in flames.

Further, and this is the crux, anyone who rides falts is clerly a beginner and therefore unquailied to give a reasonable argument about why flats are better. Only spd riders have the experiance to know what benifits each type might have. :twisted:

And in addition to that, I did 30 miles yesterday, my legs ache but the bikes just been loadeed to the car so I'm off riding again

Northwind

meanredspider wrote:

I think to some extent here you're confusing power and torque but it doesn't matter..

They're a function of each other so as you say, it doesn't matter, they're not interchangable but they're inseperable.

meanredspider

Northwind wrote:

but they're inseperable.

They are inseparable but only at one point. The peak torque of a 150bhp motorbike engine is very very different from the peak torque of a 150bhp turbo diesel engine. Mashing your pedals to pull yourself up a steep slope has far more to do with torque than power. Flat out spinning downhill has far more to do with power than torque.

Northwind

Of course, but you can only pedal at one RPM at a time, and people's chosen RPM to attack a particular feature does tend to be pretty similiar whether on SPDs or flats- I know mine is. Still talking about short technical sprints rather than just simple straight line top speed of course, since that doesn't really apply much to most riders outside of racing IMO, we tend not to spin 100rpm up the hill. Recreational MTBers (other than single speed) operate in a fairly limited RPM range I reckon

But yeah, I should be making this stuff clearer, when I'm talking about effectiveness here I'm focusing only on a pretty limited range of conditions, because I feel that they're the ones that actually matter, and that's why I'm throwing out TDF comparisons etc entirely. The ability to put down a little more power doesn't matter much if you can only do it for 10 seconds and you could get up the feature on flats anyway, if you can sustain it then everything changes of course- to them it's like a turbo, to us it's nitrous And a very small can at that.

Or, to put it another way, 700bhp is worthless when you're cruising at 70mph. It's an advantage in some situations but not in others. So you take the suggested benefits and apply it to the real world situation you'll be using it in, and ask, does this actually, really help? Do I really use the potential? I know that now on flats I'm, oh, at absolute bleeding-edge peak a hair slower than I was on SPDs but that it never actually makes any practical difference. My overall fitness is decent but it's still the limiting factor over any distance, and on steep pitches it's traction and geometry and balance that's the limiting factor.

jason23

Northwind wrote:

jason23 wrote:

SPDs increase power and effieciency= FACT
This question has been answered by the pro's.
Do Tour riders use shoe/pedal connection systems?
Yes, End of debate.

The question that is left to be answered is "is this relevant"? Pros on the Tour use drop bars, should we? They all shave their legs, should we? Pros on the Tour also have no advantage to gain from flats so no counterbenefits, unlike us. They're also top end athletes, unlike us, and already have exceptionally honed fitness and technique, unlike us. A tiny efficiency saving is worthwhile at that level, it doesn't mean it's worthwhile at all levels.

Not end of debate.

Absolute rubbish

Northwind

Excellent counterargument So are we all top end athletes with shaved legs fighting for every second then?

meanredspider

Northwind wrote:

Of course, but you can only pedal at one RPM at a time.

Which means that the relationship between power and torque is pretty much meaningless.

You're right about individuals, though. Someone with a lot of muscle (a la weight-lifter) will be able to generate a lot of torque but may not be able to spin them fast enough to generate power (the human equivalent of a diesel engine). Somebody with smaller legs but is fit enough to spin them up fast, will generate lots of power but not much torque.

Northwind

meanredspider wrote:

Which means that the relationship between power and torque is pretty much meaningless.

Hmm, not sure what you mean by this? I'm not sure there's any time it's meaningless but it seems to me that this is where the relationship is clearest, once the variables get pinned down and narrow.

Anonymous

this thread will be put in the internet dictionary as a description of the word websters.

biff55

can we please get back to a FS V HT debate ?
there's more mileage in it.




Woo - Hoo !
i have now reached 1000 posts !
wots my prize ? VIP card ? key to executive toilet ? bike radar pen ?

meanredspider

Northwind wrote:

Hmm, not sure what you mean by this? I'm not sure there's any time it's meaningless but it seems to me that this is where the relationship is clearest, once the variables get pinned down and narrow.

Because both torque and rpm vary by rider & since power = torque x rpm x C (C = some constant). You can increase power by pedalling faster or harder or both (not to mention gears to optimise both). I thought we'd established that SPDs may increase the force (torque) you can apply and/or the speed at which you can pedal.

I think we're going WAY off course in this discussion....

supersonic

yeehaamcgee wrote:

supersonic wrote:

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?

If his feet were nailed to it, then still nothing happens. His feet would have to be nailed to the floor, not to the see-saw.

Indeed, but the rope tension would be higher.

supersonic

SPDs increase power and effieciency= FACT

Wrong. Read some of the reports I posted, the conclusions are anything but this.

Anonymous

supersonic wrote:

yeehaamcgee wrote:

supersonic wrote:

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?

If his feet were nailed to it, then still nothing happens. His feet would have to be nailed to the floor, not to the see-saw.

Indeed, but the rope tension would be higher.

But what does that mean though?
And how does it apply to riding, instead of the simple see-saw example?

NatoED

it does not increase force but smooths out the power flow .

supersonic

I am not too sure, as I haven't thought about it too much, but I beleive it could be significant in some extreme low rev cases. My brain is frazzled, long weekend lol, but will have a think and report if the grey matter comes up with anything.

Anonymous

supersonic wrote:

I am not too sure, as I haven't thought about it too much, but I beleive it could be significant in some extreme low rev cases. My brain is frazzled, long weekend lol, but will have a think and report if the grey matter comes up with anything.

Remember, in the see-saw example, the pulley is in a fixed point in space. On a bike, it's not, it's supported by your legs.
Not sure where to go from there, but I'd be interested to see what you make of it, since you have an understanding of mechanics too.

supersonic

Aye, will have a think! Was thinking on the lines of having the pulley o na beam attached to the seesaw fulcrum.

Torres

Just my tuppence... i'm not sure if it's been mentioned already, but surely techneaque has a big impact on power output and efficiency - and riding clipped keeps your foot around the optimal place to transfer power effectively.

I notice as i get tired my techneque begins to get worse, and my foot begins to slide further foreward on the pedals, so i'm no longer on the balls of my feet. Of course this isn't a concrete argument, and you could achieve the same power transfer on flats if you dial your techneaque, but clipless forces you to keep it perfect[ish].

pypdjl

supersonic wrote:

Wrong. Read some of the reports I posted, the conclusions are anything but this.

Are you sure? Those papers don't seem to mention flat pedals at all...

Northwind

Torres wrote:

Of course this isn't a concrete argument, and you could achieve the same power transfer on flats if you dial your techneaque, but clipless forces you to keep it perfect[ish].

Yup, exactly. Which to me is one of the 2 big advantages of clipless. Not going to be patronising and call it a skill compensator, it just gives you less things to think about. I have decent flat riding technique now at last but I'm pretty sure I wouldn't have if I hadn't spent time on SPDs, there's tricks that you can use on flats but are hard to learn on flats. Then again I've learned other techniques on flats that I never learned on SPDs.

So I guess what I'm saying is that for me, the best of both worlds is both worlds Controversial! I don't know if I'll be able to ride on SPDs again, but I think if I never had I'd be worse off. Relearning to ride on flats was a total bummer but also worth it.

Mental Mickey

Overtook quite a few people again today, all had Spd's bar me, a variety of bikes including some pretty lightweight looking expensive (Trek, Spesh etc..)one's here and there and all were in good physical shape by the look of them.

Yet strangley, I have my seat down for the climbs, as well as the downs, flats, my bike is a budget Alu HT (original cost would have been 800 quid) and I had a skinful of german beers last night and 2, yes 2 bags of pork scratchings.

What the hell is going on? 8)

Thewaylander

Scratchins are full of energy, and the beer sugars

So obviously you had fueled well, and by being manly your were allowed to destroy the lightweight orange juice drinking spd using..... (only joshing)

snotty badger

Maybe your just awesome?





:P

timpop

Both styles have there adantages but for me I use SPDs. I find I get more power transfer and better control for xc riding and endurance tests. I occasionally use the pull technique on some sections of trail as I can pull though it with a bit more power if needed. I don't think it's necessary to do it all the time, it uses more energy.

Can't wait for my evening ride tomorrow.

Shaggy_Dog

yeehaamcgee wrote:

When you're lying on your back, your weight is supported on your, well, back.
Both legs are in this case are independent.

When pedalling, your weight is supported on your feet.
If you could attach your trailing foot to the floor, or a moving contact point on the ground, you could use it as an anchor point to put more pressure through the leading foot.
Unfortunately, when it's attached to the trailing pedal, you can't because this pedal is directly connected to the other.
You cannot brace yourself against the thing you're moving.

The see-saw example a page or so ago should explain this.

You are right in this respect. The single largest force you can apply to the pedal is downwards with all your body weight. If you're stood up, pulling up with your trailing foot will only reduce the proportion of your body weight you can place on the leading foot, therefore providing no extra force, but no less either.

However, there is a flaw in your logic. You can't seem to let go of a static force diagram. Putting all of your weight down on the pedal at the horizontal position produces a maximum momentary torque, not power.

Mechanical power around a crank is average (not peak) torque x 2л x cadence / 60

Double the cadence, halve the torque and you have the same power output. Therefore you do not need to put all of your weight on the pedal to produce maximum power.

Power is generated from an average torque multilplied by your pedalling speed, by being clipped in, you are putting more power where you can't (as easily) on flats, at the dead spot, thereby increasing your average torque, thereby increasing your overall power. I agree you are not generating any more net torque from pulling up, what you are doing however is giving your quads a rest by sharing the burden.

So it really doesn't matter if you have a see saw supported by a spring with a guy pulling a string looped over a pulley attached to a separate entity, that's not a bike, it's not about force, or torque, it's about power

meanredspider

Well-argued, Shaggy-Dog. Well-explained.

I don't actually agree with

If you're stood up, pulling up with your trailing foot will only reduce the proportion of your body weight you can place on the leading foot, therefore providing no extra force, but no less either

as the crank is actually fixed, your foot is fixed to the crank and you are using your arms to add to the forces in the system. Sitting down adds another force and a pivot of sorts.

But, as you say, the torque applied is rarely the limiting factor. We rarely cycle (even using your simplified model) using our entire weight. You'd soon tire very quickly if you did (lifting your weight on one leg then the other) and power would be dictated by body weight.

The power point is one I tried to make several pages ago but you've explained it better.

Anonymous

I still disagree on this one. In the real world the only times I've run out of steam on a climb, are when I physically can't rotate the cranks any more and stall out. This is a typical scenario, where you reach your torque limit.
At those times I need to put my entire weight through the cranks, which is why I noticed no difference when riding SPDS or flats.
The pulling up aspect is nonsense. It does nothing when you need it. Sure, when you're seated, you can pull against the seat if you really want to , but it's still not doing anything of note.
Which is WHY, (again :roll: ) when they actually measured several professional riders' pedalling forces, they found that none of them pulled up on the rear, they just unweighted.

I DO agree that you can better propel the cranks through the deadspot with SPDs (I even said so several pages ago), but the whole pulling up thing is a myth. It is probably one of the most commonly believed myths in existence.

My contention is this myth. Pulling up achieves nothing of note, and when standing, when you NEED maximum torque, does nothing.

meesterbond

While I remember, here's a piece from Chris Carmichael's site on pedaling dynamics.

Even though Lance Armstrong’s pedal stroke received the greatest amount of attention during his post-cancer comeback, Chris and Lance had worked on optimizing his pedal stroke far earlier than that. Starting in 1993, Chris prescribed high-cadence intervals with the distinct instruction to focus on the kick over the top of the stroke and the pull through the bottom. Chris was careful not to ask Lance to “pedal in circles” because the force plate analysis had shown that no positive force was produced during the upstroke. Then, as now, the prevailing belief was that the best a cyclist could do was unweight the leg as it traveled through the upstroke. In other words, the best you can do with the upstroke leg is to get it out of the way so it doesn’t subtract from the force being exerted by the leg on the downstroke.