WhyFi

Nice edit.

No, we actually do have to provide all of it. How long do you think that your experienced, supple, springy legs will continue in pedaling motion without input from you or the drivetrain? It's probably generous to give it two revolutions before grinding to a halt.

kbarch

Not long, and two revolutions is certainly longer than you have previously suggested, so maybe that is generous. However, my legs never grind - to a halt, or otherwise. Maybe that's the difference.

Meanwhile, let's go back to high school physics for a moment. Let's consider Newton's Cradle, and compare the ball we lift on one side with our legs, and the ball that goes flying out and back as the wheel. If the ball we lift is made of Plasticine, instead of steel, like the usual ones, it wouldn't work very well, in fact, it would hardly work at all. You and others seem to have been asserting that our legs are much like Plasticine, and they are only mechanically effective when we expend energy to stiffen them up and force them to be. I'm not suggesting our legs are as elastic as steel, and I'm sure you're right about how a nominal level of force we may apply often just seems like none rather than actually being none, but I'm also sure our legs are more and better than some kind of clay that manages to harden through force of will and immediately soften when released. How much better they are is unknown, and therefore it is also unknown how advantageous that difference is, so I think it makes sense to simply agree to disagree here.

tomato coupe

And therein lies the problem. You don't seem to be able to grasp this basic concept. Several people, with better understanding of physics, have tried to explain this to you, yet you refuse to accept it. You can remain ignorant of physics or you can try to learn something from others. Your choice.

Trakhak

On a fixed-gear bike, the rider is either expending pedaling effort or not.

On a fixed-gear bike, if the rider is not expending pedaling effort, the rider is slowing the bike.

("Pedaling effort" includes pedaling at an effort level that is just high enough to keep from slowing the bike.)

At the risk of triggering yet more logorrhea from those who deny the validity of those statements (and are apparently willing to continue to deny them into the distant future), here's another:

The statements above hold just as true for freewheel-equipped bikes as for fixed-wheel bikes. The only difference is that a pedaling effort that is too low to propel the freewheel-equipped bike will not slow the bike.

Edit:

Riding a fixed-gear bike downhill can create the illusion that the legs are being kept in effortless motion by some form of circular momentum. After all, you're putting no effort into pedaling, and yet the bike isn't slowing or may be accelerating!

That particular illusion is a consequence of the use of clip-in pedals or toe-clip pedals for foot retention. Try riding a fixed-gear bike without foot retention on a steep downgrade at, say, 180 rpm or so; it'll be immediately obvious that you're expending a lot of effort to keep your feet in circular motion.

By the way, here's my pro tip for high-speed descents on a fixed-gear bike: forget about pedaling in circles. Instead, think of the pedaling circle as becoming flatter and flatter as your cadence goes up. At over 200 rpm, I'm kicking forward, aiming at the point corresponding to 4 o'clock in the pedaling circle and letting the pedal drag my foot back, up, and over.

kbarch

It's not a basic concept of physics that our legs are actually inelastic, or have any other such properties for that matter, it's just that people with a grasp of high school physics can ignore their material properties and internal mechanisms in order to simplify the description and make calculations without getting into differential equations - calculations where, as it happens most of the time, the effect of the legs' properties would not make a difference. When we're talking about working to pedal any bike, skid-stopping a fixie, or coasting with a free hub, sure, in terms of simple physics, it doesn't matter what they're made of or how they work.

However, when we start talking about what happens when we are not attempting to move or stop a fixed gear bike or when we soft-pedal a free hub bike, there is every reason to believe it would make a difference what our legs are made of and how they work internally. You can refuse to accept the complex realities of anatomy and insist upon simplification if you want, but that doesn't make your explanation sufficient, even in terms of physics, in all cases.

@Trakhak is correct in asserting that in order for the rider of a fixed gear bike to prevent it from slowing down, some "pedaling effort" has to come from his side of the drivetrain, because the rolling bike is not friction-less (and sure, neither are his legs). However, there is no evidence to support the notion that what's coming from his side of the drivetrain cannot or does not involve the release of elastic potential energy. Of course, even if we had a great deal of it to release after our knees bend each time around, it would never be sufficient to entirely prevent the bike from slowing down, so something more is required. But whatever little we do obtain in the way of elastic potential energy may well be enough to allow us to observe the reduction of some losses, losses which could not be eliminated when coasting on a free hub. Even if it's just a matter of allowing the legs to bounce up and down a time or two, as it were, that's no extra effort from us, whereas stiffening them up to stop them and coast on a freehub requires some - just not very much, or on a continuous basis - unless we're the type to take the opportunity to flex our legs isometrically while we're at it, which I think many of us do instinctively.

Over an extended period (more than a couple of seconds), I imagine the advantage of coasting vs relaxing on fixed would be a factor of the cadence at which one started. Starting from a high cadence, coasting is clearly advantageous; it takes work just to maintain control, and one may slow down significantly right away. At lower cadence, however, I think there's reason to believe that relaxing on fixed is advantageous, due to the natural "cruise control" effect described previously. Any little extra effort along the way may add up to less than the extra effort required to eventually get going again after coasting - the coaster would experience more of a loss at the end. I imagine it would be somewhere around ones average cruising cadence that the advantage between coasting and "flywheeling" would tip.

By the way, Trakhak, about your edit add .... The first part is consistent with what I was just saying about cadence. But the part I really like is the last paragraph. Even though I've never spun anywhere near 200 rpm - over 160 yes, maybe pushed 180, and not on a descent, but I totally get where you're going with the pedaling circle becoming flatter thing; it's a fascinating adaptation.

StanSeven

Good discussion until recently. If you want this thread to continue, no more personal insults please.

Thanks

Stan

Edit: posts deleted to clean up thread

Brian Ratliff

For all the arguing, as much as I can follow, pretty much everyone is somewhat wrong in this thread.

Freewheel drivetrains are somewhat less efficient than fixed gears for a couple reasons:

1. Freewheels have almost no momentum in the drivetrain to aid the pedals to go around. The only flywheel in the system is the chain and the crankset. No, the legs don't count; they don't have an angular momentum component -- they are reciprocating meaning they change direction, meaning their momentum through a cycle cancels to zero. When you stop pedaling, your legs stop almost instantaneously as the wheels disconnect from the drivetrain, no matter how fast the bicycle is going or the rider is pedaling.

Fixed gears, on the other hand, have the momentum of the crankset, wheels and the entire forward motion of the bicycle and rider as momentum to aid the pedaling action. You can pedal to much higher RPM on a fixed gear because of this, and sprinters and power climbers can accelerate faster because the momentum of the bike is used to even out the pedal stroke. The drivetrain is always in motion with a fixed gear and does not need to be re-accelerated with each power stroke. This is basically the effect of putting a flywheel on a gas engine. And it's quite a bit of momentum: enough that if you are going 20 mph on a fixed gear on level ground and simply stopped pedaling, you can be made to catapult over the front of the bike. Track racers have the concept of "float", which means your legs are going around the pedals with minimal effort, aided by the momentum of the bicycle. Your legs are still moving, aided by the momentum of the system, but not driving your bike forward and you can reengage with the pedals almost instantaneously. When you float to bleed speed, your legs are actually being driven around by your drivetrain, so you are exerting zero energy, even though your legs are still moving.

2. Freewheels which feature shifting gears have less efficient engagement with the chain than fixed gear drivetrains. The teeth on a fixed gear cog and chainring is a true involute shape and features only rolling contact with the chain roller. A shifting freewheel allows partial sliding engagement so the tooth profile can be optimized for shifting. Cogs and chains on fixed gears don't wear anywhere near the rate of freewheel chains and cogs.

Now, obviously, comparing a fixed gear with a freewheel usually means the freewheel has multiple gears and so on system efficiency, the freewheel is going to win since the fixed gear rider is going to be in their optimal cadence only a small fraction of the time.

Carbonfiberboy 

^Too bad you didn't embolden drivetrains because as should be obvious, nothing else about a fixed gear bike is as efficient as even a SS bike. Were that not the case, it would not be so easy for a SS bike to drop fixed riders.

FBinNY 

I'm sorry to bring the bad news, but if everyone else is only somewhat wrong, they have you beat.

This is wrong, and there's no evidence that supports it. If bikes work as you posit, we'd hear the noise of disengage and re-engage from the freewheel. If fact we do sometimes run into this with newb riders, but it takes only a very short time for riders to achieve 100% positive full time driving engagement. So the rear wheel is NEVER driving the crank in normal forward pedaling conditions. Yes the power varies from the peak to near zero, but the rider, and not the wheel is always turning the cranks. OTOH - if the wheel were turning the crank, that would imply reverse (slowing) torque applied to the wheel in accordance with Newton's Laws, and we'd see a slight loss of speed with every cycle.

Sorry again, but no.

All of the pointy part tooth above where freewheel sprockets are cut off, has no effect on power transmission in any way. This is for the very simple reason that it never (under normal conditions) touches anything. In fact it can't. Each link of the chain swings into position pivoting around the engaged link preceding it. It never comes any place close to the points (try on your own bike observing carefully).

The ONLY reason chain sprockets are cut with pointy teeth that way is to improve the margin of forgiveness as the chain wears (stretches) and more gently pick up the teeth. One look at a worn sprocket or chainring will confirm this, as you'll see wear on the driving side of the trough and the "strike" zone immediately above, but zero evidence of any contact beyond that.

Now, obviously, comparing a fixed gear with a freewheel usually means the freewheel has multiple gears and so on system efficiency, the freewheel is going to win since the fixed gear rider is going to be in their optimal cadence only a small fraction of the time.[/QUOTE]

Carbonfiberboy 

^FB, I think Brian is correct. I don't think that a SS bike would beat a FG track racing. If there's a case of that which I don't know about, please enlighten us all. Anyone who's ever done OLP on a SS and a FG knows that the SS is much harder to operate one legged. Thus the same thing applies to both legs. It's just easier if the drivetrain brings the pedal over the top for you instead of having all those complicated bits of muscle having to do it. May the biggest legged rider win. But that a very special case for most people in the world because it only applies on dead flat terrain. Outdoors, SS bikes are faster than FG and geared bikes faster than SS.

If I'm not mistaken, the silly guys in Le Ride were on modified bikes with alu rims, different BBs, freewheels, extra chainrings and cogs, and multiple chains carried in their support vans.

FBinNY 

This is very simple and straight forward, and this will be my last post on the thread.

The ONLY way fixed vs. freewheel (overrunning clutch) can make a difference, is if the rear wheel overruns the cranks at some point in the cycle. Otherwise the freewheel, functions as a solid block of metal, the same as a fixed sprocket. However, overrunning never happens when applying power, and it's your legs' muscles that carry them past the dead spots.

If overrunning did happen, you'd hear it with a freewheel. If it happened on a fixed wheel, Newton's laws dictate that any force applied to keep the legs moving would imply an equal ******ing force applied to the wheel, so advantage to the freewheel (if the rear wheel overruns the crank --- which it doesn't during normal pedaling).

In short, IF the rear wheel were used to carry the crank through the 6/12 crank position, it would slow the bike in the process, because Newton's Laws demand it. If you argue against that by saying it doesn't slow the bike because there's no force involved (forward and/or back) we're back to square one where fixed/free doesn't make any difference.

Feel free to disagree and post. I'm happy to let any who care block this out in their own mind, following either my or anyone else's logic, and decide for themselves. But I stand by my claim, that fixed or free ONLY makes a difference in descents where fixed introduces "engine braking" that freewheel doesn't.

79pmooney

To add tyo what FB just said, fix gear riders who keep slack in their chains know instantly any time they go from 100% driving to being "helped" by the momentum of the system. Good riders train to pedal all the way around and never see that slack until they are going downhill very fast. (In England in past years, racing was done on flat outdoor tracks, often grass, as handicap racing. Better racers would try to minimize leads to preserve their handicaps. Judges would watch theit chains and penalize them for "slack-chaining".)

There is a lot of wisdom in what Brian Ratliff said but the benefit from momentum when going hard isn't one of them. (I have done his 20 mph over the bars - my first ever fix gear ride; yes, the momentum is real but if we are racing and pedaling/powering circles, the momentum isn't helping. The concept of "float" is real. I've never seen or heard it said before, but I have been doing it for 40 years. What's really fun is riding to preserve a completely loose chain, no pull, no resistance. When I can do that, I know I've put in my miles.)

Ben

AlmostTrick

Thank you Brian for explaining it in a way that makes sense.

While it is true that under power the FG bike is not officially driving the cranks forward, (tension on the lower section of chain) it does even out the pedal stroke by aiding the momentum through the dead points of the crank rotation. So maybe instead of the power varying from "peak to near zero" as FB says, it remains more even in the FG system thanks to the flywheel effect.

This evening out of the power stroke seems like it would be beneficial to forward momentum by aiding crank speed even under power.

I believe this flywheel action Brian wrote about is what draws so many to riding FG. The rider becomes part of the system in a way that FW doesn't allow. I also believe it can be more efficient than coasting in plenty of situations.

FBinNY 

Sorry, but no.

There is no such thing as a flywheel effect. The wheel cannot drive the crank or in any way help it conserve momentum without transferring power from the upper to lower loop. Since it can't push, it can't help it conserve momentum or smooth out power.

ALL crank motion of a even slightly skilled rider is the result of his brain's motion control system and learned pedaling technique which works without conscious effort.

If the rider is incapable of maintaining a smooth always under power pedal motion, you'd hear the chain popping as the slack transferred back and forth between the upper and lower chords.

So, there is no such thing as a flywheel effect in a fixed gear system, but I know that some people cannot or will not free themselves of that notion.

So, try this experiment. Push the rear wheel forward a bit to establish more slack, say 1" vertical play at the center. Now ride and relax so you get to feel and hear the backlash whenever the wheel wants to push your feet. Once you have a sense of what it feels like, go ride. I guaranty you won't feel this at all, meaning the wheel is never pushing your feet, until/unless you're on a descent, or are slowing in anticipation of stopping.

If you're fairly new to riding, you may get that unwanted back;lash effect from time to time, and if so, can use it as a teaching aid to improve your technique until you don't have the problem any more. (should take about 1 hour, tops)

Trakhak

This thread reminds me of another forum in which discussions of fine points of audio amplifier circuitry are dominated by novices arguing against the reasoning of people who have been employed to design audio amplifiers for 40 years. (FBinNY, with his vast experience and relentlessly logical approach, would be in the latter category of debater.)

redfooj

FG makes it easier to track stand therefore FG wins

AlmostTrick

I knew you'd object to the flywheel effect and come freewheeling back to the thread!


I'm not talking about transferring power to the lower loop. Even while maintaining power on the upper loop, I can feel the cranks spinning through the dead points easier than it does with a freewheel. I'll bet you can too. Flywheel, momentum, whatever you want to call it. Why is that and what is it worth? Seems to me it aids spinning, which has to aid forward momentum.

wphamilton

What FB is trying to say, and he is correct, is that there is no difference except when the freewheel is coasting with the SS, or when you're braking with your feet with the fixed. No difference in efficiency of the bike, no difference in momentum, no difference in energy. A single speed functionally IS a fixed gear as long as our feet drive the pedals forward.

But you're forgetting coasting in other cases. Coasting around a corner for a trivial example. Posting over bumps. Actually I don't think FB is "forgetting" this but has the viewpoint that we can ride a single speed exactly as a fixed gear if we want, except in that one case of braking, and therefore a fixed gear cannot be a more efficient machine.

It's what I am trying to get across with
A freewheel doesn't force you to coast-push, which is "bad", but a fixed gear prevents it.

The other side of the question is does spinning your feet when you could be coasting cost you? Obviously yes, down-hill fast. Almost as obvious, yes on flat ground when you're slowing for example, because moving our legs up and down requires some effort as opposed to coasting which requires none. Evidently from this thread "How much?" is not so obvious. Angular momentum is something of a red herring, because the situation is not different between the bikes until your feet stop moving (or move slower with the freewheel than the pedals would move with the fixed gear). Your feet DO have angular momentum however (sorry guys, but they don't have to be "fixed" in orientation. Planets in orbit for example). A change in angular momentum will occur when you're coasting and speed back up, and it includes the mass of our feet, but it's minuscule compared to the linear momentum of the bike and rider. Not that important.

The reasonable thing to ask, IMO, is what is the cost if for example you pedal for three seconds, coast for three seconds and pedal again as opposed to just pedaling for six seconds, and travelling the same distance. The first is going to have higher peaks in speed, and that's going to cost in higher aerodynamic resistance, but again that's probably small enough to be another red herring. Otherwise, energy difference, basically none. Physiologically - a different story.

TLDR; just about ALL of it boils down to how you ride the bike!

prathmann

If you're maintaining tension on the upper part of the chain then the cog on the freewheel is constantly pushing on the pawls and keeping them in a fixed position. I.e. the freewheel is acting mechanically exactly the same as a fixed cog. The only physical difference is the miniscule increase in weight due to the ratchet mechanism and bearing of the freewheel.

The other difference is the psychological one of the rider in knowing that he can choose to coast at any time with a freewheel but not when he's riding fixed. If you "can feel the cranks spinning through the dead points easier" then it's due to this psychological difference.

FBinNY 

We have to separate perception from mechanical reality. You may "feel" the cranks turning past the dead spots better than with a freewheel, but is this really happening.

Keep in mind that, as I explained earlier, the rear wheel, sprocket and chain can't push the cranks around without the noticeable pop of the slack moving from the lower to upper loop. So, the rear wheel cannot be acting as a flywheel or in any other way helping the cranks turn more smoothly. It's all YOU using learned motion to keep the upper loop constantly tensioned to some degree.

I liken this flywheel effect (illusion) to descending a steep flight of stairs. We've all done this a number of times, and probably remember how using the banister helps. But do we actually use the banister, ie. grab it to steady ourselves, or do we simply keep our hand floating above it, and in doing so feel more secure and descend with more confidence?

wphamilton

Doesn't matter anyway, since whatever "flywheel effect" the rear wheel has, it would be the same whether or not it's connected to the pedals.

In fact, if you feel it it's because the pedals are pushing against your feet and that has the opposite effect of a flywheel - slowing the bike down.

popeye

The SO lost her pedals on a steep hill.

FBinNY 

Yes, but to be clear, by flywheel effect, I'm referencing the claimed effect of acting to somehow (don't ask me how) help maintain the momentum of the cranks.

Some fixed gear ture believers keep insisting that fixed gear has some advantage in helping to keep the cranks turning through the dead spots. That's what I'm disputing.

That said, pedaling smoothly is a learned process, and it's learned through "patterning" whereby a sequence of motions are recorded in the cerebellum, and then programmed for execution on demand. Riding fixed for a while can be an aid in developing a smooth steady pedaling style, which is good. But from there on in, it's all in your head (literally).

79pmooney

Yes, if you are pedaling poorly and letting the chain go slack at times. If you "feel the cranks turning" you are flunking Smooth Pedaling 101.

The cost is that you have to pedal twice as hard. For the same speed-, you have to do the same work/power expended over a time. But now you are only pedaling half the time, hence twice the power required. Power is force times distance/time. At the same RPM and cranks, the distance is the same, the time is now half and the force must be doubled.

Conceivably a person could train himself to be better at the half the time routine, but I wager that same person could average faster riding like the rest of us. (There are those half time pedals out there. None have ever made it to the pro ranks. Of course, this might just be shame from being laughed at so much.)

Ben

Bandera

Yep.
A FG machine is a teaching tool for smooth pedaling technique with a simple and robust feedback loop to condition response.
Zen Control and Being One with the Bike optional.

-Bandera