Pillar of Wisdom - Gyroscopic forces...not

[Johan Bornman]

Cold Sundays are great for catching up on reading. I used yesterday as an excuse to finally read the official Sani2C magazine. Good thing I didn’t look at it before the event otherwise I would have stressed over that floating ocean bridge and fell in. Ignorance prevented me from fearing it and falling.

Nevertheless, an article in the magazine perpetuated an old myth and needs to be

 

addressed before it becomes a meme. It may be too late. More than a thousand people could have read it and taken it as gospel. But let me try and limit the damage.

The article was about skills improvement and contained three sub-headings as “Pillars of Wisdom” 1,2 and 3. Pillar 3 is the one in question.

Sean Badenhorst wrote:

 

“PILLAR OF WISDOM 3:

 

Momentum is your friend. The gyroscopic forces generated by your bike’s wheels turning increases the faster you are moving. This means the greater, your momentum, the greater your stability. That’s why, when you slow right down, you become wobbly and unstable. By just maintaining a little momentum you will stay upright. This is usually most common on steep climbs. To maintain your momentum on a steep climb, do a few ratchets with your cranks, using your strongest leg. This keeps the wheels moving and gives you enough time to catch your breath and return to your normal full pedaling action.”

 

The gist of my problem with this meme is that bikes don’t balance through gyroscopic forces. Although a bicycle wheel that turns generates a gyroscopic force, it doesn’t have anything to do with balance. I’ll explain its effect later. First, let’s examine how bicycles balance.

 

Bicycles balance in two modes, separated by a critical velocity (speed).

 

Mode One is when you are riding fast enough so that you balance by steering into the fall (it will become apparent soon) and Mode Two is when you’re going so slow that you’re effectively doing a track-stand. Those of you who can track-stand will know that those skills differ completely from balancing when riding. Actually, those of us who can’t track-stand know it even better.

 

Mode 1: Riding above the critical velocity. This is your most common riding mode when you’re pedalling along comfortably and not even thinking of balancing. Since a bicycle is laterally unstable without your brain’s help, you are constantly falling to the left or to the right – you don’t even realise it – and correcting the fall by steering into the lean. This brings your centre of gravity back underneath you and you don’t fall. Picture this by balancing a broomstick vertically on your hand. As the stick falls to the left, you move your hand to the left, which brings the centre of gravity underneath it again. Ditto for right, forwards and backwards. The broomstick has one extra plane into which it can fall – forwards and backwards. On your bike it is simpler, you don’t fall forwards or backwards, just left and right. Unicycles excluded from the previous statement. .

 

Back to the real-life bike at normal speed. You pedal along an continually sway left and right. Demonstrate it to yourself by looking at your wet tyre tracks. Prove that you cannot ride absolutely straight by trying to follow a road line for a length of time. Your luck runs out within ten meters or so.

 

Mode 2: Riding below critical velocity. This is where the article in question attempts to give advice. It acknowledges that it is difficult to balance at low speed but attributes it to low gyroscopic forces. The real reason is that at those low speeds you can’t move fast enough to steer your centre of gravity to underneath the “fall”. Indeed, the terrain may even prevent you from steering, like when you’re riding in a deep rut with no room for sideways movement. How a skilled rider balances in these conditions is to move his/her body laterally over the bike in an attempt to correct the lean – track-stand style. This requires core muscle strength similar to what’s required when you’re standing on a balance ball.

The author suggests that ratcheting will somehow wind up the gyro and get you to balance again. This is false. Either you increase the speed so that you can steer by “falling” or you balance Mode 2 style. He erroneously suggests that momentum creates stability through gyroscopic action. I don’t see how ratcheting would help in either of these two modes other than introduce some body movement which may help you to balance (Mode 2 style). Ratcheting produces no momentum and refutes his own argument.

 

So where does the gyroscopic force play its role in steering?

 

It automatically turns the front wheel into the direction you’re leaning as you go around a corner. Cyclists and motorcyclist instinctively know that to turn right, you lean right and left, you lean left. We don’t turn the handlebars, they somehow turn themselves, we just lean.

To understand this you have to remove your bike’s front wheel and experience the gyro forces first. Hold the wheel in your dominant hand by the skewer. It helps to straighten the skewer lever and hold that in your hand (swivel side to go fore-aft so that it gives you a sturdy handle in your hand. Put your forefinger on the jamb nut and spin the wheel with your other hand. The wheel should now spin in your hand and you’re holding only onto one side. Now “lean” the wheel like you’re turning and you’ll see the wheel forcefully steering into the lean. On the back wheel those forces are lost in the frame but in the front, it cause the bike to steer.

 

You may also want to convince yourself that at slow speeds the wheel doesn’t produce the same forces and that ratcheting the crank will do nothing to produce a gyro and do nothing to create momentum, only some perhaps-useful body movement like the sideways shaking a tight-rope walker with produce to maintain balance.

 

Further proof (just in case you’re still confused) that a gyro has nothing to do with not falling over is that you can reduce the size of the wheel to a point where it has no gyro effect even at great speed , like on a little skateboard-wheel scooter. It still steers by moving underneath the fall. Then go even smaller, an ice skate. It also steers by moving your legs under the fall – there is zero gyro in that scenario but the method of steering is always the same.

Edited June 10, 2013 by Johan Bornman

[BergForce]

Here is a question:

 

If gyro has no effect, if you remove the rider from a bicycle going at 50km/h, it will travel much further without the rider than a bike with no rider travelling at 10km/h. Is this only down to speed or does the gyro effect help to keep the bike going faster upright for longer?

[Johan Bornman]

Here is a question:

 

If gyro has no effect, if you remove the rider from a bicycle going at 50km/h, it will travel much further without the rider than a bike with no rider travelling at 10km/h. Is this only down to speed or does the gyro effect help to keep the bike going faster upright for longer?

Please rephrase. I'm not sure what you mean.

[brussel]

Bergbok, I was about to ask the same question.

 

I suspect the gyro effect helps, but that it is very small compared to other effects such as steering etc. but if you jump off the bike, it must help to an extent

[BergForce]

Please rephrase. I'm not sure what you mean.

 

Sometimes when a motorbike rider falls it seems the bike can travel a very long distance without the rider on the bike. The higher the speed the longer the bike will stay upright with no rider (no steering balance).

[DJR]

I'm going to believe Johan for now and keep an eye on this thread.......

[Johan Bornman]

O

Sometimes when a motorbike rider falls it seems the bike can travel a very long distance without the rider on the bike. The higher the speed the longer the bike will stay upright with no rider (no steering balance).

OH, ok.

 

Well, firstly, the higher the speed, the more energy the bike has and the further it will travel irrespective of whether it is upright or not.

 

What you describe here has a nice Youtube video of a guy that pushes a riderless bike forward and it stays upright for a remarkable distance. There is a small tendancy for the giro to keep it upright if the bike's weight and the wheel's weight doesn't have a large disparity. With a rider, I suspect the effect is nulled.

[BergForce]

[Johan Bornman]

I'm going to believe Johan for now and keep an eye on this thread.......

You sound like the guys in the Atheism/religion threads. Never just believe. Question, experiment, investigate, make up your own mind but allow it to be modified by other viewpoints when need be. Go play with a broomstick and see if you get it.

[Pappa Bear]

Ever tried riding with a seized headset? It is impossible to stay upright.

 

Try balancing your bike on its BB and spin both wheels...... See if the bike stays upright.

[Skott5]

http://www.youtube.com/watch?v=n9sLFZpOSZg

 

lol, thats awesome !!

[Johan Bornman]

 

 

Try balancing your bike on its BB and spin both wheels...... See if the bike stays upright.

 

Yes, good point. This will be a good experiment to test the pure gyroscopic effect so much vaunted about.

[Robrider]

Ha, I love these posts of yours Johan. It has been a while.

 

I agree with you on 99% of it. I agree gyro forces play no role. I disagree with what you said about gyro effects in the corner. The gyro effect has an initial effect as you lean. But once the wheel is "leaned" the gyro effect stops. This to me means that in a long corner you would have trouble steering. I think gyro has little to no effect, even in a corner.

 

To answer bergboks question, I think it comes down to stability of the bike design. For example, when you turn a corner in your car and let go the steering wheel, it automatically straightens out. I think this effect keeps a bike upright. As the bike leans to fall over, the bars tilt into the corner and self correct the balance.

[patches]

O

 

OH, ok.

 

Well, firstly, the higher the speed, the more energy the bike has and the further it will travel irrespective of whether it is upright or not.

 

What you describe here has a nice Youtube video of a guy that pushes a riderless bike forward and it stays upright for a remarkable distance. There is a small tendancy for the giro to keep it upright if the bike's weight and the wheel's weight doesn't have a large disparity. With a rider, I suspect the effect is nulled.

 

hmmm... interesting. I see your point in your first post.

 

Especially concerning the "gyros playing effect from ratcheting on slow technical climbs"... I agree that is far fetched.

 

But as for the rider weight thing... that got me thinking.

 

Firstly about this

 

 

(I remember a similar setup in the science exhibition at Gold Reef City)...

 

and then about the real life application (not quite the one Mr Badenhorst or yourself are referring to, but one I encounter from time to time)...

 

When jumping, one can feel the effect of the gyro. Especially at speed. The faster one goes, the more laterally stable the bike itself is (remembering that there is no contact with the ground to offer friction which prevents the weels from moving side-to-side).

 

Then add a trick like a whip or X-up. By changing the orientatoin of the front wheels axis (ie. not perpendicular to direction of "flight" anymore). Do an X-up slowly and it will pull the whole bike off plane.

 

So yeah, I think gyroscopic forces do definitely play a role in keeping a bike in a certain plane. but at slow technical climbing speeds... they're almost negligable and like you say, a track-standing type of balance will be far more beneficial.

[Johan Bornman]

hmmm... interesting. I see your point in your first post.

 

Especially concerning the "gyros playing effect from ratcheting on slow technical climbs"... I agree that is far fetched.

 

But as for the rider weight thing... that got me thinking.

 

Firstly about this

 

https://www.youtube.com/watch?v=eLRFsy0fOTE

 

(I remember a similar setup in the science exhibition at Gold Reef City)...

 

and then about the real life application (not quite the one Mr Badenhorst or yourself are referring to, but one I encounter from time to time)...

 

When jumping, one can feel the effect of the gyro. Especially at speed. The faster one goes, the more laterally stable the bike itself is (remembering that there is no contact with the ground to offer friction which prevents the weels from moving side-to-side).

 

Then add a trick like a whip or X-up. By changing the orientatoin of the front wheels axis (ie. not perpendicular to direction of "flight" anymore). Do an X-up slowly and it will pull the whole bike off plane.

 

So yeah, I think gyroscopic forces do definitely play a role in keeping a bike in a certain plane. but at slow technical climbing speeds... they're almost negligable and like you say, a track-standing type of balance will be far more beneficial.

I'd like to respond but quickly educate me on a X-up and whip?

[patches]

Ha, I love these posts of yours Johan. It has been a while.

 

I agree with you on 99% of it. I agree gyro forces play no role. I disagree with what you said about gyro effects in the corner. The gyro effect has an initial effect as you lean. But once the wheel is "leaned" the gyro effect stops. This to me means that in a long corner you would have trouble steering. I think gyro has little to no effect, even in a corner.

 

To answer bergboks question, I think it comes down to stability of the bike design. For example, when you turn a corner in your car and let go the steering wheel, it automatically straightens out. I think this effect keeps a bike upright. As the bike leans to fall over, the bars tilt into the corner and self correct the balance.

 

Part of the reason that braking in a corner makes a rider unstable is that this fights the gyroscopic forces that are in play. When this deceleration happens suddenly (like when braking) the wheel will want to "stand up" and this greatly affects the stability of the rider throuhg a corner.

 

Note: when I say corner, I'm talking about really fast bermed cornering with the implementation of countersteer.