Gyroscopic Effect

[stapleking]

I read with interest Keith's recent missive regarding gyroscopic effect of wheels on a bike. He suggests, at least as far as the front wheel of a Kaw Z6R is concerned, there is little "effect" on turn-in.

 

I'm not sure that's right. For one thing, his admittedly inexact experiment doesn't seem to me to be measuring turn-in [or resistance thereto]. The gyroscope effect of the wheels turning in the fore/aft direction is to resist falling, or turning, in the lateral one.

 

The less mass one has rotating in the one direction, the less will be the resistance to turning [falling] in the other aligned 90 degrees to the direction of rotation. That is why great attention is paid to things like wheel/tire weight, other unsprung rotational masses, rotational masses in the motor, and so forth.

 

For example, everybody recognizes the benefit of lighter wheels; fewer understand that removing the charging system in the motor and lightening up the rotating drive line componetry has a similar effect.

 

Anecdotally, I can certainly attest to the dramatic improvement in turn-in quickness I experienced with my Buell when I put lighter forged wheels, removed the charging system, and fabricated a belt drive primary with dry clutch. Yes, some of the effect I noticed was most certainly due to overall reduction in bike weight, but the difference was too dramatic to be only that; I believe some of the improvement was reduced gyro effect.

 

So, Whaddaya' think boys 'n girls???

[fastfreddie]

regarding keith's self-proclaimed 'unscientific' experiment...how hard/quickly did he push on the bars?

[Balistic]

regarding keith's self-proclaimed 'unscientific' experiment...how hard/quickly did he push on the bars?

what would you be looking for Fred? What would speed of turning do to the force? It does show that the gyroscopic procession doen't do much.

Will

[stapleking]

Will,

 

I'm still confused; when Keith and you say the gyroscopic progression doesn't

"DO" much, what do you mean "do"?

 

Seems to me, to lean [turn] the motorcycle one must overcome the resistance [gyroscopic effect] of the bike to move from the vertical plane. The more gyroscope, the harder it will be to do this, i.e. more push on the bars. That's what overcomes the bike's tedency to remain upright - opposite lock push on the bars to force the bike to "fall in". Ergo, the amount of force required is proportional to the amount of gyroscopic effect [rotational mass]. It "does" a great deal........

[Balistic]

Will,

 

I'm still confused; when Keith and you say the gyroscopic progression doesn't

"DO" much, what do you mean "do"? 

 

Seems to me, to lean [turn] the motorcycle one must overcome the resistance [gyroscopic effect] of the bike to move from the vertical plane.  The more gyroscope, the harder it will be to do this, i.e. more push on the bars.  That's what overcomes the bike's tedency to remain upright - opposite lock push on the bars to force the bike to "fall in".  Ergo, the amount of force required is proportional to the amount of gyroscopic effect [rotational mass]. It "does" a great deal........

 

The deal is the gyro is resistance to turn is equal to it's resistance to go back to center, hence zero. What is turning the bike is the front wheel being driven out from under the bike, the opposite direction to the lean. If you had the bike going down a strait line and turned left the front tire would first go over the right side of the line ( CS,BS no matter).

My point is with wheel on the ground all the gyro does is have resistance to turning, which can be easily overcome with the bars. The self centering has much more to do with trail than the gyro.

Will

[stapleking]

OK - I THINK I've got it......

[fastfreddie]

when trying the spinning bicycle wheel experiment, not much drama is created if you go slow and easy. if you try to 'wrench' that thing like you were flickin' it into a turn, it twists guite aggressively but, apparently, with no more range of motion than if pushed easily. so...if the motorcycle wheel is spinning and you casually push(finger pressure) on the bar, nothing dramatic happens...not to mention, the wheel's ability to apply countering force is dampened by the weight of the bike itself. if, however, you crank on them bars like your life depended on it, don't you think the bike would, figuratively, jump off the stand?

(let's assume a equal force on each bar and not upsetting the balance of the bike with our direct inputs).

that's what i was lookiing for...

[Balistic]

when trying the spinning bicycle wheel experiment, not much drama is created if you go slow and easy. if you try to 'wrench' that thing like you were flickin' it into a turn, it twists guite aggressively but, apparently, with no more range of motion than if pushed easily. so...if the motorcycle wheel is spinning and you casually push(finger pressure) on the bar, nothing dramatic happens...not to mention, the wheel's ability to apply countering force is dampened by the weight of the bike itself. if, however, you crank on them bars like your life depended on it, don't you think the bike would, figuratively, jump off the stand?

(let's assume a equal force on each bar and not upsetting the balance of the bike with our direct inputs).

that's what i was lookiing for...

Yes, But what is the point. I would concede that the gyroscopic effect increases with speed and it is still overcome the same way, with the bars. It's not just the gyro that increases the steering effort, There are two others that don't want to turn either, engine and rear wheel.

Will

[fastfreddie]

i see what you're saying...

so, it doesn't matter how much gyro procession can be generated with the front wheel. it's not enough to be of any significance when balanced out by the other rotating masses?

[Balistic]

i see what you're saying...

so, it doesn't matter how much gyro procession can be generated with the front wheel. it's not enough to be of any significance when balanced out by the other rotating masses?

Not really what I mean. The force from the front wheel is mirrored when you release the steering input. What im tying to say other than that is that if the tire is in contact with the groung the gyroscopic procession isn't doing anything to turn the bike, it's only contribution is to resist it.

If however you are comming out of a corner and the front comes up wile your still leaned over the gyro can be used to effect a small change, and under certain conditions may be enough to finish standing the bike up.

Will

[fastfreddie]

ok...so, it doesn't matter how much gyro procession can be generated with the front wheel...it has negligible effect on turning the bike?

 

please say yes or i'll be forced to assume it's a left coast/right coast failure to communicate.

[CBRKeith]

I think it's got to be a combination of both gyroscopic precession and out-tracking that turns a motorcycle. When you press on the handlebars, it makes the front wheel turn slightly. The gyroscopic precession, along with the front tire contact patch moving out from under the bike, causes the motorcycle to lean. As the motorcycle leans, the gyroscopic precession causes the front wheel to steer in the direction of the lean. That's what allows us to become a passenger after countersteering, while the motorcycle rails around the turn without any additional input into the handlebars until it's time to pick it up.

 

The gyroscopic effects of the wheels are why the manufacturers strive to make the frames so rigid torsionally. Flex in the frames was a principal contributor to the wobbles so common in older motorcycles when turning at high speed.

 

A better demonstration of the true effects of gyroscopic precession on the motorcycle is when motocrossers cross it up as they get big air. That is done by simply turning the handlebars. In that case there is nothing other than the inertia of the machine to resist leaning/rotating.

[Balistic]

I think it's got to be a combination of both gyroscopic precession and out-tracking that turns a motorcycle. When you press on the handlebars, it makes the front wheel turn slightly. The gyroscopic precession, along with the front tire contact patch moving out from under the bike, causes the motorcycle to lean. As the motorcycle leans, the gyroscopic precession causes the front wheel to steer in the direction of the lean. That's what allows us to become a passenger after countersteering, while the motorcycle rails around the turn without any additional input into the handlebars until it's time to pick it up.

 

The gyroscopic effects of the wheels are why the manufacturers strive to make the frames so rigid torsionally. Flex in the frames was a principal contributor to the wobbles so common in older motorcycles when turning at high speed.

 

A better demonstration of the true effects of gyroscopic precession on the motorcycle is when motocrossers cross it up as they get big air. That is done by simply turning the handlebars. In that case there is nothing other than the inertia of the machine to resist leaning/rotating.

This is actually very simple. The gyro is just trying to stay where it is and you have to make it turn, then when you release the bars the trail snaps it back in line with rear. so any gyro force that was produced when you turned is canceled when the it snaps back in line, sum effect = 0.

if you think a bike wont turn without a gyro you don't have to look too far to find out it will. You can get a ski for dirt bikes so they can be ridden in the snow, they turn. Remember the wet bike? It was like a bike and a jet ski mix, they CSed and had no gyro.

 

One other point: If the gyro was so important to turning how do lighter wheels allow the bike to turn better?

Will

[fastfreddie]

now it all comes clear to me...call bs if i got this wrong.

if my 426 is in the air, turning the bars(crossin' up) does not put me into a whip. a mild leaning(a few degrees?) off perpendicular occurs and then, when the bars are returned to center, the bike goes vertical again. (same idea will was talking about when exiting a turn with the wheel in the air but, i believe you'll be steering from the other direction). whipping it is something initiated before the bike leaves the ground so, by extrapolation, gyro procession has little to do with the physics of steering the bike. it's merely a coincidental side effect of little account when weighed against the dynamics involved with steering.

 

these dynamics would be dictated by the steering geometry, down to and including the profile of the tire; the rider's input and gravity. take a bicycle, for example. at rest, turn the bars to the right. now, push the bike forward along its longitudinal axis. what happens? the wheel, already off center from the axis, tracks further off line to the right as gravity pulls the bike down or leans it to the left. at the same time the bike starts leaning, the wheel starts swinging its track to the left(geometry) and the bike turns to the left. obviously, this only demonstrates the motions that result from countersteering. there was no gyro procession to speak of...

 

One other point: If the gyro was so important to turning how do lighter wheels allow the bike to turn better?

Will

by 'better', i take it you mean 'quicker/easier'? with less mass comes less gyro effect. therefore, that effect, its desire to stay where it is, is overcome more readily by the rider's counter-steering input, gravity and the bike's inherant handling qualities(geometry).

 

odd ramblings that pose other questions...

one day, in pictures of my bike hard in a turn, i noticed the front wheel was actually pointed in the direction of the turn. i looked through a lot of similar pics and saw the same thing in all of them.

in shots of corner entries, it seemed up until the time i was actually finished c/s-ing, the wheel was in the 'counter' position.

(the above observations are in line with will's comments and my epiphany. thanks for getting me here, guys).

this transition from 'counter' to whatever you want to call it when the wheel points into the turn, is a moment of severe loading on the tire. do the bicycle experiment...you'll feel it.

so, on to the questions:

could this be the moment where riders 'inexplicably' lose it?

is this 'hook' the event that marks the actual beginning of the turn? (assume a 'no brake' entry).

being aware of this moment, can we use it to our advantage, even if for no other reason than being aware of it?

perhaps, with experience, we can incorporate it into our turn 'timing'?

 

whoa...reading and re-reading those questions(you know, gotta do that proofreading on a long post like this), they sound more and more rhetorical.

thank you, keith, for providing an outlet for us. i never think this much about it, riding, on my own.

am i on the right track? (no pun intended).

[JohnnyRobshaw]

John Robinson was the English tech journalist ( he died in 2002 I think) and I found this quote on the net ( in an ad for light wheels). I vaguely remember the original article and will try to find it- He wrote for 'Bike' magazine.

 

First, a quote from John Robinson in his "Motorcycle Tuning: Chassis" book:

"The wheels and various things attached to them are critical to the bike's performance. The masses of these parts have rotating inertia which has to be increased or decreased whenever the bike is accelerated or braked: it is unsprung mass, and therefore governs how the suspension performs; it is steered mass which affects the steering response and creates gyroscopic forces which interact with the steering. Every pound of material carried on the wheels is worth two to five pounds carried elsewhere on the bike"

[Balistic]

now it all comes clear to me...call bs if i got this wrong.

if my 426 is in the air, turning the bars(crossin' up) does not put me into a whip. a mild leaning(a few degrees?) off perpendicular occurs and then, when the bars are returned to center, the bike goes vertical again. (same idea will was talking about when exiting a turn with the wheel in the air but, i believe you'll be steering from the other direction). whipping it is something initiated before the bike leaves the ground so, by extrapolation, gyro procession has little to do with the physics of steering the bike. it's merely a coincidental side effect of little account when weighed against the dynamics involved with steering.

I did one moto school and got the pleasure of a pro passing me a number of time in a section of jumps that was in an arc. I would jump land turn, he was turning off the face of the jump and whipping the bike into position for the next turn. I watched him several times to confirm it, and then asked the instructor if what I thought I saw was it. He did confirm the steering for a whip is on the face, but the only way to recover it is the gyroscopic procession.

Will

[fastfreddie]

are you saying it's not necessary to pick the bike up with your body before/for touchdown?

[Balistic]

are you saying it's not necessary to pick the bike up with your body before/for touchdown?

first off I can't do this, so anything I have to say about it is just an observation. I think it's all the gyro. You are committed with you body and can't change after you leave the ground, You can move but the bike will do the opposite of what you do. If you bushed it down you could pick it up, but to fix the steering you did off the face you will need to use the gyro.

Will

[TheJonesBoy]

It seems a lot of you are not familiar with bicycle steering physics. Here is a quick primer.

 

Balance is maintained when your center of gravity is between the two contact patches of your tires. When your CG moves to either side of the line drawn between the patches, you fall in that direction. On all bikes, the handlebars are at an angle, and the axis of steering (a line through the handlebar pivot) falls in front of the contact patch of the tire. These two parameters give you stability. As you fall to either side, the bike steers in that direction. This is why you can ride a bicycle with no hands (NOT GYROSCOPIC PRECISION!) If you don't believe this, take a beater pedal bike and weld the steering in the vertical position and try to ride it. You won't go more than a few feet, gyros or not. Other people researched this too. Some guy named David Jones, many years back, made a bicycle with a counter-rotating wheels whose gyroscopic forces all canceled out. It made only slight differences in handling characteristics but was completely rideable.

 

In order to turn ANY bike (pedal, motor, or otherwise) you must turn in the opposite direction of the turn. When you do this, the bottom of the bike moves (as thats where the contact patches are) one way, bringinig your CG to the opposite side, and initiating a fall which can be used to initiate a turn. On a motorcycle with big tires (compared to a pedal bike) one maintains the countersteer during a turn. This is because of the contact patch. During a countersteer turn, the tires touches the road closer to the sidewall, and leaves the road closer to the centerline. This gives you an actual steering angle which is different than the direction the tire is spinning. As you turn even harder, the rubber tire begins to distort. This distortion rolls the tire sideways, adding to the effects of the countersteer. One must countersteer less to maintain the turn. You also have inertia (centripital force) pushing you out of the turn, gravity and lean pulling you into the turn, chassis flex making your rear wheel turn, bump torque, etc. all going on too.

 

Gyroscopic precision may firm up the steering at high speeds, but it is minimal in comparison to the other forces at play (like gravity), and because it has really crappy leverage to work with (think about how wide the struts are). Imagine 50lbs pushing up on 1 fork strut and pulling down on the other (100lbs net force). I could counter that by moving my fat butt over an inch. Its nothing in comparison to the pull of the mass of the engine at a 30 degree lean angle, or the interia pulling you upright under the same conditions. Thats hundreds of pounds with feet of leverage! Lightening suspension and minimizing unsprung weight will help acceleration because it all acts like flywheels, damping acceleration. It will improve suspension response because there is less vibrating mass to dampen when you hit a bump. Removing sprung weight only makes a difference if it is a lot of mass (think percentage of bike+rider), and for many people the biggest, cheapest gains in this department can be had going on a diet.

[Eyespy]

As I have stated in the R1 forum lengthy and technical discussion on CS vs BS, additional evidence that gyroscopic precession is inconsequential to steering a motorcycle can be found in the common experience that lighter wheels/tires (which have a lesser polar moment of inertia) are easier to steer, despite the fact that by virtue of their decreased rotational mass and polar moment of inertia, they exert a lesser gyroscopic precession force on the vertical axis to lean the bike over.

[AndyIbbott]

Holy S%$t!

 

I was never into physics at School and I'm not really now but this thread is brilliant.

 

We did an experiment here in the UK with a pencil video camera mounted on the tank of an R1. Our Chief Instructor, Johnny Haynes then rode this R1 across a paddock turning the bike quickly from one knee to the next as quickly as he could.

The handlebars moved 5-7mm at the switchgear. No wonder it's hard to define!

 

All I know is this:

 

I push the inside bar right, I turn right.

Once the bike is turned (pointing where I want it to go) I stop the input and the front wheel turns in slightly to track the arc I have set.

 

Not a lot of physics but it works!

[Bones]

Andy, I?m with you mate.

 

If you listen carefully, as you scroll down the message thread, you can hear the can of worms opening.

 

I?m gunna stick to the ol? press-n-release. Its working quiet nicely, thank-you very much.

[racer]

Thank you to the anonymous guest I found reading this thread on the last click list. TheJonesBoy's primer is awesome and touches on several recent discussions we've had here about the physics of contact patches and gyroscopic precession. Balistic's posts are relevant, too. Great stuff!

 

Although none of the current threads are discussing this specific subject(s), there is at least one "physics" thread at the moment, and, I felt some of us might appreciate and benefit from it.

[racer]

What happened to Willie's posts in this thread?

[fossilfuel]

Hi Racer,

It has been a while since last I graced the pages but I had to......comment here! Stop the madness!

 

" The gyroscopic effect of the wheel during cornering is manifested by a righting moment. To counteract the gyroscopic effect of the two wheels and thereby maintain equilibrium, the rider can lean into the turn in such a way that the resultant of the weight force and the centrifugal force generates a moment equal and opposite to the gyroscopic moment of the two wheels. The rider can achieve equilibrium without displacing his trunk in order to produce a displacement of the mass center towards the inside curve but the lean angle will be greater than the ideal roll angle calculated on the assumption that the gyroscopic effect is zero.

In this case, the righting moment generated by the centrifugal force an the moment generated by the gyroscopic effect are both offset (thank you Will!) by the overturning moment of the weight force.."

Vittore Cossalter

 

Now can we discuss something that will help me get around the track faster?