In addition, big wheel on the same fork angle means longer trail. Longer trail helps stabilize a bike.

Quote from MagicFr :

If you add slip angle in front wheel by turning bars left, you generate a big lateral force. you turn bars left, you create a big left force, as contact patch is below gravity center, it create a big torque, wich lean the bike to the right ( counter steering ).
At stationary, tire forces is NULL, no lateral force to help you.

Just asks Vehicle Physics is my job

That's interesting. I'm sure of two bikes, one without gyro forces and one with, the bike without would be constantly trying to fall over, and even though keeping upright would be perfectly possible, surely you'd have to be much busier with the steering, even if the inputs would only have to be tiny, repeatedly and quickly steering just enough the way the bike's falling so that it doesn't fall further. I'd imagine it would be hell in a crosswind

The cg height thing is also interesting. I suppose it's like balancing a long stick on your finger - the longer it is the easier it is to balance, because it falls more slowly, but then if begins to fall you also would have to move your finger further in order to restore balance again.

Bigger bikes also weigh more, which means less leverage from a same rider.

I've read that the spinning internals of a motorbike's engine will help keep it upright at low speeds, so keeping the revs up and slipping the clutch (with rear brake if needed) is how to go about creeping.

As for bicycles, trackstanding is not difficult--especially with a fixie.
http://youtube.com/watch?v=BkkTSVVrPYk Ain't no gyro effect there!

Cool vid.

Quote from Bob Smith :

Cool vid.

:spam4:

Quote from wark :

As for bicycles, trackstanding is not difficult--especially with a fixie.

i challenge you to do it for a prolonged time then ... its nowhere near easy imho

If you practice it long enough it's easy, I can stand like this for a long time before I get tired.

Quote from Bob Smith :

Cool vid.

+1, crazy Germans!

Ooo, another physics discussion

Gyroscopic forces work a little differently than most people think. When a bike/motorcycle begins to tip to the side (roll, ignoring steering here), the gyro torque actually causes a yawing torque on the bike which twists it into the corner, much like steering on a car. At the same time, if you were to yaw the bike through steering, the gyro effect exerts a roll torque that tips you into the corner. This is probably why when riding straight, you don't have to steer left to tip the bike to the right (at least not on my friend's Harley ), then steer again to the right to make a right turn. Just steer right and it rolls into the turn all by itself, no countersteering required at all. I'm very far from being anything remotely close to an experienced rider, but this is what my experience was on that one bike. And when it came time to straighten up the bike again I could just steer it straight without giving a quick input to the right in an attempt to kick the bike upright or do some fancy weight shifting with my behind. Without the gyro effect I suspect this wouldn't work so well.

In a car the effect is similar. When you steer the wheels or the car is rotating to the right in a turn, the gyro effect causes the car to roll into the corner slightly, reducing weight transfer from what the regular steady state calculation would say it should be. The quicker you steer or the quicker the car is rotating, the greater the roll torque (it must be so to conserve angular momentum). This is generally an understeer tendency and therefore a stabilizing effect.

I do gyro in my sim and although I haven't tried it without it in the full sized cars in a very long time, the difference with and without gyro in Virtual RC Racing is very noticeable. Enough to where you'd go back to the setup screen and tweak the car a bit to get the balance back how you had it before. Maybe it's not so much on a 1:1 scale car, I don't know

A few years ago I did some calculations for a motorcycle to see if the effect would be significant for upright stability. The resulting torques were so large I thought I'd made a mistake and rechecked it several times, but it was quite significant even at highway speeds. On a bicycle it would be much lower of course since the moment of inertia of the tires is much lower, as are the rotational velocities.

There is more to the picture of stability of course, such as the other effects mentioned earlier by others (fork angle, etc.), but this is how the gyro effect by itself influences things.

Gregor Veble tried a motorcycle in his engine a few years back. If I recall correctly (this was a long time ago) he found he could make the bike work and be pretty stable without the gyro effect, but gyro helped it quite a bit. I'll have to ask him about it again when he's online next.

todd shouldnt a gyro roll to the left if you steer it to the right ? at least thats what my pro gyro testing rig (spinning a cd on my fingernails) tells me

Quote from Shotglass :

i did ... with the bf1 having the speedo at ~800 ... no noteworthy effect

Spinning the wheels at a constant velocity isn't going to create any noticable effects. They need to be accelerating.

my point was that i got the bf1s wheels up to ~800 and did brake them down agaon to 0 as quickly as possible without any effect

Quote from Shotglass :

i challenge you to do it for a prolonged time then ... its nowhere near easy imho

I'm a cyclist. I bike ~200 kilometers a week. I use clipless pedals. We do have red lights in my country, too. Notwithstanding (pun intended), if you want me to hold a camera while I do it, forget it!

What he said.. it's not that hard. I can do it as well as the athletes on that video with a mountain bike. The really good people do it with those bikes on the edge of high bridges, etc, the same as trial bike athletes do.

surely it did take you a while to learn it didnt it ?
just because its easy for you now doesnt mean its an easy skill in general

I couldn't tell you.. I've been able to do it for at least ten years. I would say it's at most half the difficulty of learning to ride a bike. You just go slower and slower.
If you put your mind to it, an hour everyday will teach it to you within a week or so, I think.

I don't think thin-spoked bicycle wheels make for significant enough gyroscopes. I am pretty sure motorcycle wheels have a considerable gyroscopic effect. If I recall right, racing motorbikes have more to gain than lose in reducing their wheels' mass. I'm pretty sure I've read someone who was racing at club level say that going from stock wheels (on an Aprilia RSVR) to carbon fiber wheels made steering inputs considerably easier.

The rims in LFS (again IIRC) are calculated on the fly so that Bespoke causes sync errors. It's odd that rims' weight would be accounted for to such precision, but not their gyroscopic force if that force is as significant as jtw62074 describes.

Its silly to claim that it is "easy" to stand with a bike in balance, unless you wave your hands around and have a thoroughly corrupt definition of easy.

Also, while gyroscopic effects aren't dominant in keeping the bike upright, they certainly create some large forces when the axis of the wheel is rapidly accelerated. I'm guessing without further knowledge that its a factor considered in the design of the axles and bearings of bikes, and I'm also guessing that particularly in motorbikes these effects alter handling qualities significantly.

Quote from Shotglass :

todd shouldnt a gyro roll to the left if you steer it to the right ? at least thats what my pro gyro testing rig (spinning a cd on my fingernails) tells me

Depends on which way one spins the CD.

Quote from Shotglass :

todd shouldnt a gyro roll to the left if you steer it to the right ? at least thats what my pro gyro testing rig (spinning a cd on my fingernails) tells me

Shouldn't be, no (if you spin it away from you, at least). Although I tried the same thing with a CD on a pen just now it would seem that's right. There's some friction involved there though

This is a nice animation showing it:

http://en.wikipedia.org/wiki/I ... scope_wheel_animation.gif

The wheel is spinning "forwards" at the top into the picture as though you're behind a wheel rolling away from you. They roll it to the left which yaws it also in the same direction. Same thing happens if your input torque is to yaw the wheel. It rolls/banks into the turn.

What should be noted is that there is only a gyroscopic effect if the wheel is both spinning and rotating about another axis. I.e., when travelling straight down a road there is no gyroscopic torque at all. Introduce the slightest yaw/roll velocity and the reaction will appear.

Quote from Breizh :

The rims in LFS (again IIRC) are calculated on the fly so that Bespoke causes sync errors. It's odd that rims' weight would be accounted for to such precision, but not their gyroscopic force if that force is as significant as jtw62074 describes.

To be fair though, I don't know if it's significant on big cars. With the little RC cars in Virtual RC it makes quite a difference, but those may very well be totally different from regular sized cars. There are quite a lot of vehicle models used in handling engineering that don't bother with the effect either.

EDIT: Here's an interesting video showing a rather bizarre gyroscopic effect

http://www.metacafe.com/watch/ ... _gyroscopic_effect_weird/

Cool vid. I remember reading a paper on those shapes with odd behaviors at one point. The wikipedia article says sometimes the bases are completely symetrical but the mass distribution is offset.

Quote from jtw62074 :

To be fair though, I don't know if it's significant on big cars. With the little RC cars in Virtual RC it makes quite a difference, but those may very well be totally different from regular sized cars. There are quite a lot of vehicle models used in handling engineering that don't bother with the effect either.

also rc cars turn quite a lot faster so the effect might be more pronounced

that animation has got me confused and i dont get why my cd behaves exactly in the opposite way
also spinning the cd at different speeds seems to make the effect more or less pronounced indicating that it really is a gyro effect rather than something else


EDIT:

i just figured it out ... the animation does agree with the cd experiment
you have to keep in mind that the input axis is the green one and blue is the output axis not the other way round
so in our motorcycle example the bike would drive upwards and you steer it round the green axis

Quote from skiingman :

Its silly to claim that it is "easy" to stand with a bike in balance, unless you wave your hands around and have a thoroughly corrupt definition of easy.

Also, while gyroscopic effects aren't dominant in keeping the bike upright, they certainly create some large forces when the axis of the wheel is rapidly accelerated. I'm guessing without further knowledge that its a factor considered in the design of the axles and bearings of bikes, and I'm also guessing that particularly in motorbikes these effects alter handling qualities significantly.

Depends on which way one spins the CD.

Okay, it's really difficult. Feel better?

Quote from jtw62074 :

At the same time, if you were to yaw the bike through steering, the gyro effect exerts a roll torque that tips you into the corner.

You got the effect in reverse. Steering in one way rolls you in the other.

Suppose you're traveling forward, so the front wheel's angular momentum points left. You "steer" to the left by exerting a torque, whose direction points up. The change in the wheel's angular momentum is then in the direction of the torque, which is up. The originally left pointing angular momentum then points left-up, rolling you to the right.

Steer (yaw) left -> roll right. One more reason to countersteer.

Suppose your bike begins to fall to one side: rolls left. The torque that the bike exerts on the wheel points aft. The left pointing angular momentum then points left-aft, yawing the wheel to the left.

Roll left -> yaw left.

You see, that the gyro is "stable" arises from this alternating force and response: yaw left->roll right->yaw right->roll left.... If you had "yaw left->roll left" like you said, then the gyro goes yaw left->roll left->yaw left even more->roll left even more... until it diverges.

Oh, and please read the second part of this article already posted:

Quote from StewartFisher :

No. Have a look at this page made by one of my university lecturers:

http://www2.eng.cam.ac.uk/~hemh/gyrobike.htm

He's quite a character...it's amazing how someone can get so excited about spinning things.
Strictly speaking the gyroscopic forces do have an effect but it's very small, and it is dominated by other effects.

Starting with: "It is almost certain that gyro effects ..." you'll find that he says exactly the same thing I said.

hi todd,

well, it's true gyro effect help,didnt said opposite but what you said is a bit in opposite of what i read( about torque generated ), but maybe it was a paper about bikes and not motorbikes. There was no number in that parer.

Anyway, even if gyro on heavy wheels can produce quite big torque i'm think it's quite low compare to lateral force that can generate 200N lateral forces.

I'm not saying what you said is wrong, it is perfectly right just like to have some time to compute gyro effect torque value on a standard motorbike to compare