Countersteering Confession

[marty]

Watch what happens at that strange sport called bowls. The bowler can get the bowl to turn in without counter sterring because of two seperate effects. First there is a weight bias which causes the bowl to want to lean in the direction of the turn, (like leaning a bike) then there is the shape of the bowl which causes the surface to have a different profile as it leans more (like your paper cup). Counter steering helps with the weight transfer, and tyre geometry helps with the right profile.

exactly - the bowl turns toward the centre of gravity. the bowl wants to go straight ahead, and it will if the speed of the bowl is high enough, but the c of g forces at lower speed will tend to turn the bowl towards that force. the same if you lean your bike without touching the bars - the bike's c of g acts straight down, but now instead of acting through the wheels, it acts vertically down to a point inside the turn, and the bike turns towards it.

[marty]

Read about it here...

thanks.......

[rwh]

The wheels move out from under the bike to the side while the centre of gravity of the bike stays put, hence the bike topples and I turn. I tested that out last year when I first joined this site. But I'll report on the bmx wheel test tomorrow...

Agreed. I tried out the bike wheel this afternoon (bike already conveniently in bits), and was quite surprised how strong the precession was - but I'm not convinced it could do the whole job. Especially since I'm sure countersteering would still work fine on one of those little pushalong scooters with 10cm wheels; those wheels won't have enough mass to tip me over.

I'm not saying the gyroscopic effect has nothing to do with it; I'm just not convinced it's the whole deal.

Essentially - I think I agree with erik. I was going to try to explain it, but he did so much better with his balancing broomstick.

Richard

[Jamezo]

Yeesh guys, I thought that this had been cleared up many times before.

The precession force acts in OPPOSITION to the change in angle of the bike.

The input to the bars changes the position of the contact surface of the wheel in relation to the movement of the bike, and sets up the rotational force.

The turning itself is a direct consequence of the angle of the bike.

[Mr. Peanut]

Wen ai tern tha handul baas tha boike gows otherwheres

EDIT :

E=mc^2

[marty]

Agreed. I tried out the bike wheel this afternoon (bike already conveniently in bits), and was quite surprised how strong the precession was - but I'm not convinced it could do the whole job. Especially since I'm sure countersteering would still work fine on one of those little pushalong scooters with 10cm wheels; those wheels won't have enough mass to tip me over.


Richard

the fastest you could get you bmx wheel up to by spinning would be 10kmh. times that by 10, then tell me the force wouldn't be enough

[marty]

and i respectfully suggest your broomstick comparison is irrelevant, as the experiment, if done on a stationary bike (eg pull on the right bar) will not invoke a precessed response. the gyro (the wheel) is what makes the difference. if it is not spinning, it is not a gyro.

do some reading on fixed gyros. the front wheel of a bike is a horizontal fixed gyro

[Motig]

Sorry, I should have put this topic in the 'Scientific Anylasis' Forum.

[terbang]

When we drive around a carpark at 10 kays or less we can drive the thing like a car. Same as when you are pushing it around yer garage. Turn bars right, bike turns right. We all know that don't we..? We also all know (with out really thinking about it) that as we get faster we can't steer it like a car anymore and have to lean the thing to make it turn. So whats the difference between the slow and the not so slow..? Its gyroscopic force along with its precession properties. Simple really.

[terbang]

Counter steering does not so much turns the bike around the corner.
It makes the bike lean over in to the corner so you can go around it.
It is used more to start the turn and finish a turn.
You only use it to change the (lean) angle of the bike.

I think that you use the gyroscopic effect of the front wheel to push against (a bit like a wall or a lever) to push the bike down in to a corner or to get the bike back up to vertical.

Other wise when you have your knee down, it would be impossible to counterbalance the bike up right again as you are way passed the point of balance.
That is unless you can lean your body passed the vertical point to get the bike to stand up again. (I would like to see that)

When you just lean a bike in to a corner (with out hands off the bars) the wheel turns the the way you want to go, but you will not be leaning the bike over as much, but will still go around the corner, but not as fast.
Because if you go passed the point of no return you will not be-able to straighten up the bike again.

Bingo.. Countersteer doesn't turn the bike it only controls the bike in a lateral sense. In simple words it is the roll control and we lean the bike and mnaintain a lean angle with it. The turning force (centre seeking force) is now provided by the tyre which is in effect a segment of a cone (someone mentioned a paper cup before).

[marty]

Sorry, I should have put this topic in the 'Scientific Anylasis' Forum.

at least the sun's shining where i am

[erik]

The broomstick example is supposed to demonstrate that when you try to accelerate the broom in one direction, it has to be leaned in that direction first otherwise it'll topple over.
When you ride a bike around a corner, it is accelerating towards the centre of the curve (centripetal acceleration). To avoid from toppling over (out of the corner), it has to be leaned into the curve.

The broomstick example also demonstrates that to get the broom to lean in one direction, you have to move the base briefly in the opposite direction.
Ignoring gyroscopic effects on a bike, turning the front wheel to the right would make the contact patch of the front tyre track to the right (if the bike is moving forwards) and the bike would start to lean towards the left, ready to turn in that direction.

This still holds true at low speed, if you turn hard to the right, the bike will tip to the left (depending on how much trail the bike has and how hard you turn...). You still have to balance the bike.

I know how a gyroscope works (I've got a toy one sitting on my desk). I'm not saying gyroscopic precession doesn't play a part in a bikes handling. At high speed for all I know it might be the main force that controls how the bike leans. It might come into effect before the front wheel has a chance to track to the side.
But it's confusing for me that you can't see that when you turn the bars to the right, the wheel will track to the right under the bike, and the bike will lean left.
I intend to do some reading over summer to get a better grasp of motorcycle dynamics.

Appologies for hijacking your thread, Motig

[Motig]

Not a problem. Suns shining here too!

[terbang]

turning the front wheel to the right would make the contact patch of the front tyre track to the right (if the bike is moving forwards) and the bike would start to lean towards the left, ready to turn in that direction.

Turn the bars right and the tyre contact point, due to the trail, shifts to left of the bikes centreline.

[marty]

But it's confusing for me that you can't see that when you turn the bars to the right, the wheel will track to the right under the bike, and the bike will lean left.

this is not what happens erik. when you pull on the right bar while the wheel is rotating at speed, the input that you have done, due to GP, effectively 'pushes' the top of the front wheel over to the left. the bottom of the tyre is 'fixed' to the road, so the point of rotation of the gyro (the wheel), instead of rotating about its axis, is about that 'fixed' point on the road. the wheel does not track to the right at all, otherwise the bike would initially turn/drift to the right.

i've got some really good books on gyro theory - essential reading for helo engineers, and general aircraft engineers (which is what i do)