BHS and countersteering

[Jantar]

Just move your shoulders slightly and tip your weight from one bum cheek to the other and note the bike tips gently into the corner. It's fine for humming along in a straight line and taking gentle bends, but a bar-push it is emphatically not, and for a sudden swerve it will do nothing.

It's all to do with how your ass gyroscopically progresses. I should start a wikipedia entry about it.

Steve

Please do. All this does is change the position of the center of gravity, it does not cause the bike to turn unless there is also a corresponding centripital force.

[Maki]

Just move your shoulders slightly and tip your weight from one bum cheek to the other and note the bike tips gently into the corner. It's fine for humming along in a straight line and taking gentle bends, but a bar-push it is emphatically not, and for a sudden swerve it will do nothing.

It's all to do with how your ass gyroscopically progresses. I should start a wikipedia entry about it.

Steve

Thanks for that, it had me wondering. If anyone has any doubts about the effectiveness of ass steering, try steering with no hands. Yes, just take your hands off the bars and see what happens if you lean this way or that way. The bike will turn gently...

I agree that countersteering is a more powerful way to steer your bike and you need to do it to change direction suddenly.

[marty]

If we have any resident helichopter pilots they will be able to expand more, the main rotor disk suffers a lot of precession effects.

they don't 'suffer' from it - it's just the way it is. in fact they have to account for it in all inputs to the main rotor head.

the early rotary engined aircraft (sopwith camel for eg) DID 'suffer' from presession - so much in fact that at high RPM, the forces due to precession from the rotating engine was higher than the aerodynamic forces, and the only way to turn the aircraft was to pull or push on the stick. killed a lot of pilots. rudder or aileron input would cause it to climb or descend. took a bit to figure out what was happening....

now imagine if one piece of the rotating mass was fixed to the ground - (the tyre contacting the road) how much force would there be at the top of the wheel?

[Jantar]

Thanks for that, it had me wondering. If anyone has any doubts about the effectiveness of ass steering, try steering with no hands. Yes, just take your hands off the bars and see what happens if you lean this way or that way. The bike will turn gently.......

"Gently" being the operative word. What is happing is that all you done is shift the bike's CoG. The bike appears to take on a bit of a lean, but your body is compensating, so the the CoG is still upright. However there are two other effects that come into play: Because the tyres (particularly the front) are not square, there is a slight conical effect which means part of the contact patch of the tyre has a slightly different rolloing radius to the part closest to the center of the tyre. Hence the bike will gently change direction.

The slight lean taken on by the wheel will cause a gyroscopic precession, in the opposite direction to that which is desired. This causes the front wheel to move off line slightly (also part of the counter steering effect) and the corresponding shift in balance will also tend to turn the bike gently.

Now try hands off and shift your arse at low speed, say 20 kmh, and see how long before you hit the ground. There is not enough speed for precession to work, and you will be likely to come off.

[paddy]

they don't 'suffer' from it - it's just the way it is. in fact they have to account for it in all inputs to the main rotor head.

Bad choice of word on my part - I was just trying to indicate that precession was a significant element in all elements of helicopter flight operations.

(Having said that, as a fixed wing pilot, I could possibly hold the opinion that helicopters "suffer" from all sorts of issues. Lets start with way too many moving parts...) :-)

[Maki]

Now try hands off and shift your arse at low speed, say 20 kmh, and see how long before you hit the ground. There is not enough speed for precession to work, and you will be likely to come off.

http://www.break.com/usercontent/200...sh-526486.html

[Jantar]

http://www.break.com/usercontent/200...sh-526486.html

I went to your link, but its a video. I'm on dial up so I've no idea what its about or what point you are trying to make.

[paddy]

http://www.break.com/usercontent/200...sh-526486.html

The problem with links like this is that they are addictive - I moved on from the R6 crash to "How not to scale columns" to "Painful leap of faith over river" to "Emo kid can't breath after fall" to "Angry Roady Tries to Fight Band Onstage" (I love how the guitarist keeps going in that one) to. . .

Ahhh...I can't seem to stop. :-)

[Maki]

I went to your link, but its a video. I'm on dial up so I've no idea what its about or what point you are trying to make.

No problem. It shows a guy riding with no hands at a slow speed and dropping the bike.

You wrote: "Now try hands off and shift your arse at low speed, say 20 kmh, and see how long before you hit the ground." The video shows exactly that happening...

[Jantar]

Thanks for that. I'm always amazed at the number of people wh think they can defy the laws of physics.

[Sheba]

Thanks for those who included the videos. I found them very helpful. It also gets me itching to try that someday and get on a bike soon....after a BHS course, of course.

[Markw336]

dont worry the instructor tells you how to do these sorts of thing i found it easy it would be quite hard to fail

[R-Soul]

It is actually - sorry I couldn't resist. You should stop reading now if you are easily bored. :-)

It's caused by an effect called gyroscopic precession. Basically, any force applied to a rotating body will be "precessed 90 degrees in the direction of rotation". So, if you had a spinning disk with the flat side facing you, and it was rotating clockwise, then you pushed the top of the wheel away from you, you would actually expect the top of the disk to stay reasonbly in place, but the right hand side of the disk would move away from you. That is to say, the force that you apply would appear as if you had applied it 90 degrees away in the direction of rotation.

So, if we apply that to handlebars, turning the bars to the right you are moving the front of the wheel to the right and the rear of the wheel to the left. These forces are precessed 90 degrees in the direction of rotation. That means that (assuming you are riding forwards) the top of the wheel is going to try and move to the left, and the bottom of the wheel is going to try and move to the right (although in reality this is prevented by friction with the road surface and therefore just has a levering effect adding more force to the displacement at the top of the wheel).

The wheel isn't spinning fast enough for the forces of gyroscopic precession to overcome the weight/momentum of the bike until you are moving at around 15 - 20 KM/H.

It used to be fun when we where kids to take our push-bike wheel off. Hold them on both sides by the axle and have someone spin the wheel by hand. You could then tip the wheel in various directions and feel the precession (not that I knew it's name or nature back then).

If we have any resident helichopter pilots they will be able to expand more, the main rotor disk suffers a lot of precession effects.

There. Got that off my chest.

I never really thought about countersteering that way. I always just thought that what you are doing is steering the bike out from under your weight. When the bike is off to the side, leaning towards you, and your weight is pushing it further over, then this counterbalances the forces acting on you in a corner, keeping you upright. But I guess teh gyroscopic explanation helps explain why it does not work as well at low speeds.

And regardless of what anyone says about small bikes, the concept is just as useful and relevant, and gives you a HELL of a lot more control of your bike. Trying to control a 150kg bike with a 60-90 kg bodyweight is dificult at best. The day I figured it out was teh first day I felt I had true control of my bike.

SO: If you want to go left, push FORWARD (slightly) on the left bar, and vice versa.
But this only really applies to speed 20km/h and over.

[R-Soul]

Countersteering is not for everybody, Arron Slight does not beleive there is such a thing. Its such a slight (scuse the pun) pushing movement, more of a 'weighting the bar' really, you hardly even notice you're doing it, just lean and go around the corner, the bike will do that.

I started consciously pushing on the bar, but at speed I like pushing my shoulders and weight to to the inside while keeping my arms straight. This automatically pushes the inside bar away frm me, and induces counter steer.

When you have it ingrained, you can actually move your body weight to the outside while countersteering, and make the bike lean over further (to scrub off the sissy strip). when you use this technique, you realise how little effect or control your body weight actually has on the bike's movement.

[proseuche]

Drove Akld-New Plymouth-Akld this weekend, very fun ride. My first open road ride too, tackled Mt Messenger and Awakino Gorge no probs (then nearly got crashed into in Remuera, 2 blocks from home, *(&@#*@).

Anyway, about mid-way through the return trip I realised it was easier and quicker to take the corner by looking into it and sort of swivelling your hips so the bike moves over and leans, while keeping your upper body sort of in the same position. Anyway, i wondered whether I was teaching myself a bad habit, but seems not.. thanks for the info :]