The Bum Steer

[jrandom]

I found the opposite, the bars tend to tip in. This is on a 50km/h downhill gentle curve using body weight shift alone, hands off bars.

You know... come to think of it, you're quite right.

I hadn't really thought about what the bars did during hands-off steering until now, and got my visualisation round the wrong way.

[MSTRS:Me]

...what initiates the actual turn is the displacement of the front wheel contact patch.....

The crux of the whole discussion. Something you do that causes the contact patch of the front tyre to move off-centre. Assuming the steering head is free to move, the bike will lean and turn in the direction that patch 'moved'.
But still, to move that contact patch quickly and concisely requires input through the bars...
And Deano/Jrandom...there will be a momentary turn of the bars in the opposite direction to the turn, before they turn in line with the direction of that turn.

[jrandom]

You're perpetuating the myth that counter steering is pointless, or at best conditional, with your attitude, which means I can't respect that opinion at all.

Surely nobody of sound mind could interpret my comments to mean that countersteering is either pointless or conditional. Pushing on the bars into a corner is obviously the correct way to steer a motorcycle, and in fact the only way when one is doing anything other than pissing about at low speed.

I get vastly more fun from dialling up the correct angle of lean for a given speed and corner radius so I don't have to correct, or I can precisely modify a line, than I ever would from taking my hands of the bars...

You should try the canoe-paddling trick sometime when you have a pedestrian audience.

[Ocean1]

I can steer a bike around corners as it rolls in gear downhill doing 50-60kph with my hands off the bars, using my hips and knees and waving my upper body about,

It depends on the amount of mass required

and10stuff

[jrandom]

Like I keep saying. They're racing pies.

[Ocean1]

You did indeed not read my post I see.

My argument was that the guy who made an attempt at counter-rotating weights to cancel out the gyroscopic effect of the wheels didn't do it properly...

If he had, he would indeed not have been able to ride the bike in a straight line (or most likely not at all)... As such, the conclusions derived from his study of the behaviour of such a bike would be without merit.

It has nothing to do with speed or how the bike reacts to steering input - simply the fact that if you completely eliminate the gyroscopic effect of the bike it's not going to be rideable (at any speed).

And the pushbikes with skis instead of wheels wot you see kids playing on the slopes?

[mowgli]

That's a little different - the steering is accomplished by a controlled fall (and recovery) in the direction you're steering in. You're moving the C of G towards the intended direction of travel.

Not quite. A fall alone won't do it.

The change of direction is caused by the unbalanced side force acting on the tyres. This is caused by a combination of gravity pulling the bike over and momentum pulling it upright. Lean angle and speed are the variables that determine the magnitude of the unbalanced force and therefore the rate of turn.

Edit: road camber will also add/subtract to the side force created.

But for most of us we think I wanna go left and the bike goes left.

[Ocean1]

Like I keep saying. They're racing pies.

And cake, don't fergit the cake.

I haven't.

Bastard.

[MSTRS:Me]

Not quite. A fall alone won't do it.

The change of direction is caused by the unbalanced side force acting on the tyres. This is caused by a combination of gravity pulling the bike over and momentum pulling it upright. Lean angle and speed are the variables that determine the magnitude of the unbalanced force and therefore the rate of turn.

But for most of us we think I wanna go left and the bike goes left.

Aggghhhh...there's that word 'thinking' again!!

[jrandom]

This is caused by a combination of gravity pulling the bike over and momentum pulling it upright. Lean angle and speed are the variables that determine the magnitude of the unbalanced force...

You utter muppet; all you did there was rephrase vifferman's post.

[jrandom]

Aggghhhh...there's that word 'thinking' again!!

Cogito ergo inclino?

[Ixion]

The crux of the whole discussion. Something you do that causes the contact patch of the front tyre to move off-centre. Assuming the steering head is free to move, the bike will lean and turn in the direction that patch 'moved'.
But still, to move that contact patch quickly and concisely requires input through the bars...
And Deano/Jrandom...there will be a momentary turn of the bars in the opposite direction to the turn, before they turn in line with the direction of that turn.

Yes. You can move it whatever way, but USUALLY the best way , and the most controllable, is to move the handlebars. That , after all, is what they are there for. And since discussions about how to steer a motorcycle usually are focused on beginners (if you've been riding for years, presumably you've found out how to go round corners, one way or another. Or have a VERY long driveway). And it's a good ideea to give them the simplest safest most reliable method.

And the reason , ultimately, that moving the front wheel contact patch causes you to go in an arc, is that the front wheel is trying to catch up with the rear wheel , since both are attempting to follow the path of the centre of mass, but can't because of the frame holding them apart .

[Mikkel]

You should read the article I just linked on trail.

Motorcycle stability comes from trail, not from gyroscopic effects.

With all due respect. That is a load of rubbish. I'm not going to say that the trail doesn't play a role in stability - because it does. But the actual balance that keep your bike upright while you're riding stems from the rotational mass!
The trail is what determins how easily that balance is upset - easily upset means sharp turn-in and high maneouverability but a bit jerky and unsettled for cruising...


Now, I apologise for my poor paint skills but..., here's a sketch of the force vectors in a leaned over motorcycle. Fn is the normal force proviceded by the tyres (it goes from the contact patches through the centre of mass!), Fg is the gravitational forces working on the centre of mass (COM - the blue spot) and F1 and F2 are composants of the normal force. F1 will have the same magnitude as Fg - otherwise the bike either starts sinking into the tarmac or starts levitating. The lean angle then quite simply dictates how big you make F2 - or how much cornering force you have available. Now, if you shift your COM of the axis of the bike by shifting your weight off the saddle it is easy to see how you can get the normal force vector on a higher degree of lean while keeping the bike upright.
This is the basic force balance. All the frustrating details such as steering geometry and such you can leave out...

[007XX]

And cake, don't fergit the cake.

I haven't.

Bastard.

Oh FFS...would you just let it go?!?

Aggghhhh...there's that word 'thinking' again!!

Just strained a braincell there, did ya?

What I don't understand (and of course, cos I'm just a poor little bird brain female, yaddi yadda...blah, blah) is why you guys keep on arguing about something you all fundamentally seem to agree on in principal?

Secondly, how is you brainiacs flinging scientific terms at each other going to help your average, 100 IQ, and probably still needing training wheels Newbie...And yes, I mean me mostly

So speak in goddarn lemens terms please...

Ok, I'll go and have a cup of tea and a lie down now...

[Forest]

With all due respect. That is a load of rubbish. I'm not going to say that the trail doesn't play a role in stability - because it does. But the actual balance that keep your bike upright while you're riding stems from the rotational mass!
The trail is what determins how easily that balance is upset - easily upset means sharp turn-in and high maneouverability but a bit jerky and unsettled for cruising...

No it doesn't. The bikes with counter-rotating weights show this isn't true.

Stability derives from trail. If you don't accept this, try riding a bike with no trail and report back to us on the high speed stability.

Now, I apologise for my poor paint skills but..., here's a sketch of the force vectors in a leaned over motorcycle. Fn is the normal force proviceded by the tyres (it goes from the contact patches through the centre of mass!), Fg is the gravitational forces working on the centre of mass (COM - the blue spot) and F1 and F2 are composants of the normal force. F1 will have the same magnitude as Fg - otherwise the bike either starts sinking into the tarmac or starts levitating. The lean angle then quite simply dictates how big you make F2 - or how much cornering force you have available. Now, if you shift your COM of the axis of the bike by shifting your weight off the saddle it is easy to see how you can get the normal force vector on a higher degree of lean while keeping the bike upright.
This is the basic force balance. All the frustrating details such as steering geometry and such you can leave out...

Notice how there are no vectors for gyroscopic forces in your diagram?

Funny that.