What actually makes a bike turn?

[ronboskz650sr]

You just don't need the notion of 'centrifugal force' to explain how a bike turns.

Amen.

[Posthumane]

I agree with sv-wolf about "centrifugal force" not being a "real" force, but rather an imaginary force experienced by people due to their inertia resisting the centripetal acceleration caused by a turn. That's all I will say about that.

But, as to the earlier discussion about gyroscopic effects...
Yes, it is true that the spinning wheels in a bike have a gyroscope effect when in motion, and will help instigate a lean due to that effect. However, that force is very small when compared to the weight of the bike, so as to make it pretty close to negligible (or so I believe, as I haven't really tested this). Plus you have to remember that it is only the front tire that turns, and its leaning effect would be acting solely through the forks. I'm convinced that the horizontal displacement of the contact patch relative to the CG has a much greater effect on initiating a lean than the gyroscopic effects of wheels (hence, the bike on skis example works).

Another point is about the round section tires being responsible for turning a bike when leaned. Again, this may help a bit, but is not the primary cause for the turn. The main reason is simply that the front tire is allowed to turn (steer) relative to the rear. If the front wheel were locked to the frame and you leaned the bike, it would not turn but rather fall over. The ski example comes to mind again, as you can turn a bike on skis (or skates, or even a square section tire) despite the lack of round section tire causing a shorter distance traveled by the inside of the tire compared to the outside.

In conclusion, there are many different forces / effects that cause a bike to turn, some are just more pronounced than others.

And in response to the person who said people are "hard wired" to ride a bicycle, try telling that to a person who is trying to ride one for the first time... People just have a strong learning ability.

[sv-wolf]

You just don't need the notion of 'centrifugal force' to explain how a bike turns.

Amen.

Amen!

I might agree with that, after all last night's exertions, Ron. Though I have more trust in Newton's (real) physics than his (mythical) god.

[ZooTech]

Nice try, sv-wolf, trying to catch others off-guard with your lackluster use of big words and nit-picks over semantics. But the fact of the matter is, if centrifugal forces are not present and play no role in the leaning of a motorcycle, then why do scooters, with their much smaller diameter wheels, handle so much differently than regular motorcycles? How can you say it's not a "true" force simply because we are observing it from the outside looking in? The forks and swingarm of your bike are attached to the center of the wheels' hubs and therefore attempt to disrupt the forces in action on the spinning wheels any time the rider leans or steers. Everyone knows that a spinning wheel experiences gyroscopic forces (something you typically learn in oh, I dunno, like 8th grade science class) and attempting to turn the spinning front wheel one way or the other is met with resistance due to these forces in action. Because it's easier to deflect the steering head than it is to turn a spinning tire/wheel, the bike goes into a controlled fall in the opposite direction the bars were turned. And, while the centrifigal forces acting upon the wheels do not actually steer the bike, per se, you need them to initiate the lean needed to steer without simply falling over. Subsequently, you also need them to set the bike upright again after the turn.

Trying to confuse people and then pointing out when they misspeak is not a sign of intelligence...it's a sign of being a jackass.

[sv-wolf]

I agree with sv-wolf about "centrifugal force" not being a "real" force, but rather an imaginary force experienced by people due to their inertia resisting the centripetal acceleration caused by a turn. That's all I will say about that.

But, as to the earlier discussion about gyroscopic effects...
Yes, it is true that the spinning wheels in a bike have a gyroscope effect when in motion, and will help instigate a lean due to that effect. However, that force is very small when compared to the weight of the bike, so as to make it pretty close to negligible (or so I believe, as I haven't really tested this). Plus you have to remember that it is only the front tire that turns, and its leaning effect would be acting solely through the forks. I'm convinced that the horizontal displacement of the contact patch relative to the CG has a much greater effect on initiating a lean than the gyroscopic effects of wheels (hence, the bike on skis example works).

Another point is about the round section tires being responsible for turning a bike when leaned. Again, this may help a bit, but is not the primary cause for the turn. The main reason is simply that the front tire is allowed to turn (steer) relative to the rear. If the front wheel were locked to the frame and you leaned the bike, it would not turn but rather fall over. The ski example comes to mind again, as you can turn a bike on skis (or skates, or even a square section tire) despite the lack of round section tire causing a shorter distance traveled by the inside of the tire compared to the outside.

In conclusion, there are many different forces / effects that cause a bike to turn, some are just more pronounced than others.

And in response to the person who said people are "hard wired" to ride a bicycle, try telling that to a person who is trying to ride one for the first time... People just have a strong learning ability.

Posthumane, I agree with you about the gyroscopic effect being relatively small and therefore a very minor cause of lean on a bike. I wouldn't like to depend on it as the only means of getting me round a corner! I'd also agree with you that there are many forces that cause a bike to turn.

I would disagree though about the significance of the tyre profile. Yes, you can turn a bike on skis and I'll accept your assertion that you can turn it on a square tyre (though I have no knowledge of that and surely it would be very inefficient at speed - in the lean you would be squirrelling along on the tyre's edge). But I don't think this demonstrates anything about the turning forces involved on a conventional bike. A longitudinal ski introduces its own set of turning forces which are different from those of a round-profile tyred wheel. On a round profile tyre the differential traction between the faster spinning outside edge and the slower spinning inside edge would amount to a significant turning force - though not the only one.

You say that 'The main reason [a bike turns] is simply that the front tire is allowed to turn (steer) relative to the rear'. I'm not sure what you mean by 'steer'. I'm thinking here of a speedway bike, leaned right over in a corner with its front wheel pointing well away from its line of travel - an extreme form of counter steering. Of course there is some slide here, but I would strongly suspect speedway riders are using the differential forces in the tyre to get round.

Having said that, I've not investigated this at all - just playing round with the logic of what's being asserted. If you know of any research or analysis of these issues, I'd be glad to know where to find them.

[ronboskz650sr]

.... Though I have more trust in Newton's (real) physics than his (mythical) god.

None of anything you typed before this matters to me at all. This, however reveals alot more than the rest of it does. It even explains the need to refute..simply to refute. God is evident in nature to me, and your inclusion of him in this meaningless discussion doesn't matter any more than your refusal to believe in forces that are clearly felt, and are being used in everyday science...including the American space program. I am well aware of the differing opionions on centrifugal force, and have tried not to offend you...you haven't returned the courtesy. You need to step off the mathematical soapbox, and more fully research God before you die. The rest of this discussion won't matter to you at all then. There are no atheists in hell. Pm me if you need detailed information.

[sv-wolf]

Nice try, sv-wolf, trying to catch others off-guard with your lackluster use of big words and nit-picks over semantics. But the fact of the matter is, if centrifugal forces are not present and play no role in the leaning of a motorcycle, then why do scooters, with their much smaller diameter wheels, handle so much differently than regular motorcycles? How can you say it's not a "true" force simply because we are observing it from the outside looking in? The forks and swingarm of your bike are attached to the center of the wheels' hubs and therefore attempt to disrupt the forces in action on the spinning wheels any time the rider leans or steers. Everyone knows that a spinning wheel experiences gyroscopic forces (something you typically learn in oh, I dunno, like 8th grade science class) and attempting to turn the spinning front wheel one way or the other is met with resistance due to these forces in action. Because it's easier to deflect the steering head than it is to turn a spinning tire/wheel, the bike goes into a controlled fall in the opposite direction the bars were turned. And, while the centrifigal forces acting upon the wheels do not actually steer the bike, per se, you need them to initiate the lean needed to steer without simply falling over. Subsequently, you also need them to set the bike upright again after the turn.

Trying to confuse people and then pointing out when they misspeak is not a sign of intelligence...it's a sign of being a jackass.

Zoo. I do understand that you are trying to be rude, but I don't understand the point that you are trying to make about gyroscopic
forces. There are a number of forces which make a bike lean and another set that, once leaned, make it turn. The force exerted on the wheel hub by the forks results in a deflection of the wheel by 90 degrees ('gyroscopic progression') This has the effect of making the front wheel, and therefore the bike, lean. I think I said that in my first post. But it is a very small force and not sufficient to initiate a useful lean by itself. This has nothing to do with so-called centrifugal force.

I'm getting bored with going over and over this. The idea that there is something called centrifugal force which has some bearing on the way a bike or other rotating body moves in relation to its environment is a mistaken one and if you want to convince yourself of this go to your High Street book shop, buy a book on basic applied mathematics (mechanics), and look up rotational movement. This has been the understanding of mathematicians and engineers since the time of Isaac Newton in the seventeenth century.

As Ron pointed out, however, some engineers do use the term 'centrifugal force' in a limited sense to refer to a special situation that occurs within a rotating body. However, this is not the 'cenrifugal force' that is often mistakenly assumed to be responsible for making the body itself rotate in relation to its environment. What is required to make things rotate is a centripetal force which acts towards the centre of the turn - like the gravitational force acting on a moon that has been captured by a planet. The force Ron's engineers call centripetal force already has a perfectly good name in mathematical terminology - the normal force.

An example would be where a passenger in is apparently thrown against the side of a vehicle if it makes a sudden turn. What is actually happening though is that the passenger's inertia causes him to continue in his straight line motion while the side of the car whose line of motion has suddenly changed is swerving into him. When the turning car hits the passenger it exerts a force on him. The passenger then exerts and equal and opposite force on the door. This is usually called a 'normal force', but is what Ron's engineers have chosen to call a 'centrifugal force'. This is a real force - a 'true force' in Sev's terms. But it is not the force that has caused the turn. This normal force arises as a consequence of the turning force, which is the centripetal force acting on the car.

If you refocus away from what is going on inside the car and look at the car (in other words if you look at it from 'the outside') the only forces active upon it (as opposed to in it) are its weight acting through the centre of gravity, more normal forces acting vertically upwards through the contact patches of the wheels, and a frictional force (traction) acthing horizontally also at the wheels. People who think there is such a thing as centrfugal force assume this must be acting horizontally through the centre of gravity away from the turn. But mathematically and in reality it doesn't exist. Mathematically you can explain the entire motion of the vehicle in relation to its environment without it. If you try to include such a force the mathematics just falls apart. mechanical forces act by contact with one another. What is in contact with the bike at the centre of gravity to cause this? nothing.

By the way Zoo, your comment about my trying to catch people off guard is nonsense. I'm trying to explain what I learned about rotational force for three years as a student of mechanics. The sneering and sarcastic tone of your own post should make you less eager to throw insults around

[sv-wolf]

.... Though I have more trust in Newton's (real) physics than his (mythical) god.

None of anything you typed before this matters to me at all. This, however reveals alot more than the rest of it does. It even explains the need to refute..simply to refute. God is evident in nature to me, and your inclusion of him in this meaningless discussion doesn't matter any more than your refusal to believe in forces that are clearly felt, and are being used in everyday science...including the American space program. I am well aware of the differing opionions on centrifugal force, and have tried not to offend you...you haven't returned the courtesy. You need to step off the mathematical soapbox, and more fully research God before you die. The rest of this discussion won't matter to you at all then. There are no atheists in hell. Pm me if you need detailed information.

Thank you Ron. Rudeness is obviously the order of the day. My comment to you was meant humourously and not agressively as a statement of my belief and not a comment on yours. I have no beef with genuinely religious people, though I disagree with their doctrines, and how they interpret their religious experiences. So like Zoo I would say to you (as you stand on your religious soapbox lecturing to me about what I should do to amend my spiritual life and rather smugly informing me that you are in possession of an absolute truth and I am not) that you should consider your own personal motivations before making these rather spiteful remarks. I suspect from your remarks that you have little understanding of my personal views on these matters which are rather more complex than you assume.

I have no reason to dislike you Ron, but please understand that I view the world differently to you and do not accept your own assessment of yourself and your beliefs as having a central place in the scheme of things.

[ronboskz650sr]

I have no personal motivation...think about it. I have nothing to gain by your personal salvation. And, I'm not at all interested in winning an arguement. That's why I asked you to PM me for details if you want them. If you'd rather publicly stand against my absolute belief in the truth I believe, that's up to you...I was simply offering to you what I believe to be true, and I also believe you would benefit from it...not me. I won't respond publicly again, but I will publicly apologize for misinterpreting your statements...I obviously did, and I'm sorry.

[Sev]

As long as we're all up and getting annoyed I'm irritated that you never actually bothered to read what I had to say, and simply replied to catch phrases.

That being said I don't think this thread is going anywhere anymore. So lets all just agree that somewhere along the lines the rider makes the bike do something that makes it turn. And let the thread die before something we all regret is said.