The Naked Scientists

The Naked Scientists Forum

Author Topic: falling off my bike  (Read 13326 times)

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
falling off my bike
« on: 16/09/2006 19:57:16 »
Why is it easier to stay on a bike while moving?

What you do speaks so loudly that I cannot hear what you say.


 

Offline Simmer

  • Sr. Member
  • ****
  • Posts: 229
    • View Profile
Re: falling off my bike
« Reply #1 on: 16/09/2006 20:29:14 »
Momentum!
 

another_someone

  • Guest
Re: falling off my bike
« Reply #2 on: 16/09/2006 20:44:39 »
Actually, I think one important aspect is the gyroscopic effects of the wheels (which is why it is easier to stay on a large wheeled bike than a small wheeled bike).  Probably linear momentum also plays some part, but in most cases I think the gyroscopic effect is probably the more significant.



George
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #3 on: 17/09/2006 03:45:32 »
100 % gyroscopic effect.

By the way: if you are riding byke at no very low speed (~ > 30Km/h) and you want to turn left, wich direction you have to turn the handle bar, left or right?

In case you answer "left", you're wrong, it's the opposite (gyroscopic effect).
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #4 on: 17/09/2006 11:28:37 »
I think that the gyroscopic effect in bicycle riding is highly overrated here !  Bicycle wheels are very light when compared to the total weight of bike + rider.  And if the gyroscopic effect is as important as you state here, then the old penny-farthing bicycles (with the high frontwheel and the small rear wheel) would be more stable than the modern bikes.  I can assure you this in NOT the case.
The effect of turning to the right when you turn your handlebars to the left is related to geometry of the bicycle.  The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.  (That is also the way you steer when you take your hands off the handlebars.)  
This is not only true at low speeds (I would not call 30 km/h a low speed for a bicycle rider anyway).  Just watch speedway races or the American dirttrack races for motorbikes.
The main reason why it is easier to stay upright on a moving bicycle is that it is much easier to make corrections while moving.  And if you want to estimate how many corrections you make when riding a bicycle, just make a stretch over wet sand (e.g. on the beach, just after high tide), and observe the tracks of the front and rear wheels.  Remember the front wheel is the one you make the corrections with.
This is also the reason why it is so difficult for novices to ride on the old three roller type of home trainers when the bicycle is not fixed by some means.
The physiscs of cycling is realy a subject to expand on !
« Last Edit: 17/09/2006 11:30:07 by eric l »
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Re: falling off my bike
« Reply #5 on: 18/09/2006 13:52:10 »
The stability of a moving bycycle is a classic negative feedback effect.  It is caused by first being able to steer as you move to correct any tendancy to fall over in one direction or the other by steering into the direction of fall and thus correcting it and secondly by having the turning axis of the front weheel angled and offset from rotation axis which causes the handlebars to be stable and tend to centre itslf and automatically steer into the direction that the bike is falling.  That is why it is possible to ride a bycycle without holding on to the handlebars it will for small corrections steer itself.  If you dont believe this second effect is important is important try riding a bike with the front wheel turned through 180 degrees so this effect is in the opposite direction.  The bike becomes almost unridable

Learn, create, test and tell
evolution rules in all things
God says so!
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #6 on: 18/09/2006 14:37:36 »
quote:
Originally posted by eric l

I think that the gyroscopic effect in bicycle riding is highly overrated here !  Bicycle wheels are very light when compared to the total weight of bike + rider.  And if the gyroscopic effect is as important as you state here, then the old penny-farthing bicycles (with the high frontwheel and the small rear wheel) would be more stable than the modern bikes.  I can assure you this in NOT the case.
The effect of turning to the right when you turn your handlebars to the left is related to geometry of the bicycle.  The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.  (That is also the way you steer when you take your hands off the handlebars.)  
This is not only true at low speeds (I would not call 30 km/h a low speed for a bicycle rider anyway).  Just watch speedway races or the American dirttrack races for motorbikes.
The main reason why it is easier to stay upright on a moving bicycle is that it is much easier to make corrections while moving.  And if you want to estimate how many corrections you make when riding a bicycle, just make a stretch over wet sand (e.g. on the beach, just after high tide), and observe the tracks of the front and rear wheels.  Remember the front wheel is the one you make the corrections with.
"Bike" means "bicycle" or "motorbike"? I thought the question was related to "motorbike".
quote:
The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.
If you turn your handlebar to the left, the frame of the bike (and your body) will be inclined to the right, just because of gyroscopic effects: applying a force momentum to the axe of a spinning wheel, makes it to precede, as gravity on a spinning top on a table.

« Last Edit: 18/09/2006 14:38:29 by lightarrow »
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: falling off my bike
« Reply #7 on: 18/09/2006 14:40:08 »
One of the big moments on a bike is getting your knee on the ground in a corner. It takes a big leap of faith to do it the first time. Your whole head is saying impossible you are going to die. The first time it happen to me I had no choice I had  came in to hot and just had to go over on to the side of my tyre or I was going to run out of road.. I could not believe how hard it was to pull it down. I was literally hanging off it.

What you do speaks so loudly that I cannot hear what you say.
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #8 on: 18/09/2006 15:56:27 »
With a motorbike you have more gyroscopic effect from the flywheel of the engine and the rotor of the alternator than from the wheels.  That's why riding a bike with the crankshaft in line with the driveshaft (like a BMW-boxer or a MotoGuzi) feels so different.  I think Honda solved the problem with the Goldwing by making the alternator turn in the opposite direction to the crankshaft.
And your frame will tilt to the right if you turn your handlebars to the left even at standstill, when there is no question of gyroscopic effect.
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: falling off my bike
« Reply #9 on: 18/09/2006 16:07:37 »
Yea I agree except I not certain if you can count a tank like the Goldwing as a true bike it so big and heavy I say it can stand by itself for an hour or two before it would know you had got off it. :D

What you do speaks so loudly that I cannot hear what you say.
 

Offline Simmer

  • Sr. Member
  • ****
  • Posts: 229
    • View Profile
Re: falling off my bike
« Reply #10 on: 16/09/2006 20:29:14 »
Momentum!
 

another_someone

  • Guest
Re: falling off my bike
« Reply #11 on: 16/09/2006 20:44:39 »
Actually, I think one important aspect is the gyroscopic effects of the wheels (which is why it is easier to stay on a large wheeled bike than a small wheeled bike).  Probably linear momentum also plays some part, but in most cases I think the gyroscopic effect is probably the more significant.



George
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #12 on: 17/09/2006 03:45:32 »
100 % gyroscopic effect.

By the way: if you are riding byke at no very low speed (~ > 30Km/h) and you want to turn left, wich direction you have to turn the handle bar, left or right?

In case you answer "left", you're wrong, it's the opposite (gyroscopic effect).
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #13 on: 17/09/2006 11:28:37 »
I think that the gyroscopic effect in bicycle riding is highly overrated here !  Bicycle wheels are very light when compared to the total weight of bike + rider.  And if the gyroscopic effect is as important as you state here, then the old penny-farthing bicycles (with the high frontwheel and the small rear wheel) would be more stable than the modern bikes.  I can assure you this in NOT the case.
The effect of turning to the right when you turn your handlebars to the left is related to geometry of the bicycle.  The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.  (That is also the way you steer when you take your hands off the handlebars.)  
This is not only true at low speeds (I would not call 30 km/h a low speed for a bicycle rider anyway).  Just watch speedway races or the American dirttrack races for motorbikes.
The main reason why it is easier to stay upright on a moving bicycle is that it is much easier to make corrections while moving.  And if you want to estimate how many corrections you make when riding a bicycle, just make a stretch over wet sand (e.g. on the beach, just after high tide), and observe the tracks of the front and rear wheels.  Remember the front wheel is the one you make the corrections with.
This is also the reason why it is so difficult for novices to ride on the old three roller type of home trainers when the bicycle is not fixed by some means.
The physiscs of cycling is realy a subject to expand on !
« Last Edit: 17/09/2006 11:30:07 by eric l »
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Re: falling off my bike
« Reply #14 on: 18/09/2006 13:52:10 »
The stability of a moving bycycle is a classic negative feedback effect.  It is caused by first being able to steer as you move to correct any tendancy to fall over in one direction or the other by steering into the direction of fall and thus correcting it and secondly by having the turning axis of the front weheel angled and offset from rotation axis which causes the handlebars to be stable and tend to centre itslf and automatically steer into the direction that the bike is falling.  That is why it is possible to ride a bycycle without holding on to the handlebars it will for small corrections steer itself.  If you dont believe this second effect is important is important try riding a bike with the front wheel turned through 180 degrees so this effect is in the opposite direction.  The bike becomes almost unridable

Learn, create, test and tell
evolution rules in all things
God says so!
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #15 on: 18/09/2006 14:37:36 »
quote:
Originally posted by eric l

I think that the gyroscopic effect in bicycle riding is highly overrated here !  Bicycle wheels are very light when compared to the total weight of bike + rider.  And if the gyroscopic effect is as important as you state here, then the old penny-farthing bicycles (with the high frontwheel and the small rear wheel) would be more stable than the modern bikes.  I can assure you this in NOT the case.
The effect of turning to the right when you turn your handlebars to the left is related to geometry of the bicycle.  The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.  (That is also the way you steer when you take your hands off the handlebars.)  
This is not only true at low speeds (I would not call 30 km/h a low speed for a bicycle rider anyway).  Just watch speedway races or the American dirttrack races for motorbikes.
The main reason why it is easier to stay upright on a moving bicycle is that it is much easier to make corrections while moving.  And if you want to estimate how many corrections you make when riding a bicycle, just make a stretch over wet sand (e.g. on the beach, just after high tide), and observe the tracks of the front and rear wheels.  Remember the front wheel is the one you make the corrections with.
"Bike" means "bicycle" or "motorbike"? I thought the question was related to "motorbike".
quote:
The line from the axle of your front (=steering) wheel to the steering head is not vertical, so if you turn your handlebar to the left, the frame of the bicycle (and your body) wil be inclined to the right.  Inclining to the right will make you turn right.
If you turn your handlebar to the left, the frame of the bike (and your body) will be inclined to the right, just because of gyroscopic effects: applying a force momentum to the axe of a spinning wheel, makes it to precede, as gravity on a spinning top on a table.

« Last Edit: 18/09/2006 14:38:29 by lightarrow »
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: falling off my bike
« Reply #16 on: 18/09/2006 14:40:08 »
One of the big moments on a bike is getting your knee on the ground in a corner. It takes a big leap of faith to do it the first time. Your whole head is saying impossible you are going to die. The first time it happen to me I had no choice I had  came in to hot and just had to go over on to the side of my tyre or I was going to run out of road.. I could not believe how hard it was to pull it down. I was literally hanging off it.

What you do speaks so loudly that I cannot hear what you say.
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #17 on: 18/09/2006 15:56:27 »
With a motorbike you have more gyroscopic effect from the flywheel of the engine and the rotor of the alternator than from the wheels.  That's why riding a bike with the crankshaft in line with the driveshaft (like a BMW-boxer or a MotoGuzi) feels so different.  I think Honda solved the problem with the Goldwing by making the alternator turn in the opposite direction to the crankshaft.
And your frame will tilt to the right if you turn your handlebars to the left even at standstill, when there is no question of gyroscopic effect.
 

Offline Hadrian

  • Neilep Level Member
  • ******
  • Posts: 2175
  • Scallywag
    • View Profile
Re: falling off my bike
« Reply #18 on: 18/09/2006 16:07:37 »
Yea I agree except I not certain if you can count a tank like the Goldwing as a true bike it so big and heavy I say it can stand by itself for an hour or two before it would know you had got off it. :D

What you do speaks so loudly that I cannot hear what you say.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #19 on: 18/09/2006 20:40:46 »
quote:
Originally posted by eric l

With a motorbike you have more gyroscopic effect from the flywheel of the engine and the rotor of the alternator than from the wheels.
I don't agree. Certainly a flywheel's angular speed is much greater than a wheel's angular speed, but a wheel's moment of inertia is also much greater than that of a flywheel, not only because of the greater mass M but, mostly, because of the greater radius R: I = a*M*R^2 where a depends on the form (a = 1 for a ring, = 1/2 for a disk). Gyroscopic effects depend on angular momentum K, which depends on angular speed w and on I: K = I*w.
quote:
And your frame will tilt to the right if you turn your handlebars to the left even at standstill, when there is no question of gyroscopic effect.
At standstill, whatever you do, you will fall to the ground with a heavy moto, if it tilts more than a certain angle, but you don't fall, even at an higher angle, if you go over a certain speed (~ 30 Km/h with my Yamaha FZ750) and the greater the speed, the more difficult it is to tilt the moto. A moto (or a bicycle) running without any rider can keep going straight, until its speed lowers under the value at wich gyroscopic effects becomes less important.
« Last Edit: 18/09/2006 20:58:16 by lightarrow »
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #20 on: 19/09/2006 08:52:01 »
OK, so you are going through a turn with your TZ750 at 30 km/h, at an angle at which you would fall if you and the motorcycle would stand still.  But that is simply because turning at that angle you are in equilibrium !  In fact, if you would stay vertical (I do not use the word upright on purpose) cornering at that speed, you would fall off, but on the other side.
Watch a car going through a corner at even a moderate speed.  You can not lean it over like you lean over a bicycle or motorcycle.  And what will you see ?  Due to inertia - which in this case will be called "centrifugal force" - the car will be pushed to the outside, and the suspension will allow it to be tilted outwards (unless the car has a really sophisticated computer controlled suspension).  The stiffer suspension of a sports car will allow it to corner faster before tilting over.
Cornering on a motorcycle, you lean over to the inside, so that the resultant of centrifugal force and gravity pass through the line between the contact patches where your front and rear wheels touch the road.
And the importance of the gyroscopic effect of the engine is demonstrated in trials (I mean the sport), where the rider revs up the engine while letting the clutch slip so that he (or she) can profit from the gyroscopic effect without the wheels turning.
« Last Edit: 19/09/2006 08:59:29 by eric l »
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #21 on: 19/09/2006 11:55:50 »
quote:
Originally posted by eric l

OK, so you are going through a turn with your TZ750 at 30 km/h, at an angle at which you would fall if you and the motorcycle would stand still.  But that is simply because turning at that angle you are in equilibrium !  In fact, if you would stay vertical (I do not use the word upright on purpose) cornering at that speed, you would fall off, but on the other side.
Watch a car going through a corner at even a moderate speed.  You can not lean it over like you lean over a bicycle or motorcycle.  And what will you see ?  Due to inertia - which in this case will be called "centrifugal force" - the car will be pushed to the outside, and the suspension will allow it to be tilted outwards (unless the car has a really sophisticated computer controlled suspension).  The stiffer suspension of a sports car will allow it to corner faster before tilting over.
Cornering on a motorcycle, you lean over to the inside, so that the resultant of centrifugal force and gravity pass through the line between the contact patches where your front and rear wheels touch the road.
And the importance of the gyroscopic effect of the engine is demonstrated in trials (I mean the sport), where the rider revs up the engine while letting the clutch slip so that he (or she) can profit from the gyroscopic effect without the wheels turning.

I have no doubt there is centrifugal force and gravity in opposite directions, in a bend, and I have no doubt about the existence of engine's gyroscopic effect, especially in trial motorbikes, where the flywheel is big and heavy on purpose, to have a big torque at low rev.

But you can be aware of gyroscopic effect even on a straight road: you make a slight force on your handlebars to make them turn left, and the moto tilts to the right, and this effect increases with the moto's speed. You say this is because of gyroscopic effect from the engine, I say it depends more on gyroscopic effect from the wheels, over a certain moto's speed.
« Last Edit: 19/09/2006 11:59:47 by lightarrow »
 

Offline eric l

  • Hero Member
  • *****
  • Posts: 514
    • View Profile
Re: falling off my bike
« Reply #22 on: 19/09/2006 20:40:43 »
Well, Alberto, I think we can agree that there is not one simple explanation in this case, that at least two mechanisms have a role to play.  I doubt if there is a way to determine which effect is the most important in any possible situation here.
Of course, part of this difference of opinion started with the fact that to me a "bike" is a bicycle (if I do not have a clue to think of motorcycles in the first place).  This may be due to the fact that a son of mine has been a bicycle racer (in the youth classes only), which greatly increased my interest in the physiscs of cycling.  My experience with motorcycles is comparatively limited.
Maybe in this particular topic SoulSurfer's quotation should read "Learn, create, test and fall" - but try not to do that at high speeds.  I need discussions like these to keep on my toes.
I'm sure we'll meet again soon on an other topic.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: falling off my bike
« Reply #23 on: 20/09/2006 00:54:27 »
Ok!
 

Offline thayo

  • Sr. Member
  • ****
  • Posts: 226
    • View Profile
Re: falling off my bike
« Reply #24 on: 20/09/2006 05:42:24 »
who gives cool explanation!

lets keep trying the untried since the birth of science innovations have been like  toy but their impacts have rocked the world
 

The Naked Scientists Forum

Re: falling off my bike
« Reply #24 on: 20/09/2006 05:42:24 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums