Countersteering Confession

**erik** · 23rd October 2006, 16:41

Originally Posted by terbang

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

That's true when the bike is stationary.

Originally Posted by marty

...the wheel does not track to the right at all, otherwise the bike would initially turn/drift to the right....

The stuff I've read and my understanding of it says the wheel does track to the right. A video of a bike riding along a straight line toward a camera would prove/disprove this.

Originally Posted by terbang

Not correct. Caster angle and trail are there for directional stability. It is gyroscopic rigidity that keeps the bike upright when moving and the side stand that does it when it is stationary.
However this discussion is not about stability it is about countersteering which is control..

That's not true. Here is a quote (from http://en.wikipedia.org/wiki/Bicycle...cycle_dynamics )

"...if the gyroscopic effect of rotating bike wheels is cancelled by adding counter-rotating wheels, it can still be easily ridden."

The links posted that I've looked at have supported the idea that the front wheel tracks sideways under the bike to get it to lean. If you're still disagreeing with that after what's been posted and after reading the links, I don't think I can say anything else that's going to sway your opinion.

I think I'll have to video a bike at some point to confirm that the wheels to track right before it turns left, I think that's the only thing that will settle this. But it'll have to wait till after my exams.

Cheers to all who contributed both sides of the argument, it's an interesting thread.

**terbang** · 23rd October 2006, 18:14

OK here are a couple of fairly good articles about turning a bike:

Extract from "A Twist of the Wrist Vol II"
There are two gyros, so which one of them does what? Which end actually steers the bike? The front, right? Yes and no.
According to a number of technical reasons, laws of physics* and
engineering principles, the following is true: As long as you apply force to
the bars, the bike continues to lean further over. However, once the bike
is fully leaned into a corner, the rear end "steers" the machine. The
front-end "turns" the bike or changes lean angle but the moment the
motorcycle is leaned over and stable, the main mass of the bike -from
steering head back- determines the lean angle it will hold.

Extract from an accident prevention program in the USA:
The physics of motorcycle dynamic response to rider control input is well established. Theoretical as well as empirical studies have clearly established that a motorcycle steers in response to the rider input of a countersteer torque which causes a directional change (opposite to the countersteer) of the motorcycle. The rider inputs a countersteer and through a combination of inertial, geometric and gyroscopic effects, the motorcycle responds and begins the cornering maneuver. A brief discussion is presented but it is not the intention of the present research to derive these well established relationships in detail.
The inertial and geometric effect can be understood by examining the rider steer input during the corner entry maneuver. When faced with a desired left turn, the rider applies a clockwise torque (left bar push – clockwise headset rotation) at the handlebar which causes the front tire to steer to the right. This generates a lateral force at the front tire contact patch which causes a yaw response of the motorcycle to the right (clockwise when viewed from above). This results in roll motion to the left due to the inertial forces acting at the center of mass. This roll to the left, combined with the rider’s ubsequent steering to the left, directs the motorcycle in the desired left turn direction. This effect is easily seen when negotiating large radius turns where the desired directional change can occur over a long distance. Because of inertial characteristics, this effect (causing a lean) has a time delay when compared to the more rapidly responding gyroscopic effects.
The gyroscopic effect occurs whenever the axis around which a body is rotating is itself rotating around another axis. In the context of motorcycle directional change, the rider inputs a steering torque which causes the rapidly spinning front wheel to undergo a precession. This precession causes the motorcycle front tire to lean in the opposite direction of the rider initial steering torque input. This applies a roll moment to the motorcycle through the steering head and causes the entire motorcycle to lean in the desired turn direction. For example, a rider steer input to the right would cause the wheel to lean over to the left which contributes to the motorcycle desired lean into a left hand corner. When entering high speed turns, the gyroscopic effect is readily seen. Additionally, the gyroscopic response is present immediately after the rider initial steer input resulting in a rapid lean in the desired turn direction.

As a long time believer that it was purely Gyroscopic precession that was the only method I will concede and accept that there is another. However, I do still believe that the primary is Gyro for control. tThis lies comfortably with the Twist of the Wrist statement that the front wheel steers the bike (control) and the rear wheel turns it.

**thealmightytaco** · 24th October 2006, 17:03

I forgot all about this game! And I wont get to do it tonight either, but sometime.

Originally Posted by terbang

Didn't you do that one in your physics lessons at school. Believe me it will behave 90 deg to what you think it will.
I'm with Marty on this one. It is only Gyroscopic precession that rolls or leans the bike when countersteering.

No kidding, but when you've got 3 axis, which 90 deg? I know if you roll it over you will spin on your chair, but if you pull on it will it do the same? It's a different vector change...

(15 mins later...)

Bastard.

Lets say x and z are your left-right and forward back axis, and y is your up-down:
If you spin a wheel, holding the axle along x, and try to turn it about z, (unless you act further upon it) it will roll about y.
In other words, when you counter steer, steering out the right, the wheel will roll the bike over to the left.

Marty and co. are right in the gyroscopic effect aiding the turn.

BUT I still think the falling broomstick effect plays a part. Might try find the radius of gyration and weight of your average wheel and crunch some numbers and see how much each effect plays in the turning of a corner. Just so I know.

I must concede though, most humbly, that the gyroscopic effect would lean the bike over all on it's own if given the chance.

**thealmightytaco** · 24th October 2006, 17:08

And I just saw terbangs last one... I'm feelin' it now.

**Jamezo** · 24th October 2006, 17:51

I don't think there's any chance of saving you lot, so I'll guess I'll just let you live out your delusions, meanwhile the man with the impossible (according to your interpretation) contra-rotating motorcycle is laughing his arse off, and a broomstick falls in the woods with nobody to hear it....

PS. That broomstick idea stuff was a load of shite.

**Ixion** · 24th October 2006, 17:58

Struth. I'm glad I started riding before all this stuff was invented.

But - a question
As I understand what people is sayin :

If you have a rotating mass (ie wheel) , and you turn it to the left (via the bars) , it will make the wheel lean over at 90 degrees to the turn - ie , bank to the right. I remember enough high school physics to go along with that.

Initiate turn to right, wheel (and thus bike) banks over to left. Then the axle line and wheel form a truncated cone, so the bike rolls around that and turns the corner.

Well and good.
But : this works for cruisers too, right ? I'm sure it does. And given that a crusier has tyres as wide and big (and nearly as flat) as , say, a Morrie Minor, why doesn't the same thing happen when you turn the wheel of the Morrie to the left (via the steering wheel) . Morriis wheel is rotating too, is as big and heavy as a bike wheel. Why doesn't turning the Morrie wheel(s) to the left cause the car to bank over and head right ? Or does it?

**terbang** · 24th October 2006, 18:05

I guess its because its got 4 wheels..!

But I reckon if you were to get an old morrie up to say, 160 kays (down a really really steep hill) and then wracked the steering over to the right. I suspect you may find some sort of roll to the left.

**MacD** · 24th October 2006, 18:10

Originally Posted by Ixion

Struth. I'm glad I started riding before all this stuff was invented.

But - a question
As I understand what people is sayin :

Well and good.
But : this works for cruisers too, right ? I'm sure it does. And given that a crusier has tyres as wide and big (and nearly as flat) as , say, a Morrie Minor, why doesn't the same thing happen when you turn the wheel of the Morrie to the left (via the steering wheel) . Morriis wheel is rotating too, is as big and heavy as a bike wheel. Why doesn't turning the Morrie wheel(s) to the left cause the car to bank over and head left ? Or does it?

I bet if you got the Morrie up on two wheels via a ramp it would behave exactly as a bike does, in other words you'd use countersteering to alter the roll attitude and therefore control how it turns.

**marty** · 24th October 2006, 18:11

i think you will find that there is still GP at work on your morrie, however the axle is fixed in the horizontal plane, and the force of the steering arm overcomes the force of the GP. if you took the wheel off, and spun it like a bmx wheel, you would experience the black magic......

**Hillbilly** · 24th October 2006, 18:24

Here's some more on the subject:

Leaning by applying a gyroscopic force
Gyroscopic effect also plays a role in banking a motorcycle. When a torque application tends to modify the plane of rotation, gyroscopic effect produces a rotation whose axis is perpendicular to the axis of the applied torque. By turning the handlebar to the left, gyroscopic effect of the front wheel causes the motorcycle to bank to the right with respect its roll axis. Likewise, a turn of the bar to the right will instigate a lean to the left. We have examined two methods of changing the direction of a motorcycle and in both cases the initial input at the handlebar must be in the direction opposite to that desired. Happily, the effects of these two methods work in concert. They could have worked in opposition such as in the hypothetical case in which the rear wheel pivots to provide steering.

Definition of countersteering
If countersteering of a motorcycle consists of orienting, for a brief moment, the front wheel in a direction opposed to that in which one desires to go, then countersteering is the source of all significant changes of direction.There exist certain types of controllable single-track vehicles which make no use of gyroscopic effect (with blades, with skis, automobiles cornering on two wheels, two wheels with counter-wheels).

Justification of the term countersteering
The term countersteering is perhaps poorly chosen. While in automobile driving it describes a procedure for recovering from a skid, in motorcycling it refers to a procedure of initiating or creating a change of direction. Perhaps a less ambiguous term is needed.It is possible to ride a motorcycle safely over a long period without even being aware of this characteristic. Several motorcyclists who have not been exposed to recent rider training courses completed this operation successfully without being aware of it, as are the majority of bicyclists.This procedure of countersteering is taught in rider training courses as a technique for avoiding a sudden obstacle. Often, the student discovers for the first time the necessity to turn the handlebar momentarily in the opposite direction to the one desired. Certain students continue to believe that countersteering is valuable only for obstacle avoidance. The test of the Société de l’Assurance Automobile du Québec (SAAQ) for a motorcycle operator’s licence contains a specific evaluation of this manoeuvre.

There are also some pics as well...

**Ixion** · 24th October 2006, 18:24

Well, maybe. But has anyone ever experienced having a car go left when you turn the wheel to the right ?

**MacD** · 24th October 2006, 19:31

OK, one last attempt at convincing the disbelievers that gyroscopic forces, while present, are not essential for, or the primary cause of turning in bikes when countersteering.

From: J Fajans, (2000). Steering in bicycles and motorcycles. Am. J. Physics 68(7): 654-659.

"Figure [3](d) shows the contributions of the trail torques and of the gyroscopic torque to changing the steering angle. While the gyroscopic torque is non-negligible, it is much smaller than the trail torques and somewhat smaller than the handlebar torque. Thus, in accord with Jones' observation that a bike equipped with a gyro nulling counter-spinning wheel behaves much like a normal bicycle, the "feel" of the bike is dominated by trail"

"Contrary to the assertion in reference 3, gyroscopic action plays no role in leaning the bike. However, as shown in Figure 3(d), and in agreement with reference 3, it does play a role in steering the front wheel back towards the desired direction"

"In any event, gyroscopic forces play little role in leaning the bike over, though they do help set the steering angle. The appealing notion that gyroscopic forces are central to bike behaviour, often repeated in papers and textbooks, is incorrect"

So, gyroscopic forces stabilise a bike in straight line travel, but are not necessary for turning. They do aid the recovery from a turn, but other forces produced by the trail setup and rotation are significantly larger when initiating a turn.

Believe it or not!

**marty** · 24th October 2006, 19:44

i have still yet to see whether the opposing gyro (at speed) negates the pulling on the left bar to instigate a right turn. i have only seen that it makes the push bike handle in a straight line in a similar fashion. someone please link me....

and the graphs do not appear to nominate the trail - we all know that a steeper headset tends to mean a quicker turn-in, likewise a chopper-style headset means the wheel literally falls in - we're not disputing that. what if the headset was vertical?

**terbang** · 24th October 2006, 20:05

I'm sure you see this in the Pitts Marty. Used to tow gliders in cubs (1978). ZK-BOV appears in my logbook along with ZK-BPE at that time. They were PA18A models, lyc 320 powered and swinging a decent sized prop (compared to the old PA18). They were american engines spinning clockwise viewed from behind. After a good days towing where the gliders mainly kept me straight on takeoff, I would fly the aeroplane home without a glider. Guaranteed to get a nice shock as I, with lazy feet by now, raised the tail and she would rapidly swing left thanks to the Gyroscopic precession on the prop.
Gyroscopic precession is alive and kicking and though not visible it is easily felt and has had many a young taildragger pilot dancing on rudder pedals.
Oh sigh those were the days, now I fly a Boeing and the only real action my feet get, is walking to the carpark..