North Auckland Street Skills - NASS

[R-Soul]

I saw this comment on the california superbike school forums site - its very interesting reading in general. Perhaps we could do this one one day at teh NASS events?

PS teh website is http://forums.superbikeschool.com/in...lter=all&st=15

"For all of you,

This is an interesting topic.
Maybe the following will be of interest to you.

I have been a motor instructor for more then a decade and am currently working as an examinator in Holland.

So when people are taking a test drive to get their driving license they have to show me their ability.

One of the manoeuvers the kandidate has to execute is swerving and avoiding an obstacle.
They must approach a gate of 1meter wide ( 2 cones )with a speed of 50 km/h and then swerve left around the obstacle ( 4 cones ) wich is placed at a distance of 15 meters from the gate and 2 meters to the left of the left hand cone of the gate.
After swerving around the obstacle they must get back in to their original riding line within 18 meters of the obstacle.( 1 cone )
The kandidate is only allowed to shut down the throttle and steer when his bike is in the gate.
He/she is not allowed to brake or downshift.

Properly executing this excercise means quick steering, there's no other way to do this.
We find this to be a fantastic excercise wich gives the new motorcycle rider a lot of ability and control in a variety of situations.

The key things in a proper execution are: ( as far as we're concerned )
1 A firm grip of the tank with your knees. ( try to get a dent in the tank )
2 As many contactpatches between the bike and your legs.
3 Shoulder and arms not tightened but relaxed.
4 The bike should move beneath you, the upper body stays almost upright.
5 A firm but short steering input of the handlebar.
6 And most important of all, where you look is where you go, so look around the obstacle, not towards it.

Now all you need is a piece of quiet asphalt and 7 cones, or beercans or whatever you can use to practice the excercise.
Sorry but you have to convert the metrics to your system.

P.s. If you're going to practice; start at slower speeds first. Work your way up from about 30 km/h

Would love to hear any comment on this.

Mike Kromjong
Holland"


It might have been done already? Anybody?

[p.dath]

What have you been reading? I would be interezted to know how it works in simple mechanical terms without gyroscopics coming into play?

This is the article I like best:
http://en.wikipedia.org/wiki/Countersteering

[p.dath]

I am not sure why you say it takes so long fo rcounter steering to click. Nobody ever taught me about it,l and when I figured it out for myself, it was instantaneous
....
PS And I dont see what there is to "get" about counter steering. You want to go right at speed? Push forward on the right bar. You want to go left at speed? Push forward on the left bar. No other instruction needed. Instant control.

Perhaps you got it quickly.
My personal experience and those of people I have helped has led me to the conclusion you need about three months of riding practice before you can really start counter-steering with intent.

For example, last Wednesday my personal perception is that the biggest issues were with body posture (such as wrongly making arms rigid), throttle control [on off on off] (to keep the bike stable), and not looking were you wanted to go.

I don't feel "qualified" to help a lot of the people out on Wednesday (which is why we have people like Richard and BigDog [??]), but even so, I still pulled a rider with one month of experience to one side and spent about 10 or 15 minutes with him helping him out. We went to the other car park which was less crowded. He "got" counter-steering, but his big problem was throttle control which kept making him wobble when trying to counter-steer, and upsetting the bike. Didn't take long to get him up to speed to re-join the group. After another month he'll find he wont be having to think about throttle control because it will be automatic. He'll be able to concentrate on something else then ...

[R-Soul]

Perhaps you got it quickly.
My personal experience and those of people I have helped has led me to the conclusion you need about three months of riding practice before you can really start counter-steering with intent.

For example, last Wednesday my personal perception is that the biggest issues were with body posture (such as wrongly making arms rigid), throttle control [on off on off] (to keep the bike stable), and not looking were you wanted to go.

I don't feel "qualified" to help a lot of the people out on Wednesday (which is why we have people like Richard and BigDog [??]), but even so, I still pulled a rider with one month of experience to one side and spent about 10 or 15 minutes with him helping him out. We went to the other car park which was less crowded. He "got" counter-steering, but his big problem was throttle control which kept making him wobble when trying to counter-steer, and upsetting the bike. Didn't take long to get him up to speed to re-join the group. After another month he'll find he wont be having to think about throttle control because it will be automatic. He'll be able to concentrate on something else then ...

Well done - anybody that spreads theory around is doing good I reckon- it makes peple think about itand experiment and try different things - instead of just doing what they have always done and stay ignorant.

I checked that article out from Wiki- nice one as it gives numbers (I like numbers!).
I was surprised when I read that t the gyroscopic precession is aonly a small part of the countersteering effect (3.5Nm as opposed to 30Nm of torque on the bike). However he did not mention teh weight of teh bike presumed to be the figure of 30Nm, and I wionder about the assumption of 1 degree of turn in half a second. To me, 5 or 10 degrees of turn in half a second seems more likely, or 3 degrees in 0.2 of a second? That would multiply the gyroscopic effect substantially (up to ten times?).

They also dont mention what the gyroscopic effect would do to keep the bike upright against the lean angle of the bike without the turning of the bars (i.e. if there was lean angle alone, but no sudden turn on the bars creating the precession moment on the bike's centre of mass) - although they are inextricably linked so I guess that argument is moot.

Thanks for the link.

While we are at it, can anybody explain why "chopping" the throttle mid turn causes the front end to break away?
After all the same forces apply, but the speed is decreased, so the forces acting outwardly on the bike should decrease, not increase them to cause them to overcome the friction of the front tyre?

Perhaps teh weight shift to teh front of teh bike causes the forks to dip, and the steering geometry to change, causing a quick change in turn in (i..e a suddenly decreasing turn radius) that increases the cenripetal forces due to teh sudden changes in radius? To my mind then, this effect would not be seen in bicycles with no suspension? maybe a cyclist can confirm this?

[p.dath]

While we are at it, can anybody explain why "chopping" the throttle mid turn causes the front end to break away?
After all the same forces apply, but the speed is decreased, so the forces acting outwardly on the bike should decrease, not increase them to cause them to overcome the friction of the front tyre?

If we limit the discussion to only counter-steering, as opposed to cornering in general; the bike is an upside down pendulum - all the weight is at the top and it pivots about the bottom. As a result it is unstable and liable to fall over without constant input from the rider.
To do counter steering your centre of mass has to be offset from the bike (either to the left or the right - actually this is the entire point of counter-steering). You do this to deliberately de-stablise the bike so that it can turn. This is what makes the bike lean over.

Once the bike is leaned over you have to do something to stop it falling over. This is where the throttle comes in. You have to apply sufficient throttle which tries to push the centre of mass straight ahead (correcting the lean), while gravity is busy trying to make you lean even more. If you suddenly close the throttle the force on the centre of mass which tries to straighten the bike up is reduced, but gravity stays the same. Now something bad is going to happen ...
It is also why if you apply when you apply more throttle at the end the bike straightens up, because the force becomes greater than that of gravity.

Gryroscopic forces do come into play, but they are a minor part of the equation (depending on the weight of the rider and the weight of the spinning wheels - but usually not a big percentage of the equation).

This is easier to demonstrate sitting on a bike. I'll try and come along this Wednesday. Find me and I'll show you.

[R-Soul]

If you suddenly close the throttle the force on the centre of mass which tries to straighten the bike up is reduced, but gravity stays the same. Now something bad is going to happen ...
It is also why if you apply when you apply more throttle at the end the bike straightens up, because the force becomes greater than that of gravity.

Sure I get that the throttle controls the sped of the bike, which establishes the size of the centripetal force (acting on the combined centre of mass of bike and rider) to push the bike outwardly. This centripetal force is balanced by that component of the gravitational force acting inwardly at teh same centre of mass. But these forces are acting as a moment about the tyre contact patch. Think of the bike and rider as a lever about the contact patch (i.e. extending from the contact patch to their combined centre of mass). If speed decreases for given amount of lean, then the centripetal force decreases and the lean inward increases. If the speed increases, the cenripetal force increases and the lean decreases (i.e. bike goes more upright).

But why does chopping the throttle cause a breakaway AT the contact patch, and not just a sudden change in lean angle? Especially as the centripetal forces are decreasing, so the total outward force decreases?

[Badger8]

All this discussion (i didnt read most of it to be honest) is merely academic. i read all about it when i started riding too, but the best thing i ever did was try it out as follows.

Go to an empty road, cruise along at about 50 kph. Loosen your grip right up on the bars, and GENTLY push forward on one of the bars and see which way you go. Slowly increase the pressure with repeated times, and you will soon get the feel of how your bike tips in.

I did this on my third time out on a bike, and suddenly everything i had been reading didnt matter anymore. I didnt care how it works, all that matters is that it works! I had been doing it subconsciously when i leaned into corners anyway (pushing slightly forward on the inside bar) but now that i had a feel for it and could do it intentionally, my cornering improved exponentially.

The theory side of things has been covered a lot at NASS in the past, and i'm sure if you speak up and ask, someone can have a long chat about it and show you how it works on the bike before heading out. The instructors can only give you want you specifically want if you ask!

i am off work ill at the moment, but hoping to be back by next week at the latest, and would be happy to run you through any theory you like, then send you out to put it into practice

[R-Soul]

i am off work ill at the moment, but hoping to be back by next week at the latest, and would be happy to run you through any theory you like, then send you out to put it into practice

I know how to do it. I am just interested in the theory - if you could answer my question below I would be happy.

[p.dath]

Sure I get that the throttle controls the sped of the bike, which establishes the size of the centripetal force (acting on the combined centre of mass of bike and rider) to push the bike outwardly. This centripetal force is balanced by that component of the gravitational force acting inwardly at teh same centre of mass. But these forces are acting as a moment about the tyre contact patch. Think of the bike and rider as a lever about the contact patch (i.e. extending from the contact patch to their combined centre of mass). If speed decreases for given amount of lean, then the centripetal force decreases and the lean inward increases. If the speed increases, the cenripetal force increases and the lean decreases (i.e. bike goes more upright).

But why does chopping the throttle cause a breakaway AT the contact patch, and not just a sudden change in lean angle? Especially as the centripetal forces are decreasing, so the total outward force decreases?

The force caused by the throttle mostly acts at the centre of mass - not at the tyre contact patch. Although of course, the rear contact patch is where the power is delivered.

When counter-steering the bike pivots at the tyre contact patch though. So pivots at the bottom, but the force acts half way up the bike. Hence it tries to push the bike over. The bike is pretty much trying to rotate longitudinally. The front tyre will continue to hold unless this rotational force becomes too great.

[R-Soul]

The force caused by the throttle mostly acts at the centre of mass - not at the tyre contact patch. Although of course, the rear contact patch is where the power is delivered.

When counter-steering the bike pivots at the tyre contact patch though. So pivots at the bottom, but the force acts half way up the bike. Hence it tries to push the bike over.

Right- you've got it. Forces caused by the throttle (and velocity) act at the centre of mass. So why does chopping the throttle suddenly in a corner cause the front wheel CONTACT PATCH to break away? Especially as it will be reducing speed?

Do you see my question now?

[MarkH]

the centripetal force (acting on the combined centre of mass of bike and rider) to push the bike outwardly.

Other way around - centripetal force is the INWARD force: http://en.wikipedia.org/wiki/Centripetal
The outward force is inertia (sometimes mistakenly named centrifugal force) which causes an object to tend towards carrying on in a straight line.
The greater the centripetal force the tighter the turn.

It's all simple fizziks really!

[R-Soul]

Other way around - centripetal force is the INWARD force: http://en.wikipedia.org/wiki/Centripetal
The outward force is inertia (sometimes mistakenly named centrifugal force) which causes an object to tend towards carrying on in a straight line.
The greater the centripetal force the tighter the turn.

It's all simple fizziks really!

OK thanks for the claririfcation (my engineering terminilogy is fuzzy - its been a while). So its the same number but in an opposite direction.

The friction force at the contact patch must equal the centripetal force required to keep the bike on the corner.

And the opposite force to the centripetal forec (call it "inertial" force) acting as a moment around the contact patch must balance the inward component of the weight of the bike (which must also equal the centripetal force for there to be equilibrium and no change in lean angle).

When the throttle (i.e.velocity) increases, so does the centripetal force required to keep the bike on the corner, since this is will increase the inertia. But when the throttle is reduced, the velocity changes downwardly, reducing the inertial force, and allowing the bike to lean in more as the weight component is no longer balanced. This is why you could slow down as the radius of a curve decreases to increase your lean angle (or alternately you could counter steer more).

Rolling off gently is fine- but why does chopping it result in a breakaway at the conatct patch?

I still have no answers?

[p.dath]

Rolling off gently is fine- but why does chopping it result in a breakaway at the conatct patch?

Perhaps lets clarify the question. Are you meaning a loss of traction? I don't think you should be loosing traction while counter-steering.

[R-Soul]

Perhaps lets clarify the question. Are you meaning a loss of traction? I don't think you should be loosing traction while counter-steering.

Actually my original question had nothing to do with CS. I just wanted to know why you tend to have highsides from a loss of traction if you chop the throttle mid corner. Throttle control is all important mid corner- I want to know why - the fizziks of it.

[R-Soul]

Perhaps lets clarify the question. Are you meaning a loss of traction? I don't think you should be loosing traction while counter-steering.

PS d.path are you going to be at the riding class on Wednesday? It would be cool to meet you eventually.

I need to get a pink slip first...but its all in the interests of safety so its essential right!!?