Lnewqban
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Posts posted by Lnewqban
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The center of gravity of the bike does not change while going uphill or downhill.
The vector weight tilts aft and forward, loading one tire and unloading another.
The whole purpose of throttle control while cornering is to distribute the loads on each tire according to bike design.
That is a 40% of the total weight on the front contact patch and 60% on the rear contact patch.
An acceleration of 0.1 to 0.2 G makes that vector weight tilt aft enough (6 to 11 degrees) to achieve that ideal load distribution.
A hill with 1:4 gradient has 14 degrees and exactly that is what the vector weight tilts.
As you can see that is a little more than the ideal distribution of weight when going uphill with zero acceleration (maintenance throttle only).
The rear contact patch is the weakest link in that case and too much acceleration could overwhelm it while cornering fast.
Going downhill that steep is much more critical, because your front contact patch is loaded with around 70% of the total weight; with more if you are breaking to keep speed.
For both cases, the solution is slowing down your entry speed according to these scenarios (way more for downhill cornering) and not applying throttle control (smooth acceleration) as for horizontal track riding.
While going uphill or downhill, the tires have less available traction as well due to a reduced normal force respect to the pavement.
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Lnewqban .. please don't misunderstand that I'm ungrateful for your advice / explaination because I said it confused me. If my "internet tone" sounded that way, I apologize.
Light bulb !
So I think coming back to my original question, my drill isn't missing any pieces. I was over analyzing and over complicating things. Doh!
No apologies needed, we are good.
That light bulb makes me happy.
Yes, it is a complicated process when we think about it, but when we learn to feel the bike and the road, riding well becomes a natural sequence that flows smoothly.
I have found this old video, which summarizes our discussion:
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Lnewqban .. your questions makes me go "hmm". You're certainly right that I do not and can not directly select an exact lean angle. On reflection, its not like I currently go into a corner now thinking .. 23 deg for this left turn .. 33 degree for the next right. So I certainly can't 'choose' to add exactly 5 more degree of lean angle consciously.
Now this makes me ask myself, so how am I mentally selecting my lean angle for each turn currently ? Perhaps once I am able to answer this question, everything else will become clear.
You did say that lean angle is a "natural result" of speed and radius. I'm sorry but that is not making sense to me. A bike with no rider on it doesn't want to lean or turn. It naturally wants to run straight and up right. So then it becomes the job of the rider to set the lean angle required via steering and the rider can certainly select incorrectly less lean angle and run off track, or too much lean angle and risk a low side. Or at least this is my understanding of it. So I'm having a hard time understanding how lean is a natural result.
This brings me to steering input. I push the bar at an angle and have never thought to measure how fast my input was. I've heard of Keith's quick flick steering but have not tried it yet. Something about that technique is very intimidating to me. Maybe because subconsciously I don't know how I select a lean angle, I default to a slower steering to allow myself time for corrections ?
Please, excuse me if my attempts to explain the forces of circular movement have confused you.
I will keep it simple, because I believe that it is extremely important in your case to become familiar with the dynamics of any turn.
How am I mentally selecting my lean angle for each turn currently?
Like everyone of us, you are using your sense of balance to keep the bike from falling down, as you are transferring from one state of balance (for vertical force pulling you+bike / before the turn) to a new state of balance (for diagonal force pulling you+bike / during the turn).
Just imagine that you are standing on a platform that is still (but can turn) and that you have a broom balancing upside-down on the palm of your hand.
You are using your sense of balance to keep the broom from falling down and the broom remains more or less vertical.
Next, the platform begins a slow rotation.
You keep using your sense of balance to keep the broom from falling down, but now the broom adopts a balance position that is not vertical anymore.
I don't need to tell you how much faster I am going to spin the platform, you still will be able to keep the broom from falling down (as you will see the broom adopt a balance position that is more diagonal and away from vertical).
So then it becomes the job of the rider to set the lean angle required via steering and the rider can certainly select incorrectly less lean angle and run off track, or too much lean angle and risk a low side.
Let's not to discuss the process of transition from straight to circular trajectory and vice-verse for keeping it simple and focused on lean angle.
Unless forced to move in a circular trajectory, all objects (including motorcycles) either remain in repose or moving along a straight line.
The rider did force the bike to enter a curve of the track (to initiate a circular trajectory).
The balance of forces (weight and centrifugal) took over and kept the bike turning.
At this point, think of a rolling coin describing a circle by itself.
In the same way, any properly set motorcycle that is banked (in balance respect to the lean angle) and describing a circular movement will remain on that circular path with minimum input from the rider.
Your statement is not accurate because the rider cannot select a lean angle; the job of the rider (after counter-steering to initiate a lean) is to set the precise steering deviation between both tires that is needed for the bike to follow the curve of the track (let's assume that he/she is following a constant radius curve of a very narrow track; hence, no apex and the ideal single steering input) ..... and to keep balance (finding the proper lean angle via his/her sense of balance).
Once the proper lean angle is reached, all forces are balanced (like in the case of the rolling coin) and the rider does not need to apply more steering inputs until the end of the turn.
The rider can certainly select incorrectly less steering input and run off track (carrying less lean angle), or too much steering input and over-turn (carrying more lean angle).
In those cases, the rider is selecting a turn of less or more radius, and as a consequence, the lean angle will be less or more (if the speed remains the same).
I push the bar at an angle and have never thought to measure how fast my input was.
That is part of the transition from vertical balance (straight trajectory) to leaned balance (circular trajectory).
The speed with which the transition happens (how quick you toss the bike into the turn) does not depend on how fast but for how long the counter-steering input is applied.
The slower this process takes, the more lean angle you will end up with.
The reason is that it is like the rider selects incorrectly less steering input during the first third of the turn (running off track / carrying less lean angle) only to be forced to select more steering input during the second third of the turn (over-turning / carrying excessive and dangerous lean angle around the apex).
Think of the bike describing a semi-ellipse rather than a semi-circle.
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......... If I follow step 1-3 and get into the corner faster with the same lean angle I use with my current slower speed, my line will widen and I'll run off track.I have to lean more ( which is easier said that done ) to offset the higher speed, but when should my lean be 'completed' I assume between step 2 and step 3 since I would want to avoid adding throttle and lean angle at the same time. Just seems to me there's not much time there to work on figuring out how much lean angle to add along with adapting to the higher speed. Seems like there's a middle step missing from this drill........I believe that it is very important to understand that you do not directly select a certain angle of lean.
That angle is the natural result of two things only:
1) The speed of the bike during the time that the bike is turning.
2) The radius of the line that the bike is describing on that curve.
If in a vertical position, you and your bike are in balance while moving along a straight line because the force of gravity is pulling down in a vertical direction.
As soon as you and your bike start moving along a circular trajectory, the combination of the centrifugal force and the weight results in a force that is greater than the weight and that pulls along a diagonal angle (an angle between vertical and horizontal, which equals the lean angle).
Either you and your bike get aligned with the direction of that force, achieving a new balance, or you fall.
Returning to 1 and 2 above, radius is imposed by the geometry of the curve; therefore, speed is the only factor over which you have control.
You determine your entry speed for a particular curve and the lean angle naturally follows that decision; then, subconsciously you adapt the inclination of your body and bike to meet that angle ........ or you and bike fall.
If seating centered on the bike, your body weight will always be pushing perpendicularly to the surface of your seat.
As the lean angle increases, that force pushing against the seat (and compressing the suspension of the bike) also increases.
If you reach 45 degrees of lean, that force pushing against the seat will feel 140% higher than the force that you feel when riding along a straight line.
The limit you are hitting is psychological rather than physical.
Our mind is wired to keep balance for forces pulling straight down: our own weight.
You need to learn to keep balanced for the diagonal forces explained above, which are not natural to your mind: motorcycling is not a natural activity, it must be learned.
Following the basic principles of cornering explained in "A twist of the wrist", you will not reach the physical limit of traction for any lean angle between zero and 40 degrees.
Your mind, however, will naturally be in alarm mode for any angle beyond 15 to 20 degrees.
Higher entry speed results in higher lean angle: as you fear uncomfortable lean angles, you over-cautiously moderate your entry speed.
For a better understanding of these things, I recommend you reading these two articles:
http://forums.superbikeschool.com/index.php?showtopic=310
http://forums.superbikeschool.com/index.php?showtopic=3723
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What would you estimate the actual, combined lean angle is when Lorenzo has his bike leaned over 64 degrees in addition to hanging off?
T-McKeen's post #15 fully coincides with what I have learned about Physics.
Please, Eirik, take a look at these calculations:
http://forums.superbikeschool.com/index.php?showtopic=3324&page=3
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Very interesting subject!
I use my ears and skin vibration sensors rather than my eyes for anything related to the bike: rpm's, miss-shifts, mechanical things, deceleration and acceleration rates and shifting (up and down).That liberates my vision for traffic situation and for road traps.The farther ahead I can spot those, the more time I have to adjust my trajectory, lane or position.I also use my hearing as a support for traffic abnormalities, like two-wheeled rockets approaching too fast, cars/trucks with mechanical or tire's issues, 18-wheelers, emergency vehicles, hard braking's and accelerations, etc. -
Can you give an example of point 3, p. 76 of Twist II?
The point states that track positioning is useful when: " A slow turn-in, under-braking turn entry when positioning the bike quickly for the turn point could overload the front tire and cause the front wheel to lock".
I understand over-braking while turning will cause a loss of traction, or over-braking can lock up the front wheel, but I'm not understanding this statement. The statement gives me visions of beginning a fast turn early and trail braking (slow turn-in) , positioning the bike for a turning point then making a quick turn in a late apex, decreasing radius turn. Not sure.
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Hey Guys,
So i highsided a month ago....broke my left femur and ankle.Recovering now........
Very sad to read that, Stroker.
Hope that you fully and quickly recover.
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Lnewqban can you expand a bit? I did think that the "help" if you like was only while going from left turn to the central point before the right turn started, the source of the "centrifugal" force beign teh kart's natural desire to go straight on not round a corner
That help would come from the suspension returning back to normal or unloaded condition as you turned the steering wheel from left to center.
If I understand correctly, the go-kart has no springed suspension and any help would come from the limited spring effect of tires and chassis deformation under load.
If that is the case, what made the go-kart "roll" left-to-center was the elimination of the lateral force of the left turn times the vertical distance between the center of mass or gravity and the contact patches of the tires.
What resisted that "roll" was the moment of inertia of the go-kart plus your body about the rotational axis (nose to tail).
To learn more about the moment of inertia or angular mass:
http://en.wikipedia.org/wiki/Moment_of_inertia
In the case of the bike going through a chicane, the forces of turning are the same, but we quickly locate both contact patches of the bike in line with the direction of the lateral force plus the weight.
How quickly? - As quickly as the bike changes its trajectory from straight to circular or vise-verse.
In order to keep balance, there cannot be any delay of the bike's roll respect to the change of direction of the resultant force.
That is not the case for the go-kart, which does not roll-over as long as that resultant force points down between left and right contact patches.
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........... I also found that in the switch from left to right, it was very snappy indeed. I think this is because while the kart was turning left, it really wanted to go straight on, so when I turned it right instead, I was going the way it wanted to, at least until it was past the middle point and then turning right. Was this really the case? ..........
That was not the case.
The lateral forces happen instantaneously with the deviations from a straight trajectory.
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Thanks for the advice HF and everyone else.Feel free to point out even the slightest mistakes.I fear there are many.
Take a look at this:
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I'll add a few comments.
.........Very good observations, YellowDuck!
The coefficient of friction between rubber and concrete is lower than between rubber and asphalt; hence, less lean angle can be reached before sliding one or both tires.
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3. How do i differentiate between turning more and leaning more? I am not sure what makes the bike lean more and what makes it turn more? Or maybe i am confused in this matter because i felt i was falling off the edge of the world when i tried running circles in earnest.
Stroker,
You were describing a circle of constant radius; therefore, you were turning the same.
In order to turn around a tighter circle (smaller radius), you need to turn the handlebar more.
While describing a circle of constant radius, more speed requires more lean angle and vice-verse.
The bike must be leaned in order to keep balance between the weight and the lateral (skidding) forces that act on both contact patches when turning.
Those lateral forces are higher for higher speeds and lower for lower speeds.
Use these threads as reference:
http://forums.superbikeschool.com/index.php?showtopic=3303
http://forums.superbikeschool.com/index.php?showtopic=3320
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It seems to be related to the rear suspension: insufficient compression damping and/or excessive tire pressure.
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.......... you're in a long "bowl" type of corner..
What a bowl corner is?
This thread may help you as well:
http://forums.superbikeschool.com/index.php?showtopic=3883
Fastest possible cornering: Enter slow, keep proper acceleration, leave fast.
Keeping proper acceleration during the whole turn is more than an arbitrary rule: it keeps proper forward-aft weight distribution, proper suspension range, proper ground clearance, neutral steering.
In other words: sacrificing entry speed for keeping acceleration is not a bad thing.
Chapters 1 to 6 of TOTW 2 explain the physical reasons.
How much?
Around 0.1 to 0.2 G of acceleration = Constant increment of speed along the turn of 2.2 to 4.4 mph per each second that the bike is leaned and turning.
"Smooth 5th gear roll-on in the 4000 ~ 6000 rpm range on pretty much anything above 600 c.c."
Once you open that throttle, "it is rolled on evenly, smoothly and constantly throughout the remainder of the turn."
If the curve is too long or weird-shaped to keep this rule practical, then you split the curve into two or more sections.
You enter each section slow and leave it fast, reduce lean angle, shave speed off, then repeat for the next section.
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Are you saying it is because my throttle hand is close to the tank, i subconciously don't want it to hit the tank and therefore cant get myself to full lock on the right side?
I am not saying so.
The reason of those steering/frame's limits is to prevent the handlebar from hitting the tank.
Again, the problem may be the awkward position that your right wrist adopts at full right lock, while trying to keep fine control over the throttle.
Before turning the steering all the way to the right, try grabbing your throttle like you grab a screwdriver, even if you keep one or two fingers on the front brake's lever.
Remember to keep a steady throttle while your rear brake controls the lean angle.
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The problem may be in the way your right hand holds the throttle grip and in the way your right foot operates the rear brake yet is ready and free to stop any eventual fall on the right side.
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This is not about the bike's handling, but how I perceive speed. Let me give two examples:
Great post from Hotfoot!
If the brake-gas transition is not your problem, it seems that your perception of deceleration eases your fears, while acceleration makes you feel uncomfortable.
That perception is far from the Physics that apply to your street bike: riding a bike is far from natural.
Most conditions for street riding will accommodate an extended overload of the front tire.
There will be turning situations and conditions of low traction in which opening the gas will help and braking will make things more difficult and potentially dangerous....., especially if 100 mph is a regular speed.
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Thank you, Dylan!
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Just read a little further in Twist II and your answer will be there:
You get the gas on at the earliest possible moment in a corner. This does not mean at the apex, right before the apex or right after the apex, or at any particular part of the turn, it means as soon as possible.
To meet the throttle standard, steering is completed before you start to get it on.
Thanks!
Can we say then that as soon as possible is the moment when the steering is completed?
Are there other factors other than steering for which the rider should wait or that could make the opening of the throttle non-possible?
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This is a great video, Dylan!
Perhaps it serves as a good basement for you and other coaches and experienced riders to explain what has been confusing to me for long time: the point along the turn to open the throttle.
According to Chapter 5 of "A Twist of the Wrist II":
"When? - As soon as possible. You get the gas on at the earliest possible moment in a corner."
When do you get to the throttle?
How can it be too soon?
What is the sign that indicates that "possible moment"?
Most videos found in the web consistently show a clear braking or deceleration of the bike all the way precisely to the apex.
It seems that, for these riders, the apex is chosen as that magical "possible moment".
According to what I understand in the book about best range of suspension and optimum traction during cornering, decelerating while leaning and turning only overloads the front tire.
Although being so popular in track days and races, is that a wrong practice?
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I'm a little confused by this.
If you accelerate mid turn, the bike will come up if you don't do anything to stop it, right? The shear force on the front tire from the ground, due to the acceleration of the rear tire, pushes on the front contact patch and does the same thing (creates the same resistance at the contact patch) as countersteering the bike up does -- at least, that's my understanding.
If that's the case, then if you accelerate, the only way to keep the same radius is to "force" a bigger lean angle by countersteering. Right?
Also, by bring the bike out of "balance", do you mean away from the point that it is turning without you needing to maintain pressure on the bar? (As if it is "balanced", once you initiate the turn, you shouldn't have to maintain any pressure to continue at that radius.)
I understand and agree with your explanations: what I tired to say is that finding a balancing lean angle is the last step of the sequence: you decide radius of turn and speed and the required lean angle will follow, rather than the other way around.
The frontal contact patch may be the link of a chain reaction, but not the reason for the bike standing up while accelerating: a wheelie under acceleration tends to run wide as well.
Rolling on two or just one wheel, the principle is the same: for the same radius of turn, more speed increases centripetal acceleration and vice verse.
That centripetal acceleration (and an apparent force that draws any rotating body away from the center of rotation, caused by the inertia of the body) is applied to the center of mass.
Four, two or just one contact patches is all we have to resist that apparent force and to continue following a curve.
What brings the lean into this is the fact that there is certain distance or height between the center of mass and the contact patch(s).
A couple of opposite forces separated by certain distance always create a torque.
That torque would make the bike tip over the external side of the turn.
The trick that we use to prevent that from happening is to lean the bike toward the internal side of the turn until we find a new balance.
That is the type of balance to which I referred in my previous post: a balance of lateral forces and torques.
The tool that we have to induce and find that lean angle is the counter-steering.
Just like 90 degrees is the only angle that balances the bike vertically (while moving along a straight line), only one specific lean angle will correspond to balancing the dynamic lateral forces introduced by the inertia of bike plus rider while describing a circular line.
A locked steering will allow you to sort any combination of radius/speed; however, once the magic balance is achieved, if you accelerate (or slow down), your bike will fall outward (or inward) as you cannot re-adjust your lean angle (and re-balance) via counter-steering.
The steering balance that you mentioned is another thing: some bikes are under-steering (tend to turn wide and you have to keep pressure on the outside handle), some are neutral and some are over-steering (dangerously tend to tighten the line by themselves, reason for which you have to keep pressure on the inside handle).
Those tendencies are determined by the geometry of the bike and the steering and by the profile of the tires.
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............. I was increasing my lean angle still further and therefore was able to increase my overall speed .................. I was already in a corner and wanted to tighten up the turn with a bit more speed, so I increased my lean a touch further and the bike just fell from under me.I am somewhat perplexed about the situation, though. .............It may seem evident, but I would like clarifying a little about the lean angle.
The bike must be leaned to be in balance, just like it must be kept vertical when tracking a straight line.
There is only one possible angle for each combination of speed and radius of turn.
Those two things rule and the lean angle follows.
You go over the same line for a curve: less speed requires less lean angle; more speed requires more lean angle.
You travel at a constant speed: more radius turn (less tight curve) requires less lean angle; less radius turn (more tight curve) requires more lean angle.
When you are leaned, in balance, describing a circle, there is only one way to go faster: opening the throttle more.
As speed increases, the lean angle will increase in order for the bike to remain in balance.
If you force a bigger lean angle via countersteering, you can only keep balance if you tighten the turn (reduce the radius).
Otherwise, you just throw the bike out of balance.
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Last weekend I hit the neutral 3 times downshifting my new CBR600RR.........
How do you deal with this? Buy a shift indicator? Always memorize each gear (this is not easy if you miss the reference shift at any time)? Get a power/quick shifter?
It is just normal with a new bike.
Check the ergonomics of the shifting lever, as well as the fully free movement of the external mechanism.
Be assertive when pressing the lever, push firmly all the way after clutching in.
Take a look at this:
http://www.motorcycle.com/how-to/motorcycle-downshifting-techniques
Never downshift while leaning the bike.
Practice throttle blipping in order to match the rpms of engaging gears.
IMHO, feeling the vibrations of the engine via tank-legs and the torque via seat-butt is better than any shift indicator or memorization.
Braking
in Cornering and Techniques
Posted
Have you purged air out of the lines and calipers?
Have you cleaned the pistons and pad's pins?
You move the weight of the bike away (off-center) as you shift your weight over: the bike is slightly leaned towards the outside of the upcoming corner and the balance remains.
In order to reduce the force pushing your body forward, you can also use more distance to brake.
The bonus of doing so is that you can better adjust or fine tune the correct entry speed before reaching the turning point.
Your time may suffer a bit, but you will feel more comfortable and will corner better and safer.