Lnewqban
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Posts posted by Lnewqban
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Any theories as to why the rear tyre spins out here..??
What I see:
-Plenty of wet rubber "bearings" on that area from all the dragging car's tires.
-Right foot over rear brake lever (ball of foot should be on peg).
-Steering to the left when the skid started (opposite to proper input to try to save the slide).
-A lucky rider.
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.......Any opinions?
It is just a track day, you are not racing; hence, there is no reason to brake so hard.
http://forums.superb...p?showtopic=310
IMHO it is not a suspension problem, if the rear suspension is fully extending when that happens.
It is just the result of sticky tires and strong front brake.
Basically, you are lifting the rear tire due to excessive braking (excessive deceleration).
Once the friction of the rear patch disappears, the CG wants to move ahead of the front patch and the tail swings side to side following your minute steering inputs.
http://forums.superb...?showtopic=2423
I wouldn't follow the advice of the other site: steering geometry has nothing to do with the problem; hence, leave the height of those forks alone (unless you are experiencing steering problems).
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.......My question is, if we enter a corner by choosing a lower gear, or by gradually roll off, assume that as soon as we open the throttle, the rpm rise 200 rpm and it hits maximum torque of the bike machine. Will it be safe? will the torque knock out the tyre under minimum acceleration or should i say the right way of riding is to drop the rpm further and accelerate slowly out of the corner? This question has float in my mind for a certain time as i'm asking my self i could roll on the throttle a little sooner just to accelerate out of the corner as soon as possible.
Since the rear tire and the crankshaft are solidly connected, opening the throttle will increase the torque delivered by the engine, but the crankshaft will not rise 200 rpm immediately; the rpm's will increase only after the rear tire overcomes the inertia of the bike and increases its speed (acceleration), which will increase the rpms' of the rear tire.
Many riders purposely enter turns with high gear and the engine working on the weakest portion of the torque curve (very low rpms') in order to minimize the chance of loosing grip due to accidental over-torque (due to "being too "greedy" with the throttle at roll-on").
However, that is just a crutch to compensate for poor throttle management.
Again, the throttle is your supplier of torque; learn to manipulate it with micrometric precision, on and off.
The gear you choose only gives your engine more (lower gears) or less (higher gears) leverage over the rear tire.
From Twist of the Wrist II:
"By the numbers, we want to transfer 10 to 20% of the weight rearwards, using the throttle.
Technically, this is 0.1 to 0.2 G of acceleration.
Simply put, it's the force generated by a smooth fifth-gear roll-on in the 4,000 to 6,000 rpm range on pretty much anything over 600 cc.
That's not much acceleration, but it does the job.
It seems riders often have difficulty sorting out this small amount of traction-maintaining-throttle through turns, instead trying for more dramatic acceleration.
This is most easily seen in the common error of being too "greedy" with the throttle at roll-on, which will make the bike run wide or slide and lead to a roll-off."
Note that the book doesn't mention brutal torque or HPs', it refers to fine and sustained input (throttle) from the rider, and consistent output (smooth acceleration and bike-suspension stability).
High lean angles are less forgiving of any errors regarding "being too "greedy" with the throttle at roll-on", simply because all the traction available is dedicated to resist the high lateral forces.
Moderated lean angles will allow certain margin for such errors.
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Very interesting and intense work, Noamkrief !
Checking my daily commute for the "turtle speed" and lean angle of 10 degree, I would be way over the legal speed limit for each of the sections of my trip.
It would be interesting to apply it to tracks.
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......Listening from his explanation, it sounds like he had a slip on this rear tyres, than shut off the throttle and than his front just gave way.....
It didn't have to end up that way:
The available torque translates into additional longitudinal force on the rear tire's contact patch.
The acceleration that the bike is experiencing during a turn is the best thermometer of the magnitude of that additional force.
In order to put invisible forces in perspective:
- The recommended 0.1g ~ 0.2g acceleration (gain of 2.2 ~ 4.4 mph per each second on the turn) is the result of an additional longitudinal force on the rear patch which is equivalent to 10 ~ 20% of the bike-rider combined weight.
- At 45-degree lean angle and under the recommended acceleration, that rear patch will be stressed with a lateral force equivalent to 60% of the bike-rider combined weight.
The above forces combined result in an actual lateral load on the rear patch of 61% ~ 63% of the bike-rider combined weight.
- Heavy braking while upright can stress the front contact patch longitudinally as much as 85 ~ 100% of the bike-rider combined weight.
- During the extreme case of a burn-out, the longitudinal force on the rear patch overcomes the traction of it, which in that case is around 50% of the weight of the bike (the rider usually stands up on the pavement to reduce tire traction).
As Acceleration = Torque / Combined weight, the acceleration that your body feels is proportional to the torque that the rear tire feels.
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Although it takes the same amount of time, it takes a LOT more distance to slow from 100-70 than from 40-10.
It takes three times more distance.
Braking distance = (V final ^2 - V initial ^2) / 2a
It takes 65 m (213 ft) to slow down from 100 to 70 mph at 0.8 G, while it takes 19 m (62 ft) to slow down from 40 to 10 mph.
However, the forces that the pilot, the suspension and the tires feel, the pressure on the brake lever and the time it takes is exactly the same.
Replicating track speeds for practicing consistent braking would be ideal, but parking lots are more easily and frequently available than tracks.
Again, the only thing that the rider feels different is the speed at which he sees things moving.
Watch how Valentino does brake to set entry speed:
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Ok just so I can go back over this and not have to read through the clutter let me see if this is accurate on what needs to be worked on:
- Visual skills on perception of braking distances
- Set braking points at a comfortable distance
- Better manipulation of the brake lever
- Understanding how much pressure to apply and when
I agree; very interesting.
Since braking from 100 to 70 mph is exactly the same than braking from 40 to 10 mph (except for the speed at which we see things moving), you may benefit from regularly practicing braking on an empty street or big parking lot.
The rate of reduction of speed (deceleration), modulation of force on the lever and G forces are exactly the same as long as a reduction of speed in 30 mph happens in the same period of time.
Rather than waiting for the next track day or race, setting cones or other marks and specific speeds for each could help getting familiar with the right way to accomplish the points on your list.
Progress regarding consistency in braking would be easy to log and check, specially if somebody can help you.
Using a similar system, I practice emergency braking for street riding regularly, and my confidence has grown exponentially.
Check this article about braking threshold:
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.......Honestly on this I can't really say and this is why I feel like my braking process is inconsistent, it's not the quick flick, I am not charging the turns, I am using the 2step drill and I have done all of the same corners with the no brakes drill without undershooting my entry speed.
More than inconsistent, your pre-turn braking seems to be consistently excessive.
"There are two primary methods of braking for a corner: straight-up braking, where you complete braking before turn-in, and trail braking, where you stay on the brakes after turning and feather off brake pressure as you near the apex........
Straight-up braking inspires less physical drama, but still demands intense attention from the rider. In some cases, completing the braking act before you turn is more difficult than trail braking to the apex. In this case, the bike's turning arc must be established before the turn is initiated. The ability to predict line, apex and exit is vital. This requires, among other things, superlative visual skills. In addition, quick and accurate steering is a must. The rider must have enormous confidence in front and rear tire grip before flicking the bike into the turn. Coordinating brake release and turn-in steering actions must be spot-on, or the suspension will rebound as the bike is entering the turn. This all requires deft coordination and impeccable timing..........when you consider the judgment and coordination demanded to skillfully execute quick and accurate straight-up braking entries, I'm not convinced trail braking is the more advanced technique. It may be the other way around." - Keith Code
http://www.motorcycl.../#ixzz2GBdUnMtt
The previous statements explain that your style of braking is hard to achieve properly.
Your problem makes you underperform on the safe side.
Could it be that you have crashed before due to under-braking, and some SR is working at sub-conscious level, making you over-brake?
"You could say that the best riders make the best decisions: when to brake, how hard to brake, when and how hard to roll on the throttle, where to turn, etc. Let’s look at the same thing from another angle: A good rider also knows when not to do something.
Here’s an example: A rider enters a corner, and things seem okay as he tips in. As he approaches the middle of the turn, he becomes concerned about his entrance speed and, although he’s not running wide, he gets the idea that he might run wide. He then launches a preemptive strike on the problem that doesn’t exist......
If we look at preemptive strikes as riding problems, we find that what we are really dealing with are riders’ uncertainties. Resolving those uncertainties has been a major part of my job for the last 34 years. A rider goes into a turn, becomes uncertain, and then starts giving the bike all manner of control inputs that he thinks will make him certain and comfortable? I think not. That’s like stabbing at random buttons on a large machine to try and control it.
If we break down terms like certainty and confidence, we find the common denominator of a predictable result. Gaining certainty or confidence is something we do have a solution for, and here’s how it breaks down: 1) Practice one individual skill at a time; 2) While doing so, ride at about 75 percent of your limit; and 3) From there, incrementally increase your pace." - Keith Code
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.........I come up to the corner and apply the brakes, however I slow the bike down too hard too early because my entry speed isn't where I want it so I find myself getting back to the gas to up my speed. Or I find myself neutral throttle holding my speed too long before the corner where I feel like I could have braked much later and stayed on the gas.
Charging a corner (late braking) is not the fastest way to go through it, later turn-in is.
There is no much time lost if the bike coasts a little between off the brakes, late entry and quick flicking (you enter late and quick flick, don't you?).
"If you were to practice one thing in your riding, I'd recommend you become comfortable with slightly later turn-in points. It's common knowledge that you have a better line of sight through any bend from a later turn-in point.
One of the things that keeps riders from practicing this is they're not smooth in their transition; it feels too abrupt. You can become smooth, but overcoming the early turn-in solves many more problems than it creates, so you put up with the not-so-smooth until you gain some confidence in your later entries." - Keith Code
http://www.motorcycl...ing_motorcycle/
One of the advantages of fine tuning the entry speed with lighter braking at the end of the deceleration phase is that the suspension gets a smoother transition of weight from the front to the rear during brake release, which improves overall traction.
You only have your balance (associated to G forces) and vision senses to evaluate and judge entry speed.
I would work on improving vision techniques first and off-the-brakes smoothness later.
Check these additional articles:
http://www.motorcycl...orcycle_riding/
http://www.motorcycl..._smooth_riding/
http://www.motorcycl...blem_of_vision/
http://www.motorcycl..._a_trained_eye/
http://www.motorcycl...ics_code_break/
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Hmmm.......well let me explain what exactly happens, so I am coming off of 4th gear down shifting into 3rd and applying the brakes. I don't just grab a hand full of brake I progressively squeeze the brake lever and then I brake hard.....
It seems that your problem is not accurately estimating the entry speed (for which the No-brakes drill described in the second link of my previous post works great), since you realize that your entry speed is too low.
Your problem seems to be over-estimating the real speed that you carry at the end of your braking phase.
Maybe the deceleration forces fool you on thinking that you are still above the entry speed that you have estimated.
I would reverse the downshifting and braking steps that you have described:
Look far away - hard braking (80% of the speed to be reduced) - downshifting - look far away - light braking (20% of the speed to be reduced).
In that more natural way, more of your attention is liberated to improve your perception of speed and your eyes "see" less speed.
Worse case scenario, you realize that you are still carrying too much speed: just apply some more light trail braking (fine tuning of speed) while you lean the bike.
You can set a RP for start the braking-downshifting phase.
You should not, however, target fix on that or any other RP.
Keeping track of them only with your peripheral view, will help you to feel your actual speed more accurately.
This article will explain it better:
http://forums.superbikeschool.com/index.php?showtopic=978
Deeper braking will make things more difficult for you, in my humble opinion.
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I am loosing a ton of drive during a chicane that I feel I can take at or near WOT? What is the secret to getting the bike to "easily" flick over while under load? I have tried focus on knee to knee and hard countersteer and sometimes even pushing and pulling on the other bar at the same time? I get it over.... it just doesn't feel smooth.
Ideas?
I don't race or ride at your level; so, I don't know enough to properly advise here.
Just talking Physics:
I just want to remark that the only force able to quick roll the bike from one extreme lean to the opposite one is counter-steering.
Flicking more that 400 lb around the contact patches in a fraction of second requires some more "muscle" than gentle input or legs' relocation.
The lack of smooth feel may be a SR, or the stronger resistance of the steering bar at higher speeds (gyroscopic effect), or the modification that the steering geometry suffers at extreme lean angles (front contact patch is at a weird position and has strange leverage over the bar), or the front suspension working at its worse angle, or maybe a combination of all those.
Turning the bar to tight the turn more (to turn-in more) when you body feels so close to the ground must seem crazy; however, is the only way to make the centrifugal force work for you and stand up the bike with authority.
Keeping that counter-steer input for ~90 degrees or so roll until the bike reaches the opposite lean angle must feel crazy as well.
Then, the counter-steering must be quickly reversed (momentarily reversing the centrifugal force) in order to stop that long-lasting roll at the exact angle that the second part of the chicane requires.
I am not sure, but I believe that having the bike under acceleration during that process is less than ideal.
The reason is that a good portion of the traction of the front contact patch is dedicated to resist the lateral forces of the extreme lean angles (first turn first and second turn later), and the counter-steering inputs for flicking the bike use some traction (more for more energetic counter-steering or quick flick).
It seems to me that acceleration lightens the front contact patch and decreases its traction capability (easier for counter-steering to overwhelm it).
(Don't trust me in this one, I have been wrong before).
Merry Christmas to all !
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Deeper points may worsen your braking inconsistency, since you will have less error margin (regarding space and time).
The proper technique is to reduce a gross amount of speed first (harder braking) and to fine tune the entry speed later (lighter braking).
Maybe simultaneous downshifting disturbs your action on the front brake lever?
These articles may help you pinpoint your difficulty:
http://forums.superb...p?showtopic=258
http://forums.superb...p?showtopic=310
Some time ago, I started this related thread and received priceless advice from other members:
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.......
On the other hand - during chicanes or turn that leads onto another turn in the opposite direction, I definitely haven't figured out how to flick the bike to the other side without using my arms. I can definitely feel unwanted steering input there... On rare occasions I'm able to flick the bike the other way without steering input, but it's mostly luck. I understand the concept of using the legs to switch positions, but haven't applied it in real life yet...
Counter-steering is the only way to flick the bike to the opposite side; hence, you must use your arms.
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Previous post edited to correct the statement:
"That flexibility reduces the total moment of inertia because the smaller mass of the bike can rotate around its CG with certain margin of freedom respect to the mass of the rider."
For the mass of the rider's body not to affect the system's moment of inertia much, the hands, ankles, knees and hips should try to rotate the rider's CG much less than the bike's CG.
This video shows two bodies with similar mass, but different mass distribution, rotating at different speeds under the same force:
An off-road rider stands on the pegs to speed up the nose-up / nose-down rotations of the bike (pitch rotation around the bike's CG), almost completely liberating the bike+rider system of the rotational inertia of the rider (CG of the rider doesn't rotate much thanks to the pivot created by the ankles).
The system becomes "lighter to rotation", which allows the tires to better follow the great changes on the ground or track surface.
That is why trial bikes have the shape they have:
For a bike that weights three times the weight of the rider, if the rider lifts his CG (about where his belly button is) 3" above the original location, the combined or system's total CG will only move 1 " higher than its original location.
Relocating the rider's CG sideways via the hang-off technique has a more pronounced effect on the lean angle that the bike needs to take (lean angle of the system (bike+rider) remains the same to balance the lateral and vertical forces induced by the turn).
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So does standing on the pegs lower or raise the COG???
Fajita,
As Noamkrief properly explains above, standing on the pegs doesn't do much for the vertical location of the CG of the bike+rider system, especially for light riders and heavy bikes.
Where the weight of the rider is supported by the bike is related to internal forces of that system, which don't change the distribution of masses (the center of mass or CG of the whole system remains around the same point in the space).
I don't know calculus but I try to have a good basic understanding of physics.
In order to understand the physics behind the dynamic changes that happen when we stand on the footpegs, one needs to understand the concept of "moment of inertia".
"In classic mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a property of a distribution of mass in space that measures its resistance to rotational acceleration about an axis...........and is the rotational analogue to mass. Mass moments of inertia have units of dimension mass × length2.
The moment of the inertia force on a particle around an axis multiplies the mass of the particle by the square of its distance to the axis, and forms a parameter called the moment of inertia.
The moments of inertia of individual particles sum to define the moment of inertia of a body rotating about an axis."
http://en.wikipedia....ment_of_inertia
http://en.wikipedia....ents_of_inertia
So what kind of effect do you think weighting or standing on the pegs has?
The concept of moment of inertia sounds difficult, but it is not so much.
The bike+rider system always rotates around the combined or system's CG, either during hard braking-acceleration or during quick flicking.
Sitting on the bike, our body has a somehow rigid connection with the bike and; hence, there is one moment of inertia, which has a high value (the system has more inertia to be rotated).
Standing on the pegs, our body has a flexible connection with the bike (via our legs, knees and hips); hence, there are two masses connected by a flexible link.
That flexibility reduces the total moment of inertia because the smaller mass of the bike can rotate around its CG with certain margin of freedom respect to the mass of the rider.
Note that the value of the moment of inertia depends on the value of the mass, but also depends on the square of the distance that separates the CG and the pivot around which it rotates.
Standing on the pegs drastically reduces the moment of inertia or rotational inertia to flicking the bike or to perform a wheelie.
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My good friends that were with me were really excited!!! They couldn't believe the speeds I was carrying (for being new).
And that increased speed and confidence bring a new challenge to you: to learn efficient emergency stop for street riding.
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My question is simple, If i'm in a turn and I lean more (body and bike) what will happen? I feel like if I lean more, the bike will "give up" and fall down - lowside.
Once in a while i'm in a turn and I feel like I need to tighten just a tad bit more. I stay on maintenance throttle and countersteer to lean just a little extra. That little extra lean ads tons more cornering force, The bike dives in to the inside and I feel like there is no possible way these tires are going to stay sticking to the ground.
Watching your video, it is evident that you just need more riding hours.
Your barrier is mental, since you have not learned the new gravitational field in which you ride.
That field is sometimes vertical, like the natural one; however, it is sometimes diagonal.
It is important that you understand that you don't lean the bike in an arbitrary way: you simply keep your bike and your body perfectly aligned with a diagonal gravitational field.
Hence, neither your bike or your body can fall in, if speed and turning radius are in balance.
If either one of those change, your lean angle will adapt naturally (unless you interfere).
If properly inflated, your tires can resist a lateral force as high as the share for that tire of the combined weight of your bike and body (which will happen around 45 degrees of lean).
At 35 degrees, you are not using a big margin of grip (lateral force is only 70% of total weight).
As explained by Hotfoot, that is all the lateral force that your rubber can develop, and riding mistakes can very well overload the tire with more lateral load (example: mid-corner steering corrections) or with additional longitudinal load (example: acceleration or off-throttle).
Extreme lean angle per se does not induce quicker riding.
To be fast, a rider needs to be smooth; to be smooth, a rider needs to be focused and relaxed.
Work on those things and try to forget about the lean angle: it will improve by itself and as you mature as a rider.
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Areas I would like to have a better feel for how much traction I have in either front or rear tire(how close am I to the limit):
Corner Entry on the brakes (Front tire)
Mid corner( front tire)
Mid corner initial throttle applied (rear tire)
Corner exit rolling on more throttle( rear tire)
Currently I'm too 'scared' to run deep into corners with the front brake because I can't feel when the front is going to let go.
I have had two crashes on the track which were carbon copies of each other just turning different directions. Both were sharp >90 degree corners in 1st gear........
Cryo,
Have you studied Keith Code books and DVD?
Your questions suggest that you have not.
It is natural that you are concerned about the interface rubber-pavement; however, there is much more about properly riding a motorcycle, either street or track, which requires careful study and abundant practice.
Read this article:
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........We see some riders backing it in and others not. ......
Rossi is not:
http://www.youtube.com/watch?feature=player_embedded&v=SPLKCNiFlAY
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... So if I start with a maximum lean angle initial turn in, and I accelerate - won't I have to increase lean angle to maintain the same radius turn? If it's a constant radius turn - that could pose a problem.
If we take this one step further - a 360 degree turn non stop round and round - how can we possibly accelerate at the recommended .1-.2 G's? Eventually, we will go too fast to stay in the turn...
Your logic is correct.
However, the recommended 0.1 ~ 0.2 g acceleration to balance the load on the contact patches only adds 3.22 ~ 6.44 ft/s (2.2 ~ 4.4 mph) of speed for each second spent on the turn.
Hence, the entry-out speed difference will be smaller for high speeds, precisely the conditions that generate higher skidding forces (lateral g's) and therefore, require better balance of tire's loads and better suspension's ranges.
For slower or higher radius turns, lean angles (skidding forces) will be less dramatic; hence, the acceleration may well be less than recommended in order to make the entry-out speed difference less dramatic (due to the increased time that the turn will take).
Example: In MotoGymkhana practices, going around cones a couple of turns (~700 degrees rotation / ~5 seconds) with the steering bar against its lock, we don't accelerate at all.
..........I've read alot online about why the rear tire is wider. Most common answer - because it needs to accelerate the bike.
That doesn't make much sense to me - because braking force on a motorcycle or car is much greater than acceleration force, so with that reasoning, the front tire should be wider....
You are correct, acceleration is not the reason.
A stoppie proves that the front tire can handle deceleration (more than 1 g) and full weight of bike+rider.
I believe that the reason is gyroscopic effect (or angular momentum), which helps in the rear for the reasons that you explained above.
For quick turns at high speeds, minimum gyroscopic effect on the front is desirable.
Even during a wheelie, inadvertently steering a strong gyroscope in the air would upset the balance of the bike.
Consider that gyroscopic effect decreases/increases directly with the mass of the tire, and is proportional to the square of the angular velocity (or speed of the bike).
http://en.wikipedia.org/wiki/Gyroscope
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Hi everyone. I'm a new rider - 3 month but an experienced Spec E30 (Infineon / Thunderhill) driver and I absolutely love understanding the physics that control cars, and now motorcycles.
Noam,
Welcome to the site.
I also love the physics behind moving things (dynamics).
Read also this:
The 1g Club - by Keith Code
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What a piece of ###### racetrack.
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It is beyond my knowledge to refute or judge any of these claims. And with a wealth of mis-information on the web I won't be using Google to answer the question. Can any of the coaches or engineers comment on the claims above?
I agree that it is as difficult to understand how all the forces act as it is to explain it.
The posters of your forum are correct regarding the description of the internal forces that involve the chain, sprockets and swing-arm.
However, they fail about quantifying those forces, which are not as strong to make the pivot of the swing-arm sink toward the road as they believe (mainly due to lever lengths).
The external forces and related levers are greater than those internal forces, resulting in that pivot to move up from the road, simultaneously with the steering column.
As a matter of fact, the second rises up at a higher rate than the first, pitching the nose of the bike up, which could be confused with a rear squat down.
Those external forces are generated by the forward acceleration of the combined center of gravity of the bike-biker plus the rotational inertia of the rear tire.
Exactly the opposite things happen during deceleration (braking): both forces act on the swing's arm pivot, the external forces win again, the pivot is pushed down, and the rear of the bike squats (even if clutch is in and there is no tension on the chain).
If our motorcycle were powered by an electric motor directly coupled to the rear wheel's axis (no chain or belt drive), it would be a flywheel hanging at the free end of a pendulum.
If we accelerate the motor, the end of the pendulum (where the wheel is) moves from the vertical in one direction and remains there as long as the acceleration is happening.
If we decelerate the motor, the end of the pendulum (where the wheel is) moves from the vertical in the opposite direction and remains there as long as the deceleration is happening.
If torque is lever times force, a lever (the swingarm) and a torque (the angular acceleration/deceleration or angular impulse of the wheel) generates a force (on the pivot).
Have you ever wondered why the A-shape frame of the Ferris wheels?
When the huge wheel starts or stops rotating (accelerates or decelerates), huge forces parallel to the ground appear.
This video shows an application of that principle (skip to 1:40):
Although the force that is explained above or the torques applied to the swingarm are not mentioned in this article, it is great the way it explains how the remaining forces work:
http://www.sportride...ction_geometry/
Code's stuff is nor simplistic neither incorrect, it is simply a description of reality.
He/she, who has been riding long enough, knows from feeling them, that these things happen this way.
Favorite Keith Code Quotes Or Articles?
in Cornering and Techniques
Posted
Copied from "Embracing the Mysterious Limits of Riding"
http://www.motorcycl...mits_of_riding/
"Making leaps of faith into the unknown by hoping the bike will do your biding often finds riders biting off more than they can chew." - Keith Code