racer
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Hi all.
I'd like to post a correction to a part of my scientific exploration of some of the forces involved in hanging off above:
When leaned over cornering on a motorcycle, the force of gravity and the lateral g-force are balanced around a common lever (or moment arm) drawn between the center of mass and the contact patch of the (rear?) tire ...I have done some more reading on moment arms or the "lever" that is worked by gravity and lateral g force when leaned over and ... I think the sentence above applies only when all (or nearly all) of the weight is biased to the rear. If the weight is balanced 50/50 between front and rear, I think the moment arm should be drawn vertically from the center of mass to a spot on the ground between the contact patches.
I'm not really a scientist, I just play one on the web
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... how much more lean angle do I have available ... ?
Look at the unused portion of the tread at the edge of your tires. Some people refer to these as "chicken strips". That should give you an idea.
On the street I'll probably have 1/2" unused.
Riding school or trackday probably about 1/4".
Racing ... 0".
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I have ignored a critical point regarding turn radius vs cornering forces, ie. if hanging off allows you to use less lean angle for the same speed, what happens to the turn radius? Will it remain the same?
http://www.glenbrook.k12.il.us/gbssci/Phys...cles/u6l1e.html
From: Equations for Circular Motion
Fnet = m * V2/R
So, it would seem that, in terms of force, speed and radius are proportional. If the throttle and velocity remain consistent, then radius must also remain consistent.
Hmmm...
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But, in the totally clinical conditions of a 360 degree constant radius track, I would think that one would be locked into a constant speed: the throttle would be very nearly still. I'm guessing that its a "steady state" condition that tests weight bias in isolation, no?
Can you negotiate the same radius turn slow or fast? Is a closed circle not an endless turn?
More speed = more lean for the same radius turn.
(BTW: really diggin' this thread!)
Me too. -
Scientifically speaking:
This is my idea of what is happening with the physics of a motorcycle when a rider hangs off. If anyone has a better answer, please speak up.
OK...so...in general, getting your body mass low toward the inside of the corner is the goal. Being 'crossed up' by having body mass (head, torso, etc) up over the bike negates the effect of the mass of the other body parts (hips, butt, leg, etc) that are hung off. In other words, if you are going to be really crossed up, there is no point in hanging off. It won't really accomplish anything.
As for the idea of "getting weight over the bike to put more weight on the tires" ... first, scientifically speaking, we need to separate the concepts of mass and weight. Mass is a measure of matter, weight is an effect due to a force like gravity. On Earth, 1 kg of mass weighs 2.2 lbs due to gravity. Being that gravity on Earth is constant (at 1g), this relationship is consistent all over the planet, hence, one may express weight in kilograms without confusion ... here on Earth. However, if we travel to the Moon, 1 kg weighs ~ 0.36 lbs as the force of gravity is only 1/6 what it is on Earth (or about 0.166g). So, mass remains consistent regardless of forces applied. Weight does not.
Cornering creates "lateral g force" toward the outside of a turn. The amount of lateral force required to create the same weight going sideways as gravity creates going down is, again, 1g ... 1g of lateral force. Sports cars are often rated for the amount of "lateral g-force" they can create.
When leaned over cornering on a motorcycle, the force of gravity and the lateral g-force are balanced around a common lever (or moment arm) drawn between the center of mass and the contact patch of the (rear?) tire and create "weight" in both directions ... down and sideways. Basically, the angle at which the lateral force (weight) equals the vertical force (weight) is where the bike will balance.
By hanging off, we lower the center of mass for bike/rider which, first, reduces the length of the lever (moment arm) overall and increases stability (it takes more force to move a shorter lever than a long one). More importantly, a CoM offset from the centerline of the bike, or biased toward one side of the bike, leans that CoM/lever away from the balance point (between cornering forces and gravity forces), hence, the bike has to stand up more to remain balanced at that speed, sort of like a counterweight allowing the bike to balance the same cornering force (same speed) with less lean. (Think sidecar monkey.) Or, to turn it around, it allows the bike/rider to balance more cornering force (go faster) than if they didn't hang off at a given lean angle. To say it another way, one can go faster at the same lean angle if they are hanging off than if they aren't. And, hence, they can lean further and go still faster.
Now, what happens if you climb on top of the bike to "add more weight to the tires"? By definition, the bike must then lean over more to remain balanced and tracking on two wheels. So, we can't really consider vertical weight in isolation when shifting mass around on the bike. For every gain here there is a loss there as CoM must reamin balanced wrt gravity and lateral G's.
I have ignored a critical point regarding turn radius vs cornering forces, ie. if hanging off allows you to use less lean angle for the same speed, what happens to the turn radius? Will it remain the same?
Whadya think?
r
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Keith Code teaches students to hang off with the body "long" and low, parallel to the bike, ie. not crossed up over the tank with limbs sticking out. The subject has been discussed here ad infinitum and you can undoubtedly find dedicated threads including posts by Keith and the riding coaches explaining the "why" of it if you use the search feature at the top right of the page.
I think your BP in the first picture looks pretty good according to CSS's program.
I could speculate all day about the reasons why some pros don't do it that way. For instance, I think the specific technique is relatively new (in the last ten years) and many pros undoubtedly trained before Keith started teaching it and simply don't know about it. It was not a part of the curriculum when I trained with the school some years ago. Many racers around the world surely never took the CSS school at all. Or even trained with anyone at all. They are merely doing what comes "naturally" for them. Then there is your point about personal preference, what works for them, etc.
I don't have time to get into the science right now, in the meantime, check out this cool physics course website or one of the many others you can find with a search engine like Google:
http://www.glenbrook.k12.il.us/gbssci/Phys/Class/BBoard.html
racer
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Hi Darryl,
In my experience, there is no such thing as a stupid question. Asking questions is the beginning of all critical thinking and problem solving. I think sometimes the desire to 'not' be wrong (or fear of looking stupid) can cause people to avoid asking questions and get stuck.
Zen quote for the day: Ignorance is the beginning of all learning.
racer
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Hey Darryl,
I'm sorry if my last post was a bit overwhelming and hard to follow. I was thinking out loud off the top of my head (in a hurry) and I didn't have time to trim it down to more 'bite size' pieces. I didn't mean to grill you or express doubt in your perceptions, I was just trying to cover all the bases at once in a single post and probably covering none of them well...lol.
So, let me see if I can do a better job of it here and keep it simple.
If you installed suspension components out of the box the way they were sent to you (from Kyle?) it might still be a good idea to have a local suspension pro go through it with you in person to make sure the settings are a good baseline for you.
And, if the bouncing is only happening in one turn (and nowhere else), I would get really, really clear about what is happening in that one turn before assuming it is a suspension issue.
Hope that helps,
racer
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BTW: Am I right about my weight bias? If my front end is sliding at constant speed and constant radius then I should move my weight back?
That sounds like a good idea to me.
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This turn does have issues with ripples from car braking but I don't think that is the cause.
Why not?
Does this mean that you believe you are avoiding the ripples? Like you have found a smooth line through the braking zone?
Or does it mean you are riding over them but you are familiar with what ripples feel like and what is happening does not feel like that?
Ripples in the pavement from cars can be pronounced or subtle. Sometimes they are more wavy than bumpy washboard. Sometimes there are other imperfections in the pavement that might not be noticed if one is focusing on avoiding the car bumps.
My problem now or has been is that I tend to get into a bounce that I can't get out of from time to time depending on how hard I brake."From time to time" and "depending on how hard you brake."
So, does this mean that it only ever happens when you brake hard in that one corner and that you are able to control it by braking less (and perhaps sooner?) so that the "time to time's" that it doesn't happen is definitely because you are braking less?
To put it another way, are you certain that how hard you brake isn't moving your braking zone over some imperfection in the pavement?
Is turn five the only place this seems to be happening? Can you re-create these oscillations in other turns or in a praking lot?
That being said, the bounce seems to feel like a resonance that begins under hard breaking ...What is the frequency of the resonance? Once per second? 2x/sec? 5x/sec?
It feels like riding down rutted dirt road in your car like it just picks your car up on the top of the ruts and theres not much you can do until you get the car slowed down.OK, to my ear, from everything you have said...unless you are certain that are riding a smooth piece of pavement that does not go over the ripples...it sounds exactly like you are describling riding over the ripples and that the bounce is being caused by them. Owing to the fact that it only happens in one turn and your verbal description "car over ruts" ...ruts dug up by cars sounds like a description of ripples dug up by cars. So, are you sure you might not be riding over the ripples ... from time to time?
Now, if you are riding over ruts (or ripples), and "skipping" over the tops, I would say that decreasing the rebound damping to allow faster rebound and allow the wheel to track better or follow the ruts better might help. And perhaps a touch off compression as well. Assuming you can't find a smooth line first.Picks your car up on the top of the ruts".But...you said that you don't think the ripples are the cause.
So, if you don't think the ripples or pavement are causing the "resonance", I would isolate the situation and attempt to re-create it under some control situation. And as it only seems to be happening in this one corner ...from time to time. Maybe you are connecting it with the hard braking in your mind, and maybe hard braking does coincide with the the "bounce" and is intitiating it, but, maybe the braking itself is not really the root issue. And maybe changing the suspension isn't the answer at all.
Have you asked other riders about their experience in that corner? Did you talk to Dan Kyle about it? You said you trust him, but, it wasn't clear why you mentioned that. Did he tell you to back off the rebound damping?
Anyway, I would get really clear about the conditions, ie walk the track and look closely at the pavement and your RP's and brake markers to know well where you are, where all the bumps are ... and look for a smooth line. Amd ask other riders what they are doing. If you are confident that the suspension was set up to baseline correctly, I would look at that only after being really clear about the one corner that seems to be giving you trouble as the suspension seems to work fine everywhere else?
I mean...why only turn five? And why potentially sacrifice good operation in ten other corners to solve a situation in one?
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Forgive me for replying off-topic here, I have no idea what the answer to your question is. I just couldn't resist asking about your job. I've always found the idea of offshore drilling intriguing, ie hi-tech, big machines, out in the middle of the ocean, etc. Anyway... I just assumed offshore oil platforms would be manned by more or less 'local' talent, ie guys working rigs in the Gulf of Mexico would be from or live near the coast of Texas or Louisiana, or somewhere they could conveniently hop a boat or helo. It never occured to me that someone who lives in the middle of the continental US, a thousand miles from the nearest ocean, would work on an offshore drilling platform ... much less a rig off the coast of Brazil!
Sorry for being so nosey. If you don't mind my asking ... what sort of job do you do and how did you get there?
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Can you describe what the "bouncing" feels like in a little more detail?
I am not really familiar with this particular corner but I get the idea the 'bouncing' or oscillation begins in a downhill braking zone and that you aren't hard on the brakes?
I don't like to give suggestions without knowing more detail but my initial instinct would be to *increase* damping, maybe both rebound and compression. Without more info it is hard to say for sure. But assuming springs, oil weight and oil level are correct, that is where I would start. I don't know what the rebound range is; but, for a rough sort I'd give it more than just 1-2 clicks. I'd try 3-4 to see if I were going in the right direction. Once I knew which way to go, then I'd fine tune it.
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Maybe in Randy's mind being 'of the gas' is like being one with the gas...
Good point. I didn't think of that. I just assumed it was a typo for "off the gas" from the context of his statement that the front turned in quickly combined with the inserts comment which led me to think he was turning in and "tucked" the front. But...he isn't really perfectly clear about that.Or a typo, should have been 'on the gas'. -
Google Earth says there is about 70 feet of elevation change from the highest point to the lowest point.
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Eee-yup.
That sentence caught my eye, too, Adam. Good point.
That said, however, I don't know what kind of turn it is and he didn't say what part of the turn he was in, ie. turn entry, mid-corner, etc.
I wonder what they did with the off-set insert in the gooseneck? More aggressive with the rake perhaps? Gives quick response but is less stable...?
It is hard to imagine that someone at his level wouldn't have a good handle on the basics, but ... ?
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I was trying to post a link to Google Earth. Never tried it before. I got sidetracked trying to figure out how to edit that jumble of code and then treying to figure out how to post the link last night and forgot all about your question in the process.
I've never ridden either 'Big' Willow or Streets, but, your description sounded more like what I've heard said about the big Willow track.
I suggest that you download Google Earth (free) if you don't have it already and go find Willow Springs. It will give you a decent idea of elevations and such.
Cheers.
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:shocked:
Er...why can't I edit my last post?
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Ambient temp and track temp will affect tire temp and pressure. Tire reps at the track will usually post recommended "cold" starting pressures to achieve optimum 'race' temp, ie. lower pressures on cold days will allow more flex in the tire and help achieve more relative rise in temp to reach the optimum temp for the compound. For instance, a typical recommended cold starting pressure might 32 psi on a hot day, 30 psi on a warm day and 28 psi on a cold day. A wet track means slower speeds, hence, less flex. Also, the water will cool the tire as well. Once "cold" pressure is set, you should not need to adjust it over the course of a day or really even a race weekend unless the tire is leaking. However, you should check your tire pressure in the morning and before and after every session to record and for safety.
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As for the Valentino quote it is translated as folows:" A motorcycle is like a dangerous women". Take care and hope to hear from you soon.
Two n's. Donna. Doh.
No wonder it didn't make sense to my ear. Must be the blue type in the tagline being so hard to see.
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Hi Macky
2 hours away, that's not bad to get to a track, most in the US are further than that...
Right?
Two hours? That's like two whole hours?
Must be nice! LOL!
The average drive for me is 8-12 hours in a single region. Forget about driving 2-3 days to get to Daytona or Laguna.
That said, with Beaver Run open now, there are now two tracks within two hours of Pittsburgh.
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are groups B and C pretty fun??
Um... speaking for myself... I've never raced a class that wasn't fun.
Although there was one funky WERA GT or something that allowed vintage 250's with modern 125's and FZR400's... bloody old 250's park in the corners and motor past on the straights. Really annoying.
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Hi Steven,
I can't give you any better firsthand info than you already have re: racetech products. I can say that a cartridge fork system is superior in general. In the past, stock shock units were inherently inferior to aftermarkedt dedicated race shocks (particularly for track riding and fine tuning for the track), but, I am not familiar with your model or the current state of the art for OEM suspensions in general these days. And even riding an advanced class track day, I can't say that your stock unit would necessarily be holding you back. Someone else might have a better answer.
That said, I'm curious about the Valentino Rossi quote in your tagline. My Italian is a bit shaky to say the least, and a word for word literal translation doesn't quite make sense to my ear, so I'm wondering if this use of come would best be phrase translated (loosely) along the lines of:
"A motorcycle is only as risky as you make it" or "... is as much a risk as one brings to it (or 'gives' to it)" or something like that?
In other words... a motorcycle is just a motorcycle. It is the rider who is risky or "a danger".
Thanks,
racer
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Hi super60,
I assume you are posting this under "School Questions" hoping for an instructor to reply. I am not one; but, while you wait, I can offer my own perception of my riding...
For me, step 5 (of your list) seems to take me all the way to the first half of step 8 in about 1/2 second...or maybe even less. And it seems that when I stop putting pressure on the bars, the bike stops changing lean angle. My upper body generally does not move (that I am aware of) during that short time frame.
In any case, # 9 in your list would seem to suggest an answer to me.
My humble advice, based on your description and my own experience, is to complete step 6 prior to step 5 and to stop adding step 7 and part two of step 8 altogether. And, of course, to smoothly get back on the throttle as soon as possible after you reach the desired lean angle.
Why are you moving your body back and forth while leaning in?
racer
Me too.
Trail Braking---not That Fastest Way, But They All Do It
in Cornering and Techniques
Posted
Interesting. So if the "brake meter" is merely displaying negative forward acceleration, it may be indicating "braking" when, in fact, the rider is merely "slowing" due to being off the gas. Huh.