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Body Position - Help (pics)


avih

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racer, yes, I've read the Twist Of The Wrist books (1 & 2). The CBR is 2K4 I think (previously a Ten Kate SBK bike) and the tank is quite wide, at least wider than other bikes I've ridden. It's not my bike and the feedback I was hoping for was more general (which I got plenty of thus far, thank you).

 

Regarding weighting the pegs, I didn't intend to start an off topic discussion and I mostly agree with you. I don't try to put specific weight on either peg, but I did notice that I put more weight on the inner peg while inside a turn and that putting weight on the inner peg during steering action makes the steering faster.

 

I can also try the calf raise (mistakenly referred to by me as "California raise") which I don't currently practice. I had the impression it is used for locking the leg onto the tank, and since I feel pretty planted and comfortable as is, and I saw that many (most?) pro riders use similar foot position to mine, I didn't feel a need to try it. It would indeed require stompgrip or a similar product as my tank also doesn't have a sticking tank edge.

 

hubbard_28, I'm at the back of the seat, as far as I can tell, but I can check it out again next time. In this regard, the CBR's seat is shorter than my bike's (GSXR1000 2K4), so the freedom to move backwards is somewhat limited.

 

So if I try to summarize the tips so far, here they are:

 

- Move further back on the seat, if possible

- Hang off more

- Lower upper body and head, towards the mirror

- Try the calf raise to see if it makes a difference

- Go faster, lower ;)

 

Right?

 

Thanks again for the help so far, your feedback is valuable for me. Don't stop with the tips if you have more ;)

 

 

Hi

I am also tall (6ft 1) and find it can be a bit awkward getting a good bp, I dont get my knee down but have pics where I am really close, this is not really a goal I focus on! Something I practice to get my head and body lower on the bike is aim to rest my nipple on the fuel filler cap, if that makes sense, left nipple turning right, right nipple turning left and aim to be looking out side of the screen, not over the top of it!

If you want to increase flexibility try www.netfit.co.uk for a massive list of streching exercises you can try!

 

B

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"I try to keep my weight evenly distributed between both pegs. Like I'm standing on the pegs crouching down low. I'm told that weighting the inside peg can help intiate a slide. Or that weighting the outsde peg can help control a slide. "

 

 

 

Racer, I have never understood the weighting the pegs thing. My weight is on the inside peg because the vast majority of my mass is over my inside peg. I have no ability to weight my outside peg if my mass is over my inside peg. So, for my understanding of physics, if you are hanging off to one side you can not have both pegs equally weighted. It just doesn't balance.

 

Is there something I am missing? I have heard some very skilled riders talking about weighting a certain peg, but I don't see how it can be a function of anything but body position -- mass distribution and the reaction points. Putting your knee into the tank will only reduce your overturning moment (since I have seen you use the term moment), this further reduces the amount of weight you can put on the outside peg.

 

I do not want you to confuse this with arguing with you, because I am not. I just do not understand how it could be physically possible.

 

It's a matter of angular acceleration and centripetal force.

 

Ride faster. :P

 

 

It wouldn't appear that you could generate enough centripetal acceleration of the bike and rider about the turning radius to create any significant angular acceleration about the CG (fore/aft axis) to be able to alter your reaction at your outside peg. The overall force in a turn should be very close to the mid-plane of the bike. So the centripetal acceleration (or force if you like) is offsetting the acceleration of gravity...and hence you have a lean angle that is at equilibrium.

 

"It wouldn't appear..."?

 

What does that mean?

 

The fulcrum of the moment arm (if you will) that is the motorcycle is effectively defined by the contact patch(es) of the tires because the motorcycle is essentially a rigid body with no choice in the matter. The limit of that relationship is defined by available traction.

 

What defines your moment arm? Are you a rigid body? Do you have a choice?

 

 

For the record, my point was that I don't attempt to push on one peg or actively "weight" one peg more than another. That statement speaks to my efforts. Whether that means my "weight" (if you prefer) is perfectly balanced between the two pegs is another matter I suppose.

 

 

Racer, for the record I am a contracting Aeronautical Engineer (a stress analyst to be exact) and I use terms like "appear" to be nice and tell you that you are incorrect. I am often confused by your perception of physics. I had noticed you finally started using centripetal after you wrongly corrected someone else for using it. Not understanding centripetal acceleration lets me know you really have no clue about engineering and by using little terms like "moment" you intentionally try to misrepresent yourself.

 

To come back and attack me when I was trying to nicely get you to look at your freebody diagram, is rather irritating.

 

There is no resultant moment, that is why the mass (you and the bike) don't flip over because there is nothing to resist the moment. The tires are pinned (can't support a moment) and there is nothing else external to the mass that can resist a moment.

 

Where exactly is your reactionary moment? Sit in the middle of the seat....take your feet off the pegs....turn the bike....where is the force? Right down through the midline of the bike! If you move to the inside (with your feet now on the pegs), the inside peg must increase its reactionary force and the outside peg must decrease its reactionary force.

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It wouldn't appear that you could generate enough centripetal acceleration of the bike and rider about the turning radius to create any significant angular acceleration about the CG (fore/aft axis) to be able to alter your reaction at your outside peg. The overall force in a turn should be very close to the mid-plane of the bike. So the centripetal acceleration (or force if you like) is offsetting the acceleration of gravity...and hence you have a lean angle that is at equilibrium.

 

When you hang off, the CoG is off-set from the mid-plane of the bike. As I understand it, the overall downward force follows the CoG. Hence, why the bike follows the same line when hanging-off/standing up more. So, the down force does not change. It remains where it was. With the bike more upright this should give the angle of force from your body an "overturning moment" around the z-axis (longitudinal).

 

In any case, one way to get off the inside peg is to lock onto the tank with your outer leg.

 

 

Yes, when you hang off, it moves the CG to the inside. And yes the resultant force (including moments) all act through the CG of a body (body here means combined mass). No, the downforce can not change in a straight line (line meaning vector) unless you eat a lot of Big Mac's on the way down the straight. The only way the resultant downforce (down to the bike, not to the earth) can change is by changing the direction of the bike.

 

The bike's lean angle is at equilibrium once you make your initial flick and hold it. So, the bike isn't rotating about the longitudinal axis. You don't need to do anything to keep the bike turning, once it is turned. And, the farther the riders body is to the inside, the less weight is on the outside peg.

 

Yes, as I stated putting your knee into the tank will only lessen the force on the outside peg. I need to know how you ADD force to the outside peg.

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I've tried to offer some insight from my point of view, but, you seem to be stuck in a box of your own making. And trying to drag others in with you while not answering or even considering the questions or ideas I've pointed you toward.

 

As I said up front in my original reply to avih, (like you) I've heard other people talk about favoring one footpeg or another. I've never done it. I have no experience with it. I really have no interest in it. Not sure why you are apparently so obsessed with it. Or obsessed with proving it is impossible. But, if you want to know what somebody else meant, I suggest you ask them.

 

At the risk of repeating myself, again, I think it has more to do with the choices and actions riders make with their flexible bodies and muscles, as opposed to moments or combined CoG or whatever else one sees in a static snapshot analysis of a freebody diagram. Perhaps it has less to do with conditions and more to do with what the rider is doing. The rider is not a static free body diagram. And neither is the bike. There is more than one lean angle, eh?

 

That's my best guess.

 

Good luck with your quest.

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It wouldn't appear that you could generate enough centripetal acceleration of the bike and rider about the turning radius to create any significant angular acceleration about the CG (fore/aft axis) to be able to alter your reaction at your outside peg. The overall force in a turn should be very close to the mid-plane of the bike. So the centripetal acceleration (or force if you like) is offsetting the acceleration of gravity...and hence you have a lean angle that is at equilibrium.

 

When you hang off, the CoG is off-set from the mid-plane of the bike. As I understand it, the overall downward force follows the CoG. Hence, why the bike follows the same line when hanging-off/standing up more. So, the down force does not change. It remains where it was. With the bike more upright this should give the angle of force from your body an "overturning moment" around the z-axis (longitudinal).

 

In any case, one way to get off the inside peg is to lock onto the tank with your outer leg.

 

 

Yes, when you hang off, it moves the CG to the inside. And yes the resultant force (including moments) all act through the CG of a body (body here means combined mass). No, the downforce can not change in a straight line (line meaning vector) unless you eat a lot of Big Mac's on the way down the straight. The only way the resultant downforce (down to the bike, not to the earth) can change is by changing the direction of the bike.

 

The bike's lean angle is at equilibrium once you make your initial flick and hold it. So, the bike isn't rotating about the longitudinal axis. You don't need to do anything to keep the bike turning, once it is turned. And, the farther the riders body is to the inside, the less weight is on the outside peg.

 

Yes, as I stated putting your knee into the tank will only lessen the force on the outside peg. I need to know how you ADD force to the outside peg.

 

You either did not understand what I meant or apparently you didn't hear me. You seem to be repeating yourself while ignoring my replies and questions of clarification that you have edited from the posts you quote here.

 

That said, assuming the rider does not move from whatever position they are in, there are two ways I can think of to add more force to the outside peg. One is to ride faster, the other is to lift the bike to a lesser lean angle.

 

If you want to know what these riders mean, I would start from a position that does not assume what they are saying is impossible. I would try looking for the conditions that do allow what they are saying. Unless you think they are all insane or something?

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If you want to know what these riders mean, I would start from a position that does not assume what they are saying is impossible. I would try looking for the conditions that do allow what they are saying. Unless you think they are all insane or something?

 

 

Racer,

 

I actually really did jump into this thread to find out just what riders meant and how they were weighting their outside peg while hanging off. I just got a bit upset when you attacked me when I was just trying to get you to look at the freebody diagram again.

 

 

 

But, just to clarify we do use static freebodies to represent objects that are moving. That is no stretch whatsoever. That is how we design, optimize and substantiate aircraft.

 

 

I will probably just drop by and read some posts from time to time but try harder to resist posting on this forum. I want to learn, not argue.

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I will probably just drop by and read some posts from time to time but try harder to resist posting on this forum. I want to learn, not argue.

 

Meat,

 

First of all, please don't go away, it's great to see activity and alternate viewpoints on the forum; I totally understand your reaction and sometimes the discussions do go a bit awry, but this is a competitive crowd, it's bound to happen occasionally. I was lurking and not posting, too, for exactly the same reason (I'm an engineer, too, incidentally), but I recently decided to give it another try, and I hope you'll stick around too.

 

Second, you had a question about weighting the outside peg - you made a comment that 'putting your knee into the tank will only lessen the force on the outside peg' - and I see your point, but I also see how it could sound contrary to someone's riding experience - it did to me, at first. Something to keep in mind, is that if you use the calf raise it is possible to lock your knee into the tank and then actually PUSH down on the outside peg with your foot, using your calf strength to do so (and I have to do that, to really lock my knee in tight, plus the higher pressure on the peg helps keep my foot from sliding off the peg). I am not making any statement about how that affects the bike (presumably not at all), just adding the consideration that you can push harder on the outside peg without shifting your weight, which may FEEL like adding weight to the peg. In reading this thread I started thinking about BP and at first I thought I put a lot of weight on that outside peg but then realized I am PUSHING on it, not standing on it. So I am increasing the pressure on the peg (but not the weight) whenever I push my knee into the tank. Does that make sense?

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Second, you had a question about weighting the outside peg - you made a comment that 'putting your knee into the tank will only lessen the force on the outside peg' - and I see your point, but I also see how it could sound contrary to someone's riding experience - it did to me, at first. Something to keep in mind, is that if you use the calf raise it is possible to lock your knee into the tank and then actually PUSH down on the outside peg with your foot, using your calf strength to do so (and I have to do that, to really lock my knee in tight, plus the higher pressure on the peg helps keep my foot from sliding off the peg). I am not making any statement about how that affects the bike (presumably not at all), just adding the consideration that you can push harder on the outside peg without shifting your weight, which may FEEL like adding weight to the peg. In reading this thread I started thinking about BP and at first I thought I put a lot of weight on that outside peg but then realized I am PUSHING on it, not standing on it. So I am increasing the pressure on the peg (but not the weight) whenever I push my knee into the tank. Does that make sense?

 

Yes, completely. Exactly. Precisely.

 

Thank you for putting into plain english what I couldn't.

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Meat,

 

Apparently there is some issue with the server here as several posts were not up when I replied this morning before leaving for work and have since appeared (for me) above where I replied. So, I did not see where you stated your explanation of "it wouldn't appear"... which is total BS. Your entire premise in the post to which I referred remains unfounded and unsupported by any physics theory much less proof. As do your accusations.

 

I have no idea how I have attacked you, or how you are twisting or perceiving my words, or imputing my intentions in your mind to believe I have. However, your attack on me, my character, my intelligence and integrity is pretty straightforward.

 

I can see how you might be feeling a bit sensitive after some other replies to you in another thread where you blatantly and rudely attacked the school, but, please don't take it out on me.

 

That said, IMO, your energy has been particularly negative and disruptive in more than one thread. If you do intend to post more, I for one would ask that you please try to be a bit less nasty, self-centered, egotistical and narcissistic. I would also suggest that you leave the victim card in your pocket. The 'poor me' game doesn't carry much weight around here or anywhere else around the race track. And it certainly doesn't make up for a lack of evidence, explanation or intelligent discourse. Nor do insults and characterizations constitute a valid argument.

 

That is not meant to be an attack. It is intended to be a polite request and sincere advice.

 

Regards,

 

racer

 

PS - For what it's worth, my engineering degree is electrical. Not mechanical. But I eagerly await evidence to support your accusations regarding my understanding of physics or perception of engineering. Please point or link us to the relevant posts or quotes. I am always happy to be wrong. Being wrong is the beginning of all learning.

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racer, pardon me sticking my nose where I maybe shouldn't, but IMHO, it's hard to politely request something from someone while describing his posts as "self-centered, egotistical and narcissistic", and expect him to honor your request or otherwise treat you respectfully. It just wouldn't work. IMO your cynicism doesn't help the situation either.

 

Apparently, we're all engineers here (myself included) and intelligent enough to maintain a civilized discussion.

 

FWIW, I don't consider his posts on this thread as attacks on you or on anyone else, nor in any way inappropriate.

 

It might be a good time now to get back on topic ;)

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It wouldn't appear that you could generate enough centripetal acceleration of the bike and rider about the turning radius to create any significant angular acceleration about the CG (fore/aft axis) to be able to alter your reaction at your outside peg.

 

Could you please explain that in plain english for us blind and uneducated ignorants? Or preferably post some mathematical equations and freebody diagrams to support this premise that just "appears" for you.

 

How much centripetal acceleration would be "enough"? How do you define "enough"?

 

How much angular acceleration about the CG (fore/aft) do you consider to be significant?

 

Do you still believe that angular acceleration about the CG (fore/aft) is the only force that could increase "reaction" at your outside peg?

 

 

I believe these are fair and appropriate questions that go straight to the heart of your premise... and your question.

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racer, pardon me sticking my nose where I maybe shouldn't,

 

FWIW, I don't consider his posts on this thread as attacks on you or on anyone else, nor in any way inappropriate.

 

It might be a good time now to get back on topic ;)

Thank you for your opinion, avih.

 

Are you serious?

 

Racer ... I use terms like "appear" to be nice and tell you that you are incorrect. I am often confused by your perception of physics. I had noticed you finally started using centripetal after you wrongly corrected someone else for using it. Not understanding centripetal acceleration lets me know you really have no clue about engineering and by using little terms like "moment" you intentionally try to misrepresent yourself.

Not that I am actually interested in your opinion of my opinion of Meat's opinion of me.

 

In any case, I think Meat is capable of defending himself, eh?

 

That said, since you brought it up, with all due respect, if you want this thread to get back on topic, you might consider not continuing the discussion in another direction... as you just did. :)

 

Regards,

 

racer

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Great. As far as I can see, the last on-topic post was mine.

 

Whenever you are ready.

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racer, pardon me sticking my nose where I maybe shouldn't, but IMHO, it's hard to politely request something from someone while describing his posts as "self-centered, egotistical and narcissistic", and expect him to honor your request or otherwise treat you respectfully. It just wouldn't work. IMO your cynicism doesn't help the situation either.

 

Apparently, we're all engineers here (myself included) and intelligent enough to maintain a civilized discussion.

 

FWIW, I don't consider his posts on this thread as attacks on you or on anyone else, nor in any way inappropriate.

 

It might be a good time now to get back on topic ;)

 

Gee, I hate to throw fuel on THIS fire, but I have to agree with avih here. Racer, I do think you have been a little hard on Meat (based on this thread only - you reference others that I have not read), and I don't think you can in good conscience really claim that you haven't attacked him at all - for example, I might take being called "nasty" as a compliment, but not everyone would. :) Regardless of who started it, you are certainly capable of being diplomatic enough to calm it down, if you want to. Otherwise, he'll just go away - and is that really the goal?

 

My concern here is that this is a great discussion board and the Superbike School staff are great people, I wouldn't want posters to stop posting or spend hours trying to create a post that is impossible to refute, in order to avoid feeling attacked in the responses. I notice that the posts by CSS staff are always polite, friendly, and encouraging, and I think this is the standard by which we should all judge our responses to those that are brave enough or curious enough to post their questions here.

 

On another note, I think it's pretty damn funny that we have a bunch of engineers here arguing such a complex set of physics problems. My college memories of Dynamics are fading, but didn't we use to always assume a spherical rider and a frictionless track? :)

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While I have enjoyed the discussion in this thread, I feel it has gotten off on tangents at time. I will post some pics and ask for critique on my BP. Three pics from the same turn, unfortunately not the exact same position. One in May, second in June, 3rd just last weekend.

 

MayT4-1.jpg

 

Jun08Tfour.jpg

 

Turn4Ramair.jpg

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Gee, I hate to throw fuel on THIS fire...

 

But you will anyway?

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While I have enjoyed the discussion in this thread, I feel it has gotten off on tangents at time. I will post some pics and ask for critique on my BP. Three pics from the same turn, unfortunately not the exact same position. One in May, second in June, 3rd just last weekend.

 

Hi sleepr,

 

I don't know which photo is the most recent, but, I think the first photo posted looks the best. Your head is lower and further over than in the other shots. And your body is almost parallel. There's room for improvement, but, it doesn't look bad.

 

I think the second and third photos show you sitting up more and a little crossed up.

 

FWIW, forgive me for saying so, and I'm sorry if I am wrong, but, it looks like you might be a bit on the heavy side. It isn't everything, but, physical conditioning and good health do contribute to the package. In any case, I know my beer gut sure gets in my way! :P

 

Thanks for sharing your pic's. Keep up the good work.

 

racer

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Thanks for the comments Racer, you make some good observations, the photos are posted in order and I agree with you on the BP. I've been working to eliminate the ass too far off the seat thing and too lock in better. Old habits die hard though. As for the extra poundage your right on that too! I have managed to lose 20lbs but still have another 30 to go. I think the ass off the seat posture is a result of this as my gut gets in the way of having my shoulders and arms lower. I believe the bad BP may have contributed to a crash I had the wknd of the last photo exiting this same corner. Got it spinning and kept in it so I didn't highside but she finallly came around and lowsided from the rear and slid backwards off the track. I think if I had my ass a little higher in the seat it might have hooked up and drove out better, that being said it was just after a slightly faster rider than me had passed me and I was trying to stay with him. Might have got a little greedy with the throttle! Left a 20 foot darkie followed by 5 skip marks where she came around on me.

 

The hole in the fairing in the last photo is from an impact I had with one of my competitors when he checked up mid corner to downshift. His exhaust ran through the bike and he autographed the left side with his rear tire. Fortunately neither of us went down. Heres a pic of that and my BP in the turn we collided in.

 

_DSC4132copy.jpg

 

Aug10T3preimpact.jpg

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Thanks for the comments Racer, you make some good observations, the photos are posted in order and I agree with you on the BP. I've been working to eliminate the ass too far off the seat thing and too lock in better. Old habits die hard though. As for the extra poundage your right on that too! I have managed to lose 20lbs but still have another 30 to go. I think the ass off the seat posture is a result of this as my gut gets in the way of having my shoulders and arms lower.

I know exactly what you mean. I've lost 25 lbs since April and still have another 30 to go myself. I know how much better you must feel. And how much more difficult it is to ride like that. Congratulations on your success! Now the real work begins, eh? The first twenty lbs were easy. The closer we get to ideal weight the more work it takes to lose it. I may have to give up beer altogether. :( And thanks for taking that observation in the spirit it was offered. It can be a sensitive subject and I was concerned that you might think I was, er... attacking you. :ph34r:

 

 

I believe the bad BP may have contributed to a crash I had the wknd of the last photo exiting this same corner. Got it spinning and kept in it so I didn't highside but she finallly came around and lowsided from the rear and slid backwards off the track. I think if I had my ass a little higher in the seat it might have hooked up and drove out better, that being said it was just after a slightly faster rider than me had passed me and I was trying to stay with him. Might have got a little greedy with the throttle! Left a 20 foot darkie followed by 5 skip marks where she came around on me.

I never do that. :)

 

Seriously though, I don't know if having your butt up higher would have helped or not, but, you did well to save it as much as you did. Did someone tell you that hanging your butt off too much decreases rear traction in that scenario? My initial reaction is to think that having your butt higher would put more weight over the rear. But, I guess the bias might go forward if your torso is off. In any case, it would make you lean over more to maintain the same line. And, accelerating while leaned over, I think more rearward weight bias would overload the rear tire faster. What do you think?

 

 

The hole in the fairing in the last photo is from an impact I had with one of my competitors when he checked up mid corner to downshift. His exhaust ran through the bike and he autographed the left side with his rear tire. Fortunately neither of us went down. Heres a pic of that and my BP in the turn we collided in.

That is a great photo and a better story to go with it. I love things like that. Total impact at speed complete with shattered plastic and tire marks; but, everybody was in too much of a hurry to spare the time to fall down, ha ha! :lol: Excellent! It almost makes you want to leave the damage since it's such a great conversation starter, eh? Too bad your ram air intake is there.

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Hi sleepr (and everyone else),

 

I was unable to attend the races at Mid-Ohio last week due to last minute illnesses at work leaving three department heads out on top of the GM being on vacation. When it rains it pours? Murphy's Law? "Shorthanded" doesn't quite say it. My time off was scheduled weeks in advance, but, there was simply no way I could turn my back.

 

So... I took the opportunity to download the races from Mid-Ohio this afternoon along with the AMA races from Laguna Seca two weeks ago. And, well, I decided to watch, with a technical eye, the front runners, er... front runner, Mat Mladin, as he ran away from the field... specifically for body position as it relates to our discussions here and Keith Code's teachings. In some camera shots I could clearly see Matt in perfect CSS style, head kissing the mirror and body parallel, yet, in other camera shots, he was clearly sitting nearly upright and, well... crossed up. After awhile, I began to notice that the shots where Matt was sitting up were on corner entry prior to the apex and the parallel form was consistently seen exiting the corner!

 

Can anyone say epiphany?

 

It was then that I recalled a thread from this past spring in which Cobie joined in and tried to get me (us) to think about how body position affects weight bias, in general, and, more specifically, during the "hook turn". And in that thread, a CSS student who had recently attended a school remarked in some more detail, expanding the BP description to include the entire corner. Something to the effect of staying high at the corner entry and then dropping down for the exit. That discussion came flooding back as I realized what Matt was doing. (Oh man, I can't wait to get back on track.)

 

That said, my next thought was of you and your photos in this thread, sleepr. And I now have to ask (!) ... can you recall what parts of the corner you are in for each of the photos you posted?

 

Eager for reply,

 

racer

 

 

 

PS - I have to add that I was thoroughly BORED TO DEATH by the AMA races at both Laguna and Mid-Ohio. Very disappointing to say the least. Perhaps it is time for the AMA to go spec on tires. Not that I think that would solve the problem entirely. Unobtainable FACTORY bikes and two sets of rules have a been a fact of life here in the states since I started racing twenty years ago. But, well... let me put it this way... I'm REALLY glad I didn't plunk down the $400 USD it would have cost me to travel to, and lodge at, Mid-Ohio last week. REAL Glad. How sad.

 

(Thank God I also downloaded the WSBK from Great Britain and the BSB from Knock Hill... which are queued up as I write this. BYE!)

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So, regarding your near highside but lowside and butt being up higher...

 

My first thought was that more weight over the rear might prevent the rear from spinning up, and, once spinning, more weight would obviously be a bad thing. But... then I backed up a step and remembered that proper weight bias is about load vs traction and directly proportional to the difference in size of the contact patches, ie. 60/40. Hence, more weight forward should allow harder acceleration (and more weight shift) to achieve the proper 60/40 bias.

 

Conversely, when entering the corner, more weight forward risks overloading the front tire. Hence, if hanging the torso off parallel shifts the weight bias forward as was discussed, high during entry and low under acceleration makes perfect sense... to me.

 

Any thoughts?

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...

 

Any thoughts?

Sounds about right to me :)

On entry you have weight forward due to breaking, so you keep your body backwards. On exit, while the weight shifts backwards due to acceleration, you move your body forward to keep it from wheeling and balance the weight shift.

 

If you shift your weight forward before accelerating, you might not have enough weight on the rear for the traction required for acceleration and you might spin it.

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...

 

Any thoughts?

Sounds about right to me :)

On entry you have weight forward due to breaking, so you keep your body backwards. On exit, while the weight shifts backwards due to acceleration, you move your body forward to keep it from wheeling and balance the weight shift.

 

That's true. But, my point is that there's more to balancing the acceleration phase than merely keeping the front wheel down. The weight needs to be optimized front to rear to "match" the available traction. The relative load capacity of each wheel is directly proportional to the size of its contact patch. The rear contact patch has more available traction/load capacity than the front because it is larger. Hence, the rule of thumb (according to Keith) for "standard" acceleration when leaned over (near the limit of traction) is about 60% weight on the rear and 40% on the front to match the relative difference in size of the contact patches. This rough ratio will give the maximum potential traction.

 

 

If you shift your weight forward before accelerating, you might not have enough weight on the rear for the traction required for acceleration and you might spin it.

 

Right, but, my point is that there is more to the story after we begin to accelerate. After we begin to accelerate, the overall weight bias shifts rearward proportional to the rate of acceleration. So, the more body weight we can shift forward as we accelerate, the more potential for acceleration we gain while maintaining optimum conditions for maximum traction.

 

If we are at say 45/55 (r/f) when we begin to accelerate, some weight shifts rearward. At some discrete rate of acceleration for a given distribution of body weight, we will achieve the optimum 60/40 (r/f) overall bias. If we shift our body position to distribute more body weight forward such that overall bias is altered (back to say 55/45), we must (or can) now increase our rate of acceleration to regain our optimum (or standard) 60/40 ratio for maximum traction.

 

Does this make sense to you?

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It does, to a degree, because the 60/40 rule of thumb applies IMO only when the bike is at it's max lean angle and the acceleration/deceleration is neglectible. In that case, the only force that applies is the centrifugal/pital one which is applied evenly to both wheels, and the weight/traction have to match it. This phase is usually quite short except for very long turns.

 

While breaking, I think we need the bias to the front since that's where the main steering action takes place, therefore, we need as much weight and traction as possible there to steer the bike effectively. The rear traction plays a much smaller role in this phase.

 

On the exit (which is a relatively long process , starting probably just before the apex) when we progressively accelerate, the rear tire needs more traction than the front beyond 40/60, because the rear tire needs the extra traction to support both centrifugal force and acceleration. If we're at 40/60 and at the traction limit and we apply more throttle, the rear will beak loose IMO because it was at the limit already and can't support the extra force from acceleration.

 

In general, the harder the acceleration, the more weight we need on the rear to have the traction needed.

 

On corner exit process, few things happen gradually:

- The turning radius increases

- The bike straightens up

- We apply more acceleration.

 

The front traction is only needed while leaning (and initiating a turn) as it gives nothing on a straight line (I don't count steering correction as relevant for this discussion). Therefore, as we exit the corner, more and more weight should and can move rearwards to support acceleration. As acceleration increases beyond a certain limit where 100% of the weight is on the rear, the body should be forward to prevent the the front from coming up, allowing to accelerate even harder (as long as the tires are good and the asphalt grips well). All these processes are, naturally, gradual.

 

It's all about balancing the traction needs at each phase. On entry we need mostly the front therefore it's probably 80-20 or more biased forward, while leaning we need both so that's the classic 40-60, on exit we need more and more of the rear, ending in 0-100 towards the straight when we only need the acceleration. And all gradually, smoothly and fast ;)

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