avih

Noticed that factor myself too. My solution though is to "turn" the helmet upwards (as if it rotates on an axis that goes between your ears). Your chin might stick out more than usual but it does the trick when you put your head down. From a safety perspective, I initially thought it would be less safe since you can hit your chin during a crash, but on 2nd thought, it would take quite a coincidence for that to happen. You will have to be flat out on your belly on the track, while your head is backwards for your chin to hit the track. Also, I think I saw Pedrosa using the same "trick"...

In mid turn, the tire that lose traction 1st is the one which has more centrifugal force to hold than traction available by load+CP size (that's not a direct algebraic sum but rather a combination of both parameters) . The theory is that the optimal balance is about 60% on the rear and about 40% on the front such that lean angle and (momentary) cornering speed is maximized. To achieve this balance you usually have to apply a little throttle while turning. If you apply some more throttle then more weight goes backwards, let's say to a balance of 25-75, at which case your optimal cornering speed is compromised. If you try to stick to optimal cornering speed though, the rear will lose traction because it'll have to provide more traction than it can (75% of the bike's weight instead of it's maximum 60% for maximum overall centrifugal force), while the front will hold less than what it can, so the front will not wash out. Imagine a wheelie while exiting a turn. The bike is still somewhat turning, 0% weight is on the front yet the front doesn't wash out (and the rear also doesn't wash out because the centrifugal force is lower than in mid corner and so it can hold). Generally speaking, while at maximum lean/cornering speed, the tire that will lose traction is the one which you request to hold more than it can (40% weight for the front, 60 for the rear). If you apply more throttle then it's the rear (usually high side), if you close the throttle or apply some brake, it's the front (low side). The reason people trail brake is not to keep the weight on the front during maximum lean, but rather to brake later than otherwise and to keep the weight on the front while applying the turning command (which requires much traction from the front). As long as the turning has not started, optimally 100% of the weight is on the front while braking. While during the turn, the front holds only 40%, which leaves the rider to handle the transition from 100-0 in a straight line to 40-60 balance at the apex. Optimally, and taking the turning command into account, this is achieved using trail braking.

Hi, After my previous discussion here http://forums.superbikeschool.com/index.php?showtopic=1098 , I figured two things about my body position: - My abdomen is facing straight forward, while in most pics of pro racers it's directed somewhat towards the bike itself (body is a bit twisted). - My inner ankle is too bent instead of "open", and it carries most of my body weight. It both limits me and not very comfortable. I'm trying to use calf raise, but I still somehow put much of my weight on the inner peg. Also, when I try to take my body out a bit more, I'm losing the calf raise lock of the outer leg and put even more weight on the inner peg. I'm opening a new thread here because my question is very specific and different than my general previous post: While you hang off the bike, how is your body weight distributed? i.e. what points of contact would be the hardest to "take apart"? Do you put much weight on the arm resting on the fuel tank? do you feel much weight on the inner peg (i.e. can you take it off the peg relatively easy and still keep the BP)? do you try to put most of the weight on the outer leg? maybe the thigh on the seat? etc. I figure the handlebars carry as little as no weight at all. I'm guessing this subject has been mentioned, but I couldn't find relevant posts. If someone would be able to point me to some, I'd appreciate it, if not, answers are welcome here too thx

That's why I said accelerate slowly. Let's say, 1MPH more on each lap. For the sake of the weight balance, the acceleration is negligible and therefore we're very close to 50-50 at a constant speed. This ratio prevents us from utilizing the full centrifugal traction potential of the bike (more weight on the front than the optimal balance), hence, we will lose the front before we reach max possible lean angle.

Ahh.. new term is coined, neglectible Indeed, I have not estimated this "40-60 acceleration" in practical terms. It could be interesting, I'll put some time into it a bit later, and try to put it into more accessible terms of percentages/lean angle/etc. IIRC, in TOTW2 there's an estimation of this amount of acceleration in a straight line. BTW , Interesting corollaries of this conclusion are: - By riding round a fixed circle at a constant radius while very slowly increasing speed, you cannot reach maximum lean angle, since as you get close to it, the 50-50 (appx) weight balance of fixed radius/speed with no acceleration prevents you from taking advantage of the maximum centrifugal traction the bike can offer. You will lose the front 1st because it would have higher centrifugal load than it can bare, while the rear will keep tracking perfectly. - If cornering without accelerating, you're at risk of losing the front, especially if you're close to the max lean angle. Even more so if you shut the throttle off or even just ease it while turning. If indeed this conclusion and corollaries are of non-negligible proportions, then this theory of maximum traction availability only in an ever widening arc goes very nicely with late apexing.

Take your time racer, though If I were you, I'd get right on with this post.... There's no need to try and contradict every single sentence of mine, you can do that in a general manner

Thank you racer for your detailed respond, and for the time you took to relate to my post. For the record, I don't find this post of yours offending in any way so I think we can put this issue behind now. Your vast experience and that of other users of this forum is exactly the reason I'm here: to learn, And learned I have. As you, I also like a good discussion. In contrast to you though, my experience is very limited (probably not more than 5 track days overall, some in a limited form) so I try to combine my little experience with logical analysis of situations, and theoretical (for me) knowledge from TOTW books and other sources. Therefore, when I say IMO, it means just that, and its definitely open for criticism and discussion as far as I'm concerned. The same goes for this entire post. I also apologize for my typos and possibly for my syntax errors. I'm not a native English speaker, nor do I speak it daily. I believe negligible is the "passive" form (?) of neglect but my spell checker couldn't fix "neglictible" properly so I left it as is. You interpreted it correctly as I've expected. As for "breaking", oops anyway, thx for your corrections, keep them coming. Before I respond to your comments, let me clarify myself about some terms I've used, just to make the discussion clearer. Please correct me if I'm not precise. - Weight balance of the bike is not body position. Weight balance as I referred to it is the ratio of the vertical force-interaction between front-wheel-to-ground and rear-wheel-to-ground. If the front wheel is off the ground then I refer to it as 0/100 weight ratio (100% of the weight is on the rear wheel). If the rear is off the ground, then I refer to it as 100/0. When I refer to balance in the form of X/Y, I put the front tire 1st (X) as in 40/60. Weight balance can be affected by BP, acceleration and the engineering of the bike itself. I've read your entire post carefully and it did make me reconsider and organize my thoughts, and made me change my understanding of things. I agree with most of your corrections of my post: the inconsistencies you mentioned, the duration we stay at max lean angle (I agree it's not short at all), cause and effect of weight balance and acceleration/braking. I also Agree with your weight transfer comments, although for the sake of keeping this discussion and post focused (as much as it can be), I won't relate to them and will explain why. For the same reason I will also not relate here to the steering action itself. I do not agree with your claim that the turning radius keeps constant through the duration of max lean angle. This will be one of the conclusions towards the end of this post. I will 1st describe my understanding of straight line physics (acceleration/braking limits how they're effected from BP) to set basis for the cornering section of this post. My general understanding of things is that you cannot go much (if at all) beyond 100% weight on either wheel, either in braking or in acceleration. That's where BP can takes part. If your max theoretical acceleration is X(m/s^2) with a certain fixed BP (0/100 weight ratio), then its less than X if you sit more backwards, and more than X if you sit more forward (in each case, after we're at 0/100 weight balance). This is due to the angle formed at the rear contact patch between the combined CoG and earth (While braking: front contact patch). If you move your body forward while accelerating, you can accelerate at a larger rate than X before we reach this maximum 0/100 weight ratio. Same goes for braking. Moving backwards on the seat allows greater braking force to be applied before we reach the maximum 100/0 weight ratio, after which the rear comes off the ground and we cannot brake harder. It's obvious that the weight shifts backwards due to acceleration and forward due to braking. However, the amount of acceleration/brake-force that can be applied at any certain time is related to overall weight balance and maximum vertical force at each wheel. IMO, 3 factors can limit the rate of acceleration that we can apply: 1. Spinning of the rear wheel before we're at maximum possible weight on the rear (before 0/100 balance on a straight line) 2. Spinning of the rear wheel after we're at maximum possible weight on the rear 3. Front wheel coming up (In braking: locking the front before we're at max front weight, locking the front after we're at max front weight, and the rear coming up). - The 1st is related to the speed/balance/efficiency of the weight transfer process (combination of amount of acceleration and BP) - The 2nd is related to the maximum theoretical traction force from the rear (rubber/asphalt type, weight of the bike+rider) and rate of acceleration - The 3rd is related to BP and rate of acceleration. we need as much forward BP as we can to make that X as large as we can before the front comes off the ground. Although I think the 1st reason (weight transfer process) is both very important and frequent enough in practice, it can occupy an entire discussion by itself on one hand, and OTOH it can be discarded for the sake of this discussion of absolute limits by making all actions more progressively. It is greatly affected/improved by experience IMO. I'll disregard it for the rest of this post as it puts more variables into an already complex discussion, and it can be neutralized by changing the amount of acceleration/braking in a much slower rate. It will obviously harm lap times, but it's also unrelated to the maximum forces that can be applied at any given "fixed" state of the bike. So for the rest of this discussion I'll assume optimal weight transfers, and concentrate on the limits after we've reached "steady" states of weight balance. So that leaves us with the 2nd and 3rd points. I believe the 2nd and 3rd points are 2 implications of the same cause: we're at 0/100 balance (if on a straight line) and we try to accelerate more than the theoretical maximum. If we increase the rate of acceleration beyond the theoretical maximum too fast, the rear will spin. If we increase it slower beyond the maximum, the front will come up. The exact rate of speed of acceleration needed to differentiate between 2 and 3 is a direct function of the available traction (only forward on a straight line), and combined mass and CoG of the bike+rider: the smaller the mass or higher the "grip factor", the easier it will be to wheelie, the lower and forward (in braking: backwards) the CoG , the easier it will be to spin (in braking: lock) and vice versa. IMO BP can affect the 1st point and the 3rd point, but not so much the 2nd point. I think I didn't explicitly relate to "overloading" either tire although I probably related to this effect implicitly. Speaking of which, could you define "overloading" as you refer to it? I can interpret it as either closing the forks due to excessive braking force, not allowing enough weight transfer before we apply more braking/acceleration, apply more brake power than possible with current grip factor (regardless of forks state), excessive angular velocity which causes either wheel to run wide, etc. I think I'll be able to better relate to your post if we're clear on the terms we use. This was a straight line discussion (well.. at least my current understanding of things). I believe it is essential to try and understand straight line physics before we can discuss the extra complexity that cornering adds. At least for me, it makes it easier for me to "combine" and add the effects of cornering into this existing understanding. While leaning, on top of the vertical force (fixed overall but balanced differently on the front/rear depending on BP and acceleration/braking) and acceleration/braking forces, we also have a centrifugal force. The angular velocity of the bike and the bike's+rider weight define the amount of absolute force in that direction (perpendicular to the direction of the bike's progression). The angular velocity by itself is the only factor affecting the the amount of leaning needed to balance this force. Because this centrifugal force needs some traction resources to balance, that leaves less absolute traction resources to accelerate/brake. The larger the angular velocity (and directly related: lean angle) is, the larger the amount of traction needed to be devoted to keeping us on track and from sliding sideways, and the less freedom is available for acceleration/braking needs. In contrast to acceleration/braking on a straight line though, where we can shift 100% of the weight to one wheel for maximum effect, leaning requires a different "tactic". Now we're no longer interested in maximum acceleration/braking force, but we're interested in maximum centrifugal traction. If we want to achieve maximum cornering rate (= max angular velocity), we need maximum combined traction from BOTH wheels to achieve maximum absolute centrifugal traction. And this is where the 40/60 rule comes in handy. I agree that 40/60 (or a similar figure) is the balance that would give us most centrifugal traction (derived from the size of the contact patches). So how do we achieve this balance? Combination of BP and acceleration. To achieve maximum angular velocity/traction, we need the weight to be balanced 40/60. BP would affect it to some degree (I'm guessing not more than 5%), but acceleration is probably the most important "tool" in this regard. It has to be mild and steady such that the weight moves backwards from the natural 50/50 of a still bike+rider, to 40/60 of an accelerating bike (let's call it "40/60 acceleration"). As long as we're at our max lean angle, the same acceleration should be kept, to keep us at 40/60 balance. The closer we are to the maximum possible absolute angular velocity (and lean angle), the less reserves of "forward traction" we have, and therefore the less freedom we have to change that balance and our 40-60 acceleration, or else, one of the wheels will break loose. To cause one of the wheels to break loose, it's again one of the 3 reasons I've stated earlier in this post, with two differences: 1. There's much less traction that can be devoted to acceleration/braking, due to the resources devoted to centrifugal traction, and we're therefore mostly limited to spinning the rear (/"locking" the front) and we don't have to worry about the front coming up because there isn't enough driving traction left to make it happen (It may happen later though, when we're more straight on the last phase of corner exit, again, depending on grip factor of the tires/asphalt). 2. There's now a new 4th possible reason: We can also lose traction sideways (due to centrifugal force) on either wheel. Since the 3rd reason is irrelevant here, and we're neutralizing the 1st one, we're left with the 2nd and 4th reasons. To get to the 2nd reason (spinning the rear due to more than max possible forward traction or locking the front for the same reason): accelerating at a too fast rate will spin the rear, braking with the front at a too fast rate will make the front lock. "Too fast" is very small here since we're at very little "forward traction" reserves now. That's why we need the throttle control: to keep the acceleration as fixed as possible. To 4th reason (sliding sideways) comes into play when we have more angular velocity than either tire can hold. This can happen if we're at 40-60 acceleration but we lean (make the angular velocity higher) more than the maximum possible: both tires slide (I guess this one is quite rare?) or if we get closer to maximum lean angle but we're accelerating at less than 40-60 or closing the throttle to get the same result (more weight on the front, it will break lose sideways 1st) or if we're getting close to max lean angle at a higher acceleration than 40-60 (more weight on the rear, it will break loose sideways 1st). So to maximize angular velocity, we need that 40/60 fixed acceleration as long as we want to keep max lean angle. This brings an interesting issue of what "cornering speed" is. Derived from this analysis, we can see that this is a problematic term, since the cornering speed is not constant through the entire "max-lean" duration. To have a constant lean angle and angular velocity, we need constant acceleration. But cornering speed is not constant, and neither is the turning radius. Corner speed gets progressively faster and the turning radius gets progressively bigger WHILE we're at max lean angle. This brings me to your claim about widening the arc/radius. As it turns out both from my analysis and from TOTW books (acceleration is required throughout the entire "max lean" duration), this 40/60 forward acceleration is required for max lean angle. If lean angle (and angular velocity) is kept at max constant for this entire phase, but the bike is going faster and faster (40/60 acceleration), the arc MUST widen since the bike cannot keep the same radius and lean angle while going faster and faster. As we exit the corner towards the straight and straighten the bike up, the angular velocity decreases, more traction is available for acceleration, the arc widens at an even faster rate (infinite arc on the straight) and reason 3 comes back into consideration. Phew.. this was probably my longest post ever on any forum. Please excuse me that I haven't directly related to all of your points (at least I agree with most). As it turned out, I was sorting my thoughts and understandings of cornering while writing, relating directly to your points less that I've intended. However, I did enjoy writing this post very much, and I think it presents the issues of cornering limits (excluding issues of the process of weight transfer itself and steering action) both in a manner that complies with the facts/tips/instructions of Keith's books, and in a manner I can relate to with reasoning. Again, my theory and understanding are open for discussion by anyone. cheers.

I tried to compare Ben Spies' pic (good one sleeper ) with a pic of mine from a similar perspective. Had to flip my pic horizontally to make it easier to compare (mine is originally a right turn) and I can see few noticeable differences: - Obviously, he has a much steeper lean angle than me - He hangs off way more than me - His butt is completely out of the seat - His upper body "plane" is diagonal to the bike (vertical to earth), while mine's parallel. Probably an outcome of hanging off more? - Similar outer foot position on the outer peg - I think his outer knee doesn't touch the tank, mine does. I don't want to change that for now as it feels comfortable to me to be locked to the tank. - His inner ankle position is very different than mine. His is almost vertical, mine is almost horizontal with the ankle bent a lot. I think the last point is what I was looking for. The other points are clear and I'm mostly aware of them (whether they're OK or need improving). The last point about inner ankle position is something that I wasn't aware of. It always felt a bit strange to me that I have to bend the ankle so much to be able to keep my toes (and not the middle of the foot) on the peg, but I thought it's due to my height. Maybe it is and maybe it isn't, but it's definitely something I should spend some attention at. I know that it feels to me that I have much weight in the inner peg, and now that I think of it, maybe it's due to the stress on the bent ankle. But if the ankle is more "open" and the foot more vertical, how does that supports my weight? bahh.. gonna have to experiment with that. Good me for noticing something new and thanks again for the pic sleeper!

Apology accepted. IMHO, that post does include some interesting issues for discussion, on topic.

Racer, as you've managed to forget by now, I have read those books and I do have them. In case you haven't noticed, I added "IMO" to many of my points, which clearly states that this is my personal opinion and not some facts from heaven (the same applies to Keith's books and teaching BTW, with the advantage of his great experience). You asked twice for my opinion about your thoughts and I gave it, with much details. I had the feeling we're having a discussion about body position and weight transfer before turning, during and on turn exit. I've posted my thoughts on the subject and my interpretations. If you think it's worth commenting, pls do so. If you don't find it interesting, or you think it's not worth reading because you interpret it as contradicting to CSS methods, just skip it. 'nuff said.

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

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.

This can be endless. I'm out, and back on topic, if it ever surfaces again. peace.

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

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