racer
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Cobie,
Participating here on this forum has benefited me in many ways. I have attended a half-dozen schools at several different tracks over the years and have been studying my Twist bibles for over two decades. However, being able to discuss specific aspects of the material and curriculum with other members, "hearing" their unique perspectives, interpretations and personal experiences has been an invaluable resource for me. Whether firming up or fleshing out incomplete or merely intuitive understanding of some aspects, or introducing me to other aspects I've never considered, my time here consistently leads to a fuller, more complete understanding of all aspects of my riding.
In addition to helping me gain a better understanding of motorcycle theory and riding techniques, this forum has helped me to realize that, although much has changed since I retired from the field of battle, much has remained the same and I still have something to offer, something of value to give back to the sport that has given me so much.
And, through forcing myself to mentally organize my thoughts, memories and experiences and attempting to verbalize that, this forum provides a unique opportunity to develop and practice my communication skills through a subject I am passionate about with a broad audience who shares my passion in a genuine, open and egalitarian atmosphere. What writer could ever dream of or ask for more?
As for specfic threads or topics, I find them all valuable. Whether it is physics theory, machine set-up, some specific riding technique or simply the finer points of riding the Nurburgring, being here has reminded me that the game never ends and there is always more to do and to learn. (Not only about what is already known, but, maybe even about what isn't known... yet.) And how much there still is to do. How many new roads to ride. New technology to master. New riders to help or inspire. And perhaps, if I'm very lucky, to humbly contribute something to the bleeding ragged edge of the science and knowledge base of our ever evolving sport. Not merely for our benefit or to honor the work of those who laid the foundation, but, mostly for those yet to "discover the art". The future is so wide open. What a wonderful feeling.
My sincere and genuine thanks to CSS for hosting this forum and to all our members for your ongoing efforts, sharing your views, perspectives and, most importantly, your questions. That is where it all begins.
racer
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I recently posted a warning and then reported a spam post in this thread that contained a link with embedded spyware. In the process of cleaning up the spam, admin apparently deleted not only my heads up to other members to not click on the spam link but also my (admittedly long-winded) on topic reply to Cobie's survey question.
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One sensation that I have in slow corners is that I feel like I can not lean the bike as far as in a fast corner. For some reason the slower speed gives me the feeling that I don't have enough momentum to actually keep the bike up. This is just a sensation that I get when trying to turn in to slow corners, almost like a sensation that the bike will just fall over.
I had the same experience, and at CSS when I mentioned this difficulty, the reponse was something like "Do you know what lean angle you are trying to achieve?" and "When you get there, how do you stop the bike from leaning over more?".
... I was not being precise about when to stop pushing on the bar- I was just trying to quick turn it over then hope for the best.
... I was just not thinking about the fact that when you lean the bike, you can stop the lean or even stand it back up. Once I got more in control of this, I picked up my pace and that made it much easier, too, because the bike was harder to turn and felt more stable.
*slaps forehead*
That is an awesome answer, Hotfoot.
Another, more minor point is to check out the profile of your tires - some tires seem to want to jump to a certain lean angle, which may feel too abrupt in a slower corner, and you may want to look at your suspension setup, if you have the front end a bit low or soft you may find that the bike steers very quickly, and if it's too touchy it can make you feel like a quick turn would dump you right over.Excellent post.
(ETA: Not that you need my imprimatur. I just wish I had thought of it.
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I've just been looking at RA T7 on Google Earth and I'd have to say that the proper turn point is beyond the end of the left side curbing as you approach the corner. I don't know how old the sat-photo is, but, there appears to be a patch right there on the left side and, without being there, I'd go to the end of that patch and a bit further before flicking it in on my 125. A bigger bike with more motor to use, maybe even a tad deeper to square it off for a good drive onto the back straight.
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I have no idea what you mean...
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For what' it's worth:
I rode four track days, and cornerworked a bunch. Then I took second place in my first race, and won my second race.
If all you want is to have a picnic at the track, sure, keep up the good work. Bring the wife and kids and grandma too.
You obviously have what it takes.
What are you waiting for?
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Well, you obviously have no problem with lean angle.
If you aren't running front of the pack lap times for the local race club and top 10-15 AMA pro times... something is missing.
Aside from some top notch coaching, my guess is that it might be a little competition. Perhaps it's time to skip the track day and go race.
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Here are a few. I'll post more later when I have more time. You just need to remove the extra space before the last character to activate.
:lol : =
: ) =
; ) =
: P =
I can't make the smiley board here work so I use the ones I've collected over the years. Some work here, a few of my favorites don't.
later
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All the racers I know (and I imagine track riders, too) do remove those "feelers".
Are you using all of your tire out to the edge with those feelers in place?
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Let's stop thinking about the bike decelerating and think about constant drive or acceleration while applying the rear brake.
Why? Acceleration (or lack of it) is the single defining parameter for weight bias (and the most common condition that any motorcyclist might find oneself in when seeking more traction from the rear wheel).
It stands to reason that as the back of the bike comes down (due to chain pull, as I have proved to myself on my own bike), the front must become lighter as the motor is effectively now trying to revolve the rest of the bike around the back wheel. More weight = more traction.More acceleration equals more weight on the rear wheel. Any brake equals less acceleration.
Less acceleration equals less weight on the rear wheel. Period. (Have you read A Twist of the Wrist?)
Or do you think you can pop a wheelie by applying the rear brake? (I think a world full of stunt riders would disagree.)
Here's my rear brake test:
Go pop a wheelie and apply the rear brake. What happens?
I see your point.
But acceleration is only possible should the rear wheel have traction. A rear wheel spinning faster but not gripping does not equal acceleration and no further weight transfer is happening.
Let's try to apply your "theory" to a real world situation then.
If I was stationary stuck in the mud or snow, applying the rear brake would do nothing as I am not moving. However, I could slide my fat butt back and (compressing the rear suspension in the process) transfer a bit of weight to gain some traction. But that is due to my butt moving, not the suspension compressing. And, in that scenario, dragging the rear brake if the rear wheel was spinning, might compress the rear and cause the bike to slope rearward which might alter the static weight balance toward the rear to help the spinning wheel bite (but not very much).
Once I start moving out of the mudhole, continuing to drag the rear brake might help to the degree that the rear wheel continues to spin, but, the more traction I get, the more it will transfer potential weight forward, ie. without the brake, I could accelerate harder and transfer more weight rearward than applying the rear brake might, if it could. Remember the wheelie example. It's primary effect would be to slow me down now that I am making progress out of the mudhole. Once in motion (accelerating), the only practical use I can think of would be to slow or stop the spinning wheel (to help gain traction)... like it was designed to do. But, that is about slowing the spinning wheel more than weight transfer. Which is why advanced roadracers (and I imagine dirtbikers) on especially powerful machinery use it when exiting corners to control rear wheelspin under acceleration, not to transfer weight to the rear for more traction. They are already transfering exponentially more weight under acceleration than dragging the rear brake ever would if it could.
My point once again is that you can accelerate while applying rear brake creating drag which causes the rear spring to load, transferring weight to the rear wheel creating more traction.No. Loading of the rear spring in that scenario is not due to weight transfer, it is due to force from the motor being transmitted to the spring via the rear suspension geometry.
I don't know if I can put it any clearer than that. It's probably more an issue with dirt bikes so let's forget it.Wheelies have never been my forte unfortunately.
Blah blah blah. PUSSY. You're really quite a whiney little sod aren't you? Typical bully that runs away when he can't win or gets his nose bloodied a bit.
(ETA: This last was meant as an in kind jestful poke for continued and unneccesary name calling by you here in this thread, Willy. We've been able to avoid the flaming and other sorts of personal attacks found on other forums here and I think it would be nice if we could continue to do so. Thanks.)
That said... dirtbikes have never been my forte. In any case, any acceleration will do more to transfer weight to the rear than the rear brake ever could... if it could at all once you begin to accelerate. Once you are moving, the "weight transfer" created by the brake goes forward no matter the slope of the bike rearward.
Look, I see the picture of mechanical forces you are trying to paint. But, just like the effect of chain pull compressing the rear suspension is far outweighed by the effect of the accelerating rear wheel which overhwelms it, the potential for weight transfer you imagine is far outweighed by the weight transfer of acceleration. I fail to see any practical value beyond controlling wheelspin... like it was designed to do. Which is more about the wheel than the weight.
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Or you could just remove the feeler tips from your footpegs...
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I had my 2nd track day since Level I school a year ago; I'm gradually improving and getting faster and generally feeling better about my riding. And having a LOT of fun!
One thing that happened this time was I scraped the feeler peg on my foot rest. At first I thought it was my boot but after I got back to the paddock I realized it was the peg. On two different sessions I did the left side and the right side.
If I've done this but I'm not dragging my knee puck, is that a good thing or a bad thing? I'm not trying to drag anything as a goal in itself.
Depending on details we don't have, I can think of three possible helpful alternatives:
1. A deeper turn point combined with 2. A faster flick can decrease the amount of lean angle needed to complete the turn. 3. Hanging off more, or a more properly positioned body, can decrease the overall amount of lean angle necessary.
But, like Kevin said, this depends on details we don't have. Perhaps if you post a photo/video we could offer more accurate information for your situation. However, ultimately, reading the Twist of the Wrist books and attending a school is the final answer.
r
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Let's stop thinking about the bike decelerating and think about constant drive or acceleration while applying the rear brake.
Why? Acceleration (or lack of it) is the single defining parameter for weight bias (and the most common condition that any motorcyclist might find oneself in when seeking more traction from the rear wheel).
It stands to reason that as the back of the bike comes down (due to chain pull, as I have proved to myself on my own bike), the front must become lighter as the motor is effectively now trying to revolve the rest of the bike around the back wheel. More weight = more traction.More acceleration equals more weight on the rear wheel. Any brake equals less acceleration.
Less acceleration equals less weight on the rear wheel. Period. (Have you read A Twist of the Wrist?)
Or do you think you can pop a wheelie by applying the rear brake? (I think a world full of stunt riders would disagree.)
Here's my rear brake test:
Go pop a wheelie and apply the rear brake. What happens?
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Ok, now we're getting somewhere.
TWIMC:
I grabbed my favorite technician at lunch today and we performed the rear brake test on several different motorcycles including a shaft drive cruiser, an old cage frame swingarm standard and a 2003 CBR600RR. (A big thank you to the anonymous service customers who unknowingly donated their bikes to unwittingly participate in this international forum test program
).The results on the cruiser bike and near vintage standard were indeterminant at best. The shaft drive and cage frame swingarm had no perceptible motion.
The CBR600RR squatted like a b!t@h in heat.
That said... I need to eat before I throw a wobbly.
BRB
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Wheelbase lengthening really doesn't come into it but yes, wheelbase will lengthen. So what? It's not as though there is any resistance to lengthening the wheelbase after all there is no wall in front of you same as there isn't when you are racing/riding.
Right. Only the mass of the machine and rolling friction to resist forward acceleration...which you don't have with the rear brake on. Not sure how good of a test this is either. Only one cuppa so far and I gotta leave for work. I'll think more about it.
As for video, I don't think so. How 'bout you sit on your bike in your garage, start it up, put it in first, apply the back brake, let out the clutch and you tell me what happens. It'll take about a minute. I've just done it.What kind of bike do you have?
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Applying the rear brake decreases acceleration, on or off the gas, and adds more weight to the front. Period.
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The rear brake is used as an advanced skill in several types of situations in road racing. Can you be more specific about how using the rear brake will redistribute weight "for beter traction/drive"?
Thanks,
racer
G'day Racer
I've given this some thought and decided that this is what happens...
By applying the rear brake with the throttle on means something has to give. If the motor is unable to turn the rear wheel or has resistance, then it would want to spin itself around the rear wheel thus biasing weight towards the rear which in turn creates more friction between the the tyre and surface which enables more traction.
Does this sound plausible?
Willy
Applying the rear brake adds more weight to the front, not the rear. And, in any case, adding more weight and braking force together to the same wheel, front or rear, increases the load and stress on the contact patch which typically reduces the amount of available traction. If the front wheel is light to begin with, for instance when you are cresting a hill, dragging the rear brake can add weight to the front and help create more traction at the front. But, even if you are accelerating, dragging the rear brake counter-acts the acceleration and weight transfer to the rear, hence, why you can control a wheelie with the rear brake or bring the front down with it.
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G'day Racer,
Put the bike in first and apply the rear brake. Let out the clutch. What does the back end want to do? It wants to go down. It does NOT want to pull the swingarm underneath the bike.
So, contracting chain pull under acceleration tries to lengthen the wheelbase?
Can you post a video of you conducting your experiment that demonstrates the rear compressing?
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Big Willy,
I am well aware that a motorcycle drive chain gets tighter as the swingarm compresses and the rear axle travel describes an arc. With respect, that fact has nothing to do with the subject at hand unless the chain is improperly adjusted and binding under compression.
Aside from the bike that you said "BMW has out" and some experimental racing machines with adjustable swingarm pivots, the chain and swingarm of the majority of motorcycles are not parallel. Hence, being that the swingarm is typically oriented downward, chain pull applies downward force to the swingarm. One need only look at a motorcycle up close to see this. As for Rossi's bike, I don't know how its swingarm pivot is oriented, however, while chain force applied to a typical swingarm may resist compression, it is not necessarily enough to prevent all compression. And, at the end of the day, that resistance to compression turns out to be a good thing for getting a good drive out of a corner. I already covered this in my second reply to Leftlaner near the top of this thread.
For the record, I never claimed that chain pull was the dominant force responsible for motorcyle suspension extension under acceleration. I said that, as the only link to the primary driving force of the machine, it was ultimately responsible; but, that it was only one of the component forces directly involved. I thought it might be interesting to discuss which component of force might be dominant in that process. Unfortunately, you seem to be of the opinion that chain pull isn't involved. So, perhaps somebody else will pick up that stick.
Good luck,
racer
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Hi Shane,
Don't forget about your RP's. A lack of RP's will also bring on that feeling.
r
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BMW have a bike out at the moment that has the gearbox sprocket shaft in line with the swingarm pivot , effectively maintaining constant and consistent chain tension.
Several manufacturers jumped on the band wagon of the work being done by folks like Scott Russel/Muzzy? Kawasaki/GMD fifteen years ago.
It isn't really about chain tension, it is about the angle at which the force is applied between the chain and swingarm. The greater the angle, the more effect the chain pull/acceleration has on the rear suspension.
It seems that some think because of the triangulation things at play (i.e. the chain is at it's tightest when the swingarm pivot, the gearbox shaft and the rear axle are in line) that the chain is happiest trying to pull the swingarm underneath the bike.I'm not really clear what you mean here. It isn't about the chain "being happy" it is about the angle between the chain and the swingarm.
Really putting the front wheel against a wall is more about the drive wheel wanting to shorten the wheelbase which ever way it can, be it compressing the forks or drawing the swingarm underneath the bike.Well, in reality, it won't compress the forks because the bike is trying to wheelie. But, my question is whether chain pull has more effect than the rear wheel trying to claw its way under the bike on lifting the rear suspension, ie. which is the dominant component vector responsible for raising the rear.
I guarantee that if the same experiment is commenced with the swingarm facing down toward the swingarm pivot point, then the chain would pull the swingarm up lowering the bike.In other words, the chain isn't that fussy, it's more about the angle of the swingarm and the spring's ability to maintain that angle.
By jove, I think he's got it!
To look at it from another way is to say that if the force to overcome the triangulation (whatever it's called) is so great, then suspension wouldn't be necessary as we'd effectively be riding rigid rearends (aka WLA's revisited).Precisely! That is exactly what happens under acceleration. We are effectively riding rigid (or more rigid) rearends.
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For the record, several motorcycle manufaturer/racing teams along with GMD Computrak experimented with altering the position of the swingarm pivot on superbikes and GP 500's about ten years ago culminating in race bike frames with adjustable eccentric swingarm pivots an an attempt to eliminate chain pull from the equation. In fact, I believe Eddie Lawson and some other guru around here experimented with MX style chain roller/guides to limit chain pull back in the 1980's. At the end of the day, I believe the common consensus was that a little pull on your chain was a good thing.
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To whom it may concern:
Once you accept or grok that chain pull is always working to extend the suspension, raise the rear of the bike and/or pull the swingarm down, the next realization is that the forward motion of the rear wheel is also trying to push itself under the bike (ultimately lifting the front wheel) which also works to extend the suspension, raise the rear and/or pull the swingarm down.
So, there are actually two "component force vectors" being applied to the swingarm to create one "composite" force vector. At that point, the question becomes, which component is dominant or stronger, ie. which is more responsible for the fact that the rear of the bike raises up under acceleration? Chain pull acting to pull the swingarm down? Or the forward force of the rear wheel trying to push itself under the bike?
And then, just how dominant is that component? Are they relatively close or is one WAY stronger than the other? And does that relationship remain consistent across the acceleration curve?
racer
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Thank you to the anonymous guest I found reading this thread on the last click list. TheJonesBoy's primer is awesome and touches on several recent discussions we've had here about the physics of contact patches and gyroscopic precession. Balistic's posts are relevant, too. Great stuff!
Although none of the current threads are discussing this specific subject(s), there is at least one "physics" thread at the moment, and, I felt some of us might appreciate and benefit from it.
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Zx6r Question
in School Questions/General Discussion
Posted
Are you referring to the school bikes?
I have no idea if they are running the stock gearing. I'm sure Willy (Balistic) could tell you if you shoot him a PM or an email.