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40 Foot Circle


Jaybird180

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Poor technique has nothing to do with it, the 50 degrees is an example of a lean angle at 2 different speeds! no matter what your lean angle is a 100 mph turn will always be a bigger radius than a 40 mph turn!

 

 

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of course, but as I say the 50 degrees is just a figure for example it could be 20 degrees if thats easier for you and at that lean angle or any lean angle for that matter the faster the speed the bigger the radius!

I'm saying that is is NOT correct that for a fixed lean angle turn radius is ALWAYS directly proportional to speed. I'm saying that there are other factors can vary this, poor technique being just one.

 

How about another?

Dani Pedrosa and Nicky Hayden: same bike, same lean angle, same corner speed...Dani can turn tigher than Nicky.

 

Riders like Capirossi are perfect for this discussion. I've heard that his cornerspeed is usually within 1/10th of a kilometer on successive laps, and that he can hit nickels lap after lap with his RPs. I wonder what he'd say?

 

 

Dani and Nicky both have very different riding styles, Dani breaks the rear loose at the apex and picks the bike up at the same time as he rolls on the throttle squaring the last part of the turn and giving him maximum drive at the corner exit, (as per the pickup drill)! If Dani and Nicky were to take a corner at the same lean angle they would not be at the same corner speed, Dani's lighter weight would mean he would have to lean further to match Nicky's speed!

 

I dont know what Capirossi would say but I think you will find that all of the top level racers in the world are able to hit the same part of the track lap after lap using good RPs though I cant see where that is relevant to the topic we are discussing!

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Good technique or bad technique, does it really matter? No, it doesn't. No matter if you have bad tech or good tech, there is a max for what you can do. Good technique obviously would help in being faster and turning a tigher line, but thats isn't what you are changing in this "40 Foot Circle" question. You are adding trottle, and body technique doesn't change the rate of throttle. It only puts a different maximum on the speed, lean angle, or how tight you could carve a turn. It doesn't change the simple fact that the faster you go through a turn at a given lean angle will increase the radius that you can carve.

 

W/ Pedrosa and Hayden, you are comparing apples to oranges. The question that started this topic wasn't wether rider A could turn a tighter lap at a given speed, lean angle, than rider B.

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Good technique or bad technique, does it really matter? No, it doesn't. No matter if you have bad tech or good tech, there is a max for what you can do. Good technique obviously would help in being faster and turning a tigher line, but thats isn't what you are changing in this "40 Foot Circle" question. You are adding trottle, and body technique doesn't change the rate of throttle. It only puts a different maximum on the speed, lean angle, or how tight you could carve a turn. It doesn't change the simple fact that the faster you go through a turn at a given lean angle will increase the radius that you can carve.

 

W/ Pedrosa and Hayden, you are comparing apples to oranges. The question that started this topic wasn't wether rider A could turn a tighter lap at a given speed, lean angle, than rider B.

 

exactly right, technique is not an issue here, if a rider has bad technique through a 40 mph turn dictated by his own riding style then he's bound to be using that same technique in the faster turns. Anyway getting back on topic with the 40 foot circle, here in the UK alot of guys use roundabouts to get their knee down, the bike press even have vids of this on you tube, what they show you is a guy going round the roundabout hanging of the bike until his knee touches down! that shows me that they must be adding lean and throttle at the same time, dangerous! So I thought of what would happen if you went to a roundabout and did what jaybird asked in his original question and really 1 bike increase this 40 foot diameter circle. is all that would happen!

 

not what I would practice

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Dani and Nicky both have very different riding styles, Dani breaks the rear loose at the apex and picks the bike up at the same time as he rolls on the throttle squaring the last part of the turn and giving him maximum drive at the corner exit, (as per the pickup drill)! If Dani and Nicky were to take a corner at the same lean angle they would not be at the same corner speed, Dani's lighter weight would mean he would have to lean further to match Nicky's speed!

 

I dont know what Capirossi would say but I think you will find that all of the top level racers in the world are able to hit the same part of the track lap after lap using good RPs though I cant see where that is relevant to the topic we are discussing!

 

I can see your point, as my bringing up Capirossi does seem off topic. Perhaps I could have said it this way:

 

1- Observation <> (does not equal) conclusive

2- There's a problem with the logic stated above and that problem comes in when we use words that hint at "always".

 

Mathematically speaking, it's been stated that:

Rider at x lean angle, y speed = z turn radius

Rider at x lean angle, y+q speed = z+ [q (factor)] turn radius

Although this may be correct in some circumstances, it is not consistent across the board.

In other words, there are times:

Rider at x lean angle at y+q speed <> z+ [q (factor)] turn radius

And poor technique is not the ONLY reason to account for this.

Here's a personal experience example (we're waaaaaay off topic here, but whattheheck, right?)

 

A couple of years ago at ViR Patriot during my 5th session of the day, I'd gotten happy with my consistency. I could hit the TP, apex, exit nearly blind in a particular section; I was on it! (or so I thought) I was already at max lean for my given BP as I had consistent knee pressure on the tarmac. I changed NOTHING else during that session, except going in faster and faster and getting on the gas harder and harder, yet my turn radius didn't yet change until I was ready for it to. Why not? I was too slow and nowhere near the edge of performance. I was in the top of my riding group, but there were groups that were much faster. Once I loosened up with the new speed and allowed the bike to get closer to the rumble strip on exit did my turn radius change. Then, I could go even faster.

 

 

Nevertheless, I had accepted the answer as posted by HOTFOOT from Will (which coincidentally was hinted at earlier:

Simple question, but with some not-so-simple considerations. …

 

However, there is another input to the steering than rider input and tire input, and it caused by steering trail. Suppose you had a bike on its centerstand (racers can ask tourers what that is), resting lightly on its front wheel. With its steering centered, push on the left side of the bike tank. You'll see the steering shift right, because the front tire contact patch is behind the point where the steering axis meets the pavement. I think that, as speed increases in a turn, the trail-induced forces tend to steer away from the direction of turn, which would act to increase the lean angle. Therefore, I suspect that a bike with enough trail might actually lean more into a turn, and actually decrease the turn radius, as speed increases. On the other hand, a bike with an intermediate amount of trail might actually tend to increase lean angle exactly enough to maintain a constant radius turn as speed increased-- with zero rider input to steering!

 

The latter condition sounds like nirvana-- you could fool around all you want with the throttle (within the traction limit), and not affect your line through a turn at all! (But, being a ######, Nature probably exacts some nasty other form of penalty for such a virtue.)…...

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Dani and Nicky both have very different riding styles, Dani breaks the rear loose at the apex and picks the bike up at the same time as he rolls on the throttle squaring the last part of the turn and giving him maximum drive at the corner exit, (as per the pickup drill)! If Dani and Nicky were to take a corner at the same lean angle they would not be at the same corner speed, Dani's lighter weight would mean he would have to lean further to match Nicky's speed!

 

I dont know what Capirossi would say but I think you will find that all of the top level racers in the world are able to hit the same part of the track lap after lap using good RPs though I cant see where that is relevant to the topic we are discussing!

 

I can see your point, as my bringing up Capirossi does seem off topic. Perhaps I could have said it this way:

 

1- Observation <> (does not equal) conclusive

2- There's a problem with the logic stated above and that problem comes in when we use words that hint at "always".

 

Mathematically speaking, it's been stated that:

Rider at x lean angle, y speed = z turn radius

Rider at x lean angle, y+q speed = z+ [q (factor)] turn radius

Although this may be correct in some circumstances, it is not consistent across the board.

In other words, there are times:

Rider at x lean angle at y+q speed <> z+ [q (factor)] turn radius

And poor technique is not the ONLY reason to account for this.

Here's a personal experience example (we're waaaaaay off topic here, but whattheheck, right?)

 

A couple of years ago at ViR Patriot during my 5th session of the day, I'd gotten happy with my consistency. I could hit the TP, apex, exit nearly blind in a particular section; I was on it! (or so I thought) I was already at max lean for my given BP as I had consistent knee pressure on the tarmac. I changed NOTHING else during that session, except going in faster and faster and getting on the gas harder and harder, yet my turn radius didn't yet change until I was ready for it to. Why not? I was too slow and nowhere near the edge of performance. I was in the top of my riding group, but there were groups that were much faster. Once I loosened up with the new speed and allowed the bike to get closer to the rumble strip on exit did my turn radius change. Then, I could go even faster.

 

 

Nevertheless, I had accepted the answer as posted by HOTFOOT from Will (which coincidentally was hinted at earlier:

Simple question, but with some not-so-simple considerations. …

 

However, there is another input to the steering than rider input and tire input, and it caused by steering trail. Suppose you had a bike on its centerstand (racers can ask tourers what that is), resting lightly on its front wheel. With its steering centered, push on the left side of the bike tank. You'll see the steering shift right, because the front tire contact patch is behind the point where the steering axis meets the pavement. I think that, as speed increases in a turn, the trail-induced forces tend to steer away from the direction of turn, which would act to increase the lean angle. Therefore, I suspect that a bike with enough trail might actually lean more into a turn, and actually decrease the turn radius, as speed increases. On the other hand, a bike with an intermediate amount of trail might actually tend to increase lean angle exactly enough to maintain a constant radius turn as speed increased-- with zero rider input to steering!

 

The latter condition sounds like nirvana-- you could fool around all you want with the throttle (within the traction limit), and not affect your line through a turn at all! (But, being a ######, Nature probably exacts some nasty other form of penalty for such a virtue.)…...

 

Couple of points here. First of all, the quote above is not the one I posted from Will. It is a bit similar, but it ain't de same, it was posted by, and written by, someone else. I thought Will's answer was easier to understand.

 

Second - what Will DID say was that trail will cause the front wheel to turn to a stabilizing point. That was making the LARGE assumption that the rider allows it to do so. I couldn't quite tell from your post if you were loose enough on the bars to allow that to happen. Also at risk of complicating the discussion, I think the fact that you were dragging a knee changes things like the effective lean angle (if you taking a little downforce on your knee) and creates a little drag on that side. Once you introduce the concept of a highly mobile rider the math gets so much more complicated that my brain freezes. :blink:

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Hi, first time on this forum. Thought the question and answers were interesting and felt like posting a reply. Basically, if all forces acting on the bike are kept constant, the bike's direction and speed and radius will not change (Newton's First law). If you change one of the forces acting on the bike - in this case applying throttle - the behaviour of the bike will be changed until it reaches a new equilibrium state - in this case in the form of a wider radius (Newton's Third Law). The reason is this:

 

Applying throttle increases the force exerted by the tyre on the road beneath it. This force is at a lean angle, but can be described as a function of a straight downward vertical force and a straight horizontal outward force. Accordng to Newton's Third Law, the road (Earth) exerts an opposite and equal force on the tyre, ie upward and inwards, effectively causing the tyre to be pushed in and under the bike, raising the bike and increasing the angle.

 

Applying throttle raises the bike, it's that simple. If you increase the speed of your bike in a corner and you don't widen your radius, it's because you lean in more or apply bar pressure, even if it's only slightly.

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Wonderful, complex and exciting conversation. Thanks to all this input, I'm happy to believe that miles per hour = radius. Of course we all try this experiment every time we apply Throttle Control Rule #1.

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Wonderful, complex and exciting conversation. Thanks to all this input, I'm happy to believe that miles per hour = radius. Of course we all try this experiment every time we apply Throttle Control Rule #1.

 

The circle will widen with added throttle eventually, if that wasn't obvious in all the back and forth.

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I skimmed through a lot of this discussion and didnt notice anybody mention the suspension's affect on the radius of your turn. If you roll on the throttle the forks changes the bikes geometry. Longer forks tubes mean slower turning for a given lean angle. Conversly the brakes compress the front increasing the rate at which the bike turns for a given lean angle. All of which comes together somehow to explain what Keith is trying to teach us.

 

For instance, on the way in to a turn you are deaccelerating so the forks are compressed helping you tighten the line without adding lean angle. On the way out you are hard on the throttle causing the tubes to extend and widen the line. If the line is too wide you can slide yourself up on the seat and lean your chest a bit lower to put more weight up on the front to tighten the line back up without adding lean angle.

 

But I'm pretty confident the CSS guys can explain it better than I have.

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I have always had the same idea, that braking cause the front to drop and the steering angle to sharpen, easing the change of direction. However, after being challenged by the instructors here, I have made an effort to actually pay attention to what is happening instead of simply relying upon what I have read. And I can assure you that my Triumph, at least, requires significantly more effort to turn when hard on the brakes than with little or no slowing down. It is also very apparent that it wants to run wide under acceleration.

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I have always had the same idea, that braking cause the front to drop and the steering angle to sharpen, easing the change of direction. However, after being challenged by the instructors here, I have made an effort to actually pay attention to what is happening instead of simply relying upon what I have read. And I can assure you that my Triumph, at least, requires significantly more effort to turn when hard on the brakes than with little or no slowing down. It is also very apparent that it wants to run wide under acceleration.

 

I'm not really too concerned with how much effort I have to put in to turning the bike. Good body position puts you in position so that you are pushing perpendicular to the bars so all the effort acts to turn the wheel. If you are still on the brakes when you start your turn then absolutely it will require a little more strength which makes perfect sense: At that point in time there is more weight on the front tire than the back. You'll also perceive more weight because you are having to hold yourself up against the forces trying to send you over the handle bars. Good fun.

 

To address the effort required: I do 100 push ups every morning. :)

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I have always had the same idea, that braking cause the front to drop and the steering angle to sharpen, easing the change of direction. However, after being challenged by the instructors here, I have made an effort to actually pay attention to what is happening instead of simply relying upon what I have read. And I can assure you that my Triumph, at least, requires significantly more effort to turn when hard on the brakes than with little or no slowing down. It is also very apparent that it wants to run wide under acceleration.

 

I'm not really too concerned with how much effort I have to put in to turning the bike. Good body position puts you in position so that you are pushing perpendicular to the bars so all the effort acts to turn the wheel. If you are still on the brakes when you start your turn then absolutely it will require a little more strength which makes perfect sense: At that point in time there is more weight on the front tire than the back. You'll also perceive more weight because you are having to hold yourself up against the forces trying to send you over the handle bars. Good fun.

 

To address the effort required: I do 100 push ups every morning. :)

 

 

Ha! When I watched Twist of the Wrist II on DVD I laughed out loud at the part where the to new riders were talking about getting to the gym because their arms were all pumped from (incorrectly) riding. I had the same thought after my first track day. This was before I did CSS levels 1-2. I would have to pit early or skip sessions because I was so worn out.

 

I just did two track days in a row at Talladega GP and didn't have any of these issues. I was fresh and ready to go the second day. ;)

 

Kelly

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Ha! When I watched Twist of the Wrist II on DVD I laughed out loud at the part where the to new riders were talking about getting to the gym because their arms were all pumped from (incorrectly) riding. I had the same thought after my first track day. This was before I did CSS levels 1-2. I would have to pit early or skip sessions because I was so worn out.

 

I just did two track days in a row at Talladega GP and didn't have any of these issues. I was fresh and ready to go the second day. ;)

 

Kelly

 

I've never noticed that it takes that much effort to turn the bike. It isnt a brute force afair. In fact I'd say that if you try to brute force the bike it will toss you on your butt for the trouble. After a really good track day its my brain and thighs that are tired. My wrists are usually sore too because I use them too much to hold myself up under braking (having one pinned and glued together doesnt help). But the big deal is the brain, after a full day of riding (usually get 6 30 minutes sessions) in 90+ heat, I'm more zombie than human. Luckily the trailer is easy to load, the drive home is short (I live about 35 minutes from the track) and then I can put on a swim suit and get in the pool to vegitate.

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I skimmed through a lot of this discussion and didnt notice anybody mention the suspension's affect on the radius of your turn. If you roll on the throttle the forks changes the bikes geometry. Longer forks tubes mean slower turning for a given lean angle. Conversly the brakes compress the front increasing the rate at which the bike turns for a given lean angle. All of which comes together somehow to explain what Keith is trying to teach us.

 

For instance, on the way in to a turn you are deaccelerating so the forks are compressed helping you tighten the line without adding lean angle. On the way out you are hard on the throttle causing the tubes to extend and widen the line. If the line is too wide you can slide yourself up on the seat and lean your chest a bit lower to put more weight up on the front to tighten the line back up without adding lean angle.

 

But I'm pretty confident the CSS guys can explain it better than I have.

 

 

Well I could be wrong but from my understanding the way the suspension is compressed has nothing to do with your turning radius what so ever. Your turning radius is determined by where the front tire is pointing regardless of how the suspension is compressed. Your lean angle is also determined by where the front tire is pointing. If the front tire has you pointed in a 1G turn that means your lean angle will be 45 degrees.

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Well I could be wrong but from my understanding the way the suspension is compressed has nothing to do with your turning radius what so ever. Your turning radius is determined by where the front tire is pointing regardless of how the suspension is compressed. Your lean angle is also determined by where the front tire is pointing. If the front tire has you pointed in a 1G turn that means your lean angle will be 45 degrees.

 

I'm not certain that you have to be at 45 degrees in order to pull 1G. I know that I can get the bike to 45 degrees going pretty slowly and not pulling anywhere near 1G. I do it all the time on turn 11 going in to the pits. Just one last knee drag to say good bye.

 

I wonder: given a really huge skid pad, say 5 miles in radius, if you went really fast, pretend we're on a light cycle, but were turning in an arc that was really wide if you could go fast enough to pull 1G with only 15 degrees of lean angle.

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I wonder: given a really huge skid pad, say 5 miles in radius, if you went really fast, pretend we're on a light cycle, but were turning in an arc that was really wide if you could go fast enough to pull 1G with only 15 degrees of lean angle.

 

Physics says that is impossible. A motorcycle uses a specific lean angle because that is the point where the cornering G and the gravity trying to pull the bike to the ground meet and balance each other out. For a 1G turn the motorcycle might be slightly off of a 45 degree lean angle depending on body position but it can't be off my much. For example if you had a cornering force of 0.5G and you were at a 45 degree lean angle the force of gravity would pull the bike to the ground because there isn't enough cornering forces to hold it up. At any decent amount of speed (I guess about 20mph+) a motorcycle's lean angle is determined by its cornering G and unless you can defy physics nothing will change that.

 

A motorcycle doesn't turn because its leaning it turns because thats where the front tire is pointing. If the front tire is making the motorcycle follow a 1G turn it will be leaning at 45 degrees and if its 2G the motorcycle will be leaning at 60 degrees. The only time you can change that is at very low speeds where your body weight can counter act it but even then the front tire will be pointing on the exact radius of the turn, if it wasn't then the front tire would need to be skidding.

 

 

 

 

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  • 1 month later...

A quick sketch might help.

 

post-15311-128296161539_thumb.jpg I think you have to double tap to see the full size image

 

This is what happens.

The only thing that can change is the speed.

The CG, and the lean angle remain constant.

 

(Airplanes work basically the same way)

 

Thanks, that makes it so much easier to understand! I always have a hard time finding the words to explain something like that. I'm guessing the graph assumes its also the same radius turn? If you took an 80mph turn at 50° lean angle it would just be a wider turn compared to 50mph.

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