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Low Sided But Not Sure Why (Track Day)


mazur
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Today was my third ever track day and things were finally coming together for me in terms of being more comfortable with my body positioning and the lean angle of the bike. I ride a SV650 for reference.


During my third session, I was increasing my lean angle still further and therefore was able to increase my overall speed, so I was feeling pretty good. Then it appears as though I took it too far. I was already in a corner and wanted to tighten up the turn with a bit more speed, so I increased my lean a touch further and the bike just fell from under me.


I am somewhat perplexed about the situation, though. Considering my bike is mostly stock with stock rear sets (just has GSXR 1000 front end and zx10 shock) I thought for sure that even if I didn't drag knee, I would at least drag hard parts before I would hit the limit of the tires. The tires are Road Attacks, which I hear is not that great of a tire, but I figured you should be able land a knee with most tires as long you aren't pushing the traction limits with excessive throttle input in a corner.


I thought about blaming a dusty track due to my slide being almost completely on my ass and my pants still look brand new (thought the leather would be torn up at least a little), but I am not sure. I'm still a motorcycling noob and I don't know how to perceive what the lean limit is. I feel as though I had to low side to be able to say "there's the limit, now I know", but that does not seem intuitive to me. There should be other signs to help you, right?


My background is in racing cars and karts so this two-wheel thing is still somewhat of a mystery to me :)

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Mazur,

 

Sorry to hear about the crash but I'm glad you're ok. Let me start by asking if you have read "A Twist of the Wrist 2"? It addresses many common rider errors that can reduce a bike's traction due to improper rider inputs (i.e. slide before hitting hard parts or even getting your knee down). Being stiff on the bars is one of several of those errors. In your case, if you were stiff/tight on one or both of the bars you will have reduced the traction of the front tire. Maybe not enough to fully CAUSE the crash but certainly enough to contribute to it.

 

As for the crash, I need a bit more info to help. First, could you tell which tire gave way... front or rear? Also, as you were adding your lean angle, were you rolling on the throttle at the same time or did you stop rolling on before you steered the bike into a steeper lean? What specifically were you doing with the throttle relative to your steering inputs in the corner?

 

Also, on what lap did it occur? Were you using tire warmers? Was the lean angle you were at when you crashed significantly more than it had been in the previous lap or two (i.e. a sudden leap in speed in that corner)?

 

Finally, have you had your suspension set up for your weight (i.e. set the sag)?

 

Cheers,

Benny

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Hey Mazur,

 

Sucks to hear about your low side. I can tell you one thing, you came to the right place with questions about cornering. The ppl here are not only the best in the business, but explain things in a way that promotes knowledge and confidence.

 

I'm assuming that since you came here, you already know about Kieth Codes book, Twist of the Wrist II. If you don't, it is pure gold for new and even experienced riders. It explains the mechanics about everything relating to riding a motorcycle effectively.

 

Good luck out there.

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Have read "A Twist of the Wrist 2"?



No, just seen the movie.



Which tire gave way... front or rear?



I am not 100% sure, but I would say it was the rear since the rear end of my bike spun out away from me in the slide.



As you were adding your lean angle, were you rolling on the throttle at the same time or did you stop rolling on before you steered the bike into a steeper lean? What specifically were you doing with the throttle relative to your steering inputs in the corner?



I am fairly certain I was rolling on.



On what lap did it occur?



It was mid session, so I was probably already at least 7 laps in.



Were you using tire warmers?



No, just using street tires, so why would I have any?



Was the lean angle you were at when you crashed significantly more than it had been in the previous lap or two (i.e. a sudden leap in speed in that corner)?



I wouldn't call it a sudden leap in speed and angle. I doubt I added more than a couple degrees.



Have you had your suspension set up for your weight (i.e. set the sag)?



Somewhat. The bike is stiffly sprung. Even with the forks at full soft I cannot reach a "proper" sag. I matched the rear sag relative to the front, so to keep a balance, but that would mean that overall the bike is stiff.





I will add one more thing. My friend that was with me that day said that in the same corner, he noticed a significant crack that ran concentric with turn and that when he went over it he felt his rear end slide out a bit but was able to ride through it without issue (as far as riding he s more experienced and had significantly better rubber as well). So this could have also been a contributor, as I also widened up my line to set up for a later apex. This could have put me in a bad position in relation to that crack in the road where it would not have been a problem before.

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As you were adding your lean angle, were you rolling on the throttle at the same time or did you stop rolling on before you steered the bike into a steeper lean? What specifically were you doing with the throttle relative to your steering inputs in the corner?

I am fairly certain I was rolling on.

 

This might be the issue, then. The coaches at the school will call you off-track if they see you doing this. They also mention this being an issue in the movie.

 

I'm pretty cognizant of this because in my first lap at CSS, I got called off for doing exactly this. It's apparently a huge source of crashes where the rear lets go. There's just not enough traction to turn and roll on. Set lean angle, and then roll on.

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Agree with fieryrobot, on a 1000cc on street tires you can lose the rear by leaning and rolling gas at the same time.

 

Lots of cars videos on this track. Grip is probably not as good as a dedicated motorcycles track. I can't locate turn 10, can you check this video and give us the minute/second showing the turn?

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Have read "A Twist of the Wrist 2"?

No, just seen the movie.

Close enough. -B

Which tire gave way... front or rear?

I am not 100% sure, but I would say it was the rear since the rear end of my bike spun out away from me in the slide.

If the rear came around as you said then I agree it was most likely the rear and that makes sense with what you say next. -B

As you were adding your lean angle, were you rolling on the throttle at the same time or did you stop rolling on before you steered the bike into a steeper lean? What specifically were you doing with the throttle relative to your steering inputs in the corner?

I am fairly certain I was rolling on.

I think we have the most likely reason here. Adding throttle and lean angle at the same time is the number one reason for track crashes as FieryRobot alluded to. We will instantly pull in students at the school for doing so. Doing either one alone requires the rear tire to deliver more traction and the contact patch increases in size to meet the demand (like pressing a balloon onto a table). However when you do both at the same time, you effectively demand that traction faster than the tire can grow causing a loss of traction. Even sophisticated traction control systems can't save you. If you have to add lean angle in a corner, you MUST at least stop adding throttle. Rolling out of it is also acceptable. -B

On what lap did it occur?

It was mid session, so I was probably already at least 7 laps in.

Was checking to see if your tires were warm. -B

Were you using tire warmers?

No, just using street tires, so why would I have any?

Was the lean angle you were at when you crashed significantly more than it had been in the previous lap or two (i.e. a sudden leap in speed in that corner)?

I wouldn't call it a sudden leap in speed and angle. I doubt I added more than a couple degrees.

Was making sure you didn't put it on a cold edge of the tire. -B

Have you had your suspension set up for your weight (i.e. set the sag)?

Somewhat. The bike is stiffly sprung. Even with the forks at full soft I cannot reach a "proper" sag. I matched the rear sag relative to the front, so to keep a balance, but that would mean that overall the bike is stiff.

I will add one more thing. My friend that was with me that day said that in the same corner, he noticed a significant crack that ran concentric with turn and that when he went over it he felt his rear end slide out a bit but was able to ride through it without issue (as far as riding he s more experienced and had significantly better rubber as well). So this could have also been a contributor, as I also widened up my line to set up for a later apex. This could have put me in a bad position in relation to that crack in the road where it would not have been a problem before.

This can further reduce traction but almost certainly didn't cause the crash. I recommend having your forks re-sprung for your weight so you can set the proper sag. However, if you weren't sliding before and your pace didn't increase suddenly then it's not yet a significant issue for you. -B

Benny

 

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Agree with fieryrobot, on a 1000cc on street tires you can lose the rear by leaning and rolling gas at the same time.

Lots of cars videos on this track. Grip is probably not as good as a dedicated motorcycles track. I can't locate turn 10, can you check this video and give us the minute/second showing the turn?

 

In that video, from the camera's POV, I would have went down at 1:16, but taking a wider line.

 

For a better perspective, check out my video from my first track event where I took a similar line. At 00:52 is where I went down.

 

Thanks BENHAMF15, that helps a lot.

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Very interested in this topic. I will not offer advice because there are others here much better equipped to do so. I just wanted to mention that I had a very similar type of crash at a very similar stage of development as a track rider. Already in the corner, just decided to crank it over more, rear end went away. I was nowhere near the lean angles I now achieve on the same bike with similar tires. The major changes I made in my riding since then were: 1. getting WAY more comfortable and therefore relaxed on the bars while leaned over, and 2. setting my lean angle with one quick steering input then not adding more lean while in the corner and rolling on. If I get it wrong and don't think I will make the exit I will just hold steady throttle (which actually produces deceleration) a bit longer before rolling on. Rolling on + adding lean = bad juju.

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"Thanks BENHAMF15, that helps a lot."

 

You're welcome! I'm glad you found it helpful. Any chance you can make it to a school? I think it would help you a lot, especially if you're going to be doing regular track days.

 

Benny

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Very interested in this topic. I will not offer advice because there are others here much better equipped to do so. I just wanted to mention that I had a very similar type of crash at a very similar stage of development as a track rider. Already in the corner, just decided to crank it over more, rear end went away. I was nowhere near the lean angles I now achieve on the same bike with similar tires. The major changes I made in my riding since then were: 1. getting WAY more comfortable and therefore relaxed on the bars while leaned over, and 2. setting my lean angle with one quick steering input then not adding more lean while in the corner and rolling on. If I get it wrong and don't think I will make the exit I will just hold steady throttle (which actually produces deceleration) a bit longer before rolling on. Rolling on + adding lean = bad juju.

 

Me, too, almost exactly the same thing happened to me at about that same stage in my riding - my crash and the whole process and list of changes I went through were just like YellowDuck describes above. :) I ended up attributing my crash to the mid-corner steering adjustment, combined with continuing to roll on the throttle, and now I don't do that any more - if I need to tighten my line in a little in a corner I do it with hook-turn or by using the throttle (stopping or reducing my roll-on to let the bike slow a little and tighten the arc). I do not make mid-corner steering change. (Keep in mind this is not the same situation as a double apex corner, where you actually do have a second turn point for steering the bike, that is a different situation.)

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Bouncy before that left apex. So acceleration + leaning + all those cracks might have make it. Did you want to increase the lean angle at that point to straight up the next right corner?

Nice flip at the end, I hate cones too :)

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Bouncy before that left apex. So acceleration + leaning + all those cracks might have make it. Did you want to increase the lean angle at that point to straight up the next right corner?

Nice flip at the end, I hate cones too :)

 

Not the cones fault :)

 

I for some reason second guessed myself on that corner that lap and fixated on where I didn't want to go. Plus, I was on the front brake when I hit the dirt :P

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............. I was increasing my lean angle still further and therefore was able to increase my overall speed .................. I was already in a corner and wanted to tighten up the turn with a bit more speed, so I increased my lean a touch further and the bike just fell from under me.
I am somewhat perplexed about the situation, though. .............

 

It may seem evident, but I would like clarifying a little about the lean angle.

 

The bike must be leaned to be in balance, just like it must be kept vertical when tracking a straight line.

 

There is only one possible angle for each combination of speed and radius of turn.

 

Those two things rule and the lean angle follows.

 

You go over the same line for a curve: less speed requires less lean angle; more speed requires more lean angle.

 

You travel at a constant speed: more radius turn (less tight curve) requires less lean angle; less radius turn (more tight curve) requires more lean angle.

 

When you are leaned, in balance, describing a circle, there is only one way to go faster: opening the throttle more.

As speed increases, the lean angle will increase in order for the bike to remain in balance.

 

If you force a bigger lean angle via countersteering, you can only keep balance if you tighten the turn (reduce the radius).

Otherwise, you just throw the bike out of balance.

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............. I was increasing my lean angle still further and therefore was able to increase my overall speed .................. I was already in a corner and wanted to tighten up the turn with a bit more speed, so I increased my lean a touch further and the bike just fell from under me.
I am somewhat perplexed about the situation, though. .............

 

It may seem evident, but I would like clarifying a little about the lean angle.

 

The bike must be leaned to be in balance, just like it must be kept vertical when tracking a straight line.

 

There is only one possible angle for each combination of speed and radius of turn.

 

Those two things rule and the lean angle follows.

 

You go over the same line for a curve: less speed requires less lean angle; more speed requires more lean angle.

 

You travel at a constant speed: more radius turn (less tight curve) requires less lean angle; less radius turn (more tight curve) requires more lean angle.

 

When you are leaned, in balance, describing a circle, there is only one way to go faster: opening the throttle more.

As speed increases, the lean angle will increase in order for the bike to remain in balance.

 

If you force a bigger lean angle via countersteering, you can only keep balance if you tighten the turn (reduce the radius).

Otherwise, you just throw the bike out of balance.

 

 

I'm a little confused by this.

 

If you accelerate mid turn, the bike will come up if you don't do anything to stop it, right? The shear force on the front tire from the ground, due to the acceleration of the rear tire, pushes on the front contact patch and does the same thing (creates the same resistance at the contact patch) as countersteering the bike up does -- at least, that's my understanding.

 

If that's the case, then if you accelerate, the only way to keep the same radius is to "force" a bigger lean angle by countersteering. Right?

 

Also, by bring the bike out of "balance", do you mean away from the point that it is turning without you needing to maintain pressure on the bar? (As if it is "balanced", once you initiate the turn, you shouldn't have to maintain any pressure to continue at that radius.)

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Mazur,

 

I also don't have anything useful to add to the quest of "why" it happened. I will however point out that the fact that since you are interested in the "why" already put's you ahead of many riders out there. Crashes always suck but you can turn them into a learning experience as you are doing.

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So reading over this topic leads me to a question. It's been stated a couple of times that adding lean + throttle roll on is bad juju and I agree with that. I wonder however how weight and a geometry shift might affect such a scenerio? The hook turn drill that the superbike school teaches could be used to add a geometry change and weight shift to tighten the line. Would that help or hurt a going wide situation while on the power?

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So reading over this topic leads me to a question. It's been stated a couple of times that adding lean + throttle roll on is bad juju and I agree with that. I wonder however how weight and a geometry shift might affect such a scenerio? The hook turn drill that the superbike school teaches could be used to add a geometry change and weight shift to tighten the line. Would that help or hurt a going wide situation while on the power?

Hook turn helps to tighten the line by shifting weight forward and inside, which helps compress the forks, changing the geometry and tightening the line without having to add more lean. However, rolling on the throttle strongly creates the opposite effect, shifting weight rearward and increasing speed which will widen your line. A strong roll-on on a bike with decent horsepower could overcome the effect of the hook turn position. Hook turn is most effective when used before you start driving out of a corner, or can be used in combination with going 'flat' on the throttle (pausing your roll-on) briefly, which you might do in the middle of a double apex corner.

 

To answer your question, it wouldn't hurt, it would help, but the effect of accelerating the bike would be much stronger, so it likely wouldn't help dramatically. It's a much more effective tool when used at the beginnning of a turn.

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So reading over this topic leads me to a question. It's been stated a couple of times that adding lean + throttle roll on is bad juju and I agree with that. I wonder however how weight and a geometry shift might affect such a scenerio? The hook turn drill that the superbike school teaches could be used to add a geometry change and weight shift to tighten the line. Would that help or hurt a going wide situation while on the power?

Hook turn helps to tighten the line by shifting weight forward and inside, which helps compress the forks, changing the geometry and tightening the line without having to add more lean. However, rolling on the throttle strongly creates the opposite effect, shifting weight rearward and increasing speed which will widen your line. A strong roll-on on a bike with decent horsepower could overcome the effect of the hook turn position. Hook turn is most effective when used before you start driving out of a corner, or can be used in combination with going 'flat' on the throttle (pausing your roll-on) briefly, which you might do in the middle of a double apex corner.

 

To answer your question, it wouldn't hurt, it would help, but the effect of accelerating the bike would be much stronger, so it likely wouldn't help dramatically. It's a much more effective tool when used at the beginnning of a turn.

 

 

Thanks for the detail. That's VERY helpful and also touches on "why" bikes run wide which I never really thought about before now. :)

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I'm a little confused by this.

 

If you accelerate mid turn, the bike will come up if you don't do anything to stop it, right? The shear force on the front tire from the ground, due to the acceleration of the rear tire, pushes on the front contact patch and does the same thing (creates the same resistance at the contact patch) as countersteering the bike up does -- at least, that's my understanding.

 

If that's the case, then if you accelerate, the only way to keep the same radius is to "force" a bigger lean angle by countersteering. Right?

 

Also, by bring the bike out of "balance", do you mean away from the point that it is turning without you needing to maintain pressure on the bar? (As if it is "balanced", once you initiate the turn, you shouldn't have to maintain any pressure to continue at that radius.)

 

Asterix,

 

I wanted to address this as it is a common misconception.

 

How could accelerating "push" the front contact patch. Is there more or less weight on that front contact patch when you're accelerating? If you say less, why would that put more force on it to cause a steering input that brings the bike upright?

 

The bottom line is that accelerating will not change your lean angle, only a steering input will. Keith addresses this in his book but I don't have it handy to give you the chapter number, but as I recall it is called "Steer With the Rear" or something along those lines. However, going faster with the same lean angle will affect your line. So the question to you is: how will that affect your line... will it be tighter or wider as a result? Could going wider be perceived as the bike "coming up" out of the corner?

 

Benny

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I'm a little confused by this.

 

If you accelerate mid turn, the bike will come up if you don't do anything to stop it, right? The shear force on the front tire from the ground, due to the acceleration of the rear tire, pushes on the front contact patch and does the same thing (creates the same resistance at the contact patch) as countersteering the bike up does -- at least, that's my understanding.

 

If that's the case, then if you accelerate, the only way to keep the same radius is to "force" a bigger lean angle by countersteering. Right?

 

Also, by bring the bike out of "balance", do you mean away from the point that it is turning without you needing to maintain pressure on the bar? (As if it is "balanced", once you initiate the turn, you shouldn't have to maintain any pressure to continue at that radius.)

 

Asterix,

 

I wanted to address this as it is a common misconception.

 

How could accelerating "push" the front contact patch. Is there more or less weight on that front contact patch when you're accelerating? If you say less, why would that put more force on it to cause a steering input that brings the bike upright?

 

The bottom line is that accelerating will not change your lean angle, only a steering input will. Keith addresses this in his book but I don't have it handy to give you the chapter number, but as I recall it is called "Steer With the Rear" or something along those lines. However, going faster with the same lean angle will affect your line. So the question to you is: how will that affect your line... will it be tighter or wider as a result? Could going wider be perceived as the bike "coming up" out of the corner?

 

Benny

 

 

Well, when you accelerate, the rear wheel is pushing the bike forward. If you are also turning, your front wheel is pointed in some direction that isn't completely inline with the rear wheel, thus, the force being generated by the rear wheel is different from the front wheel's rotation. From what I can tell, this means that the front wheel will be rotating, say 5º to the left of the direction that the rear wheel is rotating, and there will be a shear force from the ground pushing against the front contact patch (inline with the rear wheel) which will be trying to push the front wheel back inline with the rear wheel---basically the same thing that happens when you brake in a turn with the contact patch plowing (shown in the TotW II video). I understand that weight shifts back when you accelerate, but the contact patch is still touching the ground, so there's still some plowing---wouldn't that have the same sort of effect with acceleration?

 

 

I might be misunderstanding something with the physics here though. If lean angle doesn't change with acceleration, what am I missing/misunderstanding?

 

Regarding the same lean angle with more speed affecting your line, I agree that your line will have to widen so that the force of gravity and centrifugal force cancel out. But, how can your line widen without some sort of steering input? If the tires are at the same angle with the ground, and the front wheel has the same amount of "turn", and you are accelerating, the bike would end up out of balance and "fall" out of the turn (basically topple over to the outside), rather than widening its line, unless the tires start sliding.

 

It seems that my explanation above with the plowing would answer this; you accelerate, the plowing at the front wheel countersteers the bike up, decreasing lean angle, and widening the turn. To keep the same radius, you counter the plowing force (by countersteering), and increase lean angle, keeping the bike in an equilibrium state. No?

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Asterix,

 

questions for ya,

 

Is it possible to Wheelie the bike while still carrying lean angle ??

 

If a combination of speed and lean angle results in a mathematical radius, when one remains constant and the other increases what must happen to the radius ?

 

the centripetal force being applied to the front tire by the road surface is applied in what axis of the bike ?

 

the deceleration force being applied to the front tire is in what axis of the bike ?

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