Motorcycle Dynamics - Bad info here

[ReconRat]

This guy doesn't have a clue what he's talking about. And he's running a motorcycle safety website.

...If you lock your rear brake while traveling at 100 MPH your bike will fall over...

I wonder if he's ever tried it. Reminds me of the skit on The Simpsons where the SUVs try to make it around a freeway corner and they all scream and fall over.

link: Speed Does NOT provide stability

the directional stability that is claimed does exist, but it isn't much more than the rear wheel following the front wheel. Which is good, of course. An easy way to defeat the claim of this being the primary cause of stability, is to question why stability works when going over a jump, in the air, and no longer in contact with the ground.

I think he's ignoring what direction the front wheel is aimed at when the weight is transferred forward under hard braking. That would fall down if not in the line of momentum and motion. Aim correctly and lock the rear wheel and a rear skid would result with risk of low or high side fall. But it's not mandatory. Advanced riders know how to use a rear wheel skid to change direction quickly. Granted, not always successfully.

Gyroscopics play no role in maintaining your bike's upright position

Ok, how does he explain the new generation of urban motorcycles that have a pair of gyroscopes in their belly? They stand up on their own and move with no help. Some of us have seen the videos of the gyro bike bouncing off a collision and never falling down.

I'm not going to fault him for championing motorcycle safety, he's put in a lot of effort. But the physics of his analysis of dynamics leaves some room for work.

[ReconRat]

I've read some of the other motorcycle tips he has, and most are pretty good.

He got the shift body weight TOWARD a scraping peg correct. And a lot of others.

[Moto-Brian]

I think he isn't far off, but not explaining it well.

There is a gyroscopic effect that occurs. The gyroscopic effect wants the bike to stand up straight while leaned over. Without your (rider) control, the bike will tend to stand up. I think that is the idea you are referring with the belly pan gyros in some bikes... The effect is always at hand and wanting to be working against the rider.

As for trail, he is correct. Kinda... He is saying that the front end's trail is what determines stability. He is correct. Get it wrong and the bars slap like a pissed off girlfriend. Get it right and the bike is stable. But, trail alone isn't the end all. The rear DOES cause issue with handling. You can add or reduce trail with rear ride height. He's trying to say everything is related to the front only and not the rear. Steering or maintaining that angle of trajectory can be done via the rear wheel.

At VMD this year, I was having what I felt was rear wheel traction issues. I took away preload. The bike and the chassis setup I run with had been greatly changed and the handling was changed for the worse.

Before, the rear did spin and I was able to maintain the line and exit on drive. While it was spinning, it was still gripping to a point for my riding style, was working. When I took away preload to try and get a bit more squat and "traction" from hook up, I did just that. However, the bike would want to stand up and run wide. It was understeering badly. It was leaving blackies on drive and wanting the bike to stand up quickly before finishing the turn. Therefore, it kind of goes against what this guy is saying. You CAN steer with the rear and you can also have TOO MUCH steering with the rear.

Point is that what he is saying is mixed up and using several different ideas rolled into one. This is the issue with these so called "experts" that put info out to the general public. It's too easy and often what really gets me pissed off, a newbie rider that is VERY green takes these bits of info and gets all kinds of confused or I see people that are teaching or instructing that take the info and spread it as if it is accurate. Our issues are bad enough in just getting riders to ride in a manner that is safe and advancing. Let alone giving them info that if applied to their bikes, can cause serious issues and put them further back of the line...

[Moto-Brian]

I've read some of the other motorcycle tips he has, and most are pretty good.

He got the shift body weight TOWARD a scraping peg correct. And a lot of others.

You actually weigh the outside pegs at lean to stabilize the machine. Don't weight the inside or dragging peg... You are essentially pushing the bike outwards and away from yourself if you weigh or push on the scrapping peg...

[ReconRat]

You actually weigh the outside pegs at lean to stabilize the machine. Don't weight the inside or dragging peg... You are essentially pushing the bike outwards and away from yourself if you weigh or push on the scrapping peg...

Yes, he got that part right also. I think he just wants people to avoid "jerking their body away". Which doesn't help the situation. Pushing outside and leaning body weight toward the ground will lift the bike, without disturbing line. Maybe.

edit: Just read your longer post. It helps having your experience here on the forum.

I'm still thrashing with "wanting the bike to stand up quickly before finishing the turn".

It's not too bad, but I'll fix it eventually. It's a stock bike and suspension after all.

And my front fluids/springs are getting to be hosed, it's "topping out" with a clack over speed bumps.

The joys of a bike growing old (without maintenance).

Edited January 6, 2013 by ReconRat

[Moto-Brian]

Yes, he got that part right also. I think he just wants people to avoid "jerking their body away". Which doesn't help the situation. Pushing outside and leaning body weight toward the ground will lift the bike, without disturbing line. Maybe.

edit: Just read your longer post. It helps having your experience here on the forum.

I'm still thrashing with "wanting the bike to stand up quickly before finishing the turn".

It's not too bad, but I'll fix it eventually. It's a stock bike and suspension after all.

And my front fluids/springs are getting to be hosed, it's "topping out" with a clack over speed bumps.

The joys of a bike growing old (without maintenance).

It's a lot about geometry also. You can get great handling from raising and lowering the forks and rear ride height depending on the year of bike and setup, etc. Adding trail to these newer bikes seems to be the key for some reason. Not sure why the factories do not have the trail numbers closer where we race with, but that seems to be the dealio.

[vf1000ride]

Sorry, I believe very little of that article. Locking a back tire at 100+ can be ridden out. I have done it from the 90mph range under panic braking and certainly didn't crash. Now granted I recognized the locked tire and didn't try to ride it all the way to a stop but it certainly didn't throw me in the street either. I also feel the explanation of the stability coming from steering head angles, rake and trail to be over-rated also. All of those things are extremely important with both tires on the ground and with full traction but how do you explain a bikes stability in a wheelie or stoppie when all that fancy geometry is tossed out the window. Here's a perfect example of a dude riding out a stoppie from 130+ mph.

http://www.youtube.com/watch?v=AVSn4FbQiTA

I don't see his bike immediately crashing when the back tire lifted off. It didn't crash as he slowed down with only the front wheel. Heck trail and rake went out the window as soon as the frame rotates around the axis of the front axle and even then it didn't crash. So what does our famous "recognized expert witness in the fields of Motorcycle Safety/Dynamics." have to say about that. If it's not rear wheel traction, it's not the front wheels engineered steering ability. What keeps the bike stable? God forbid it would be vehicle speed and gyroscopic stability.

[Moto-Brian]

Uh, not sure you're grasping the idea even if he's somewhat saying it wrong. He's talking about a bike that is turning and the process it goes through while handling turns, etc.

The example you are giving has nothing to do with the idea. Wheelies and stoppies don't work with a whole lot that road race or track day bikes work with. His concept is the bike will crash while leaned over and rear brake stomped. Straight up and down is not a trail or steering angle issue.

[vf1000ride]

Uh, not sure you're grasping the idea even if he's somewhat saying it wrong. He's talking about a bike that is turning and the process it goes through while handling turns, etc.

That just shows how poorly written that article is. I have reread it and still don't get your impression of the situation from his writing style. If you want to limit stability talks to the bikes stability only when cornering, sure his statements can apply. He is claiming though, with no other extraneous text that "If you lock your rear brake while traveling at 100 MPH your bike will fall over."

I am saying that in a straight line that is a false statement. A skilled rider can lock the back tire and ride it to a safe stop without crashing if it is done while the bike is upright. That is why I posted the video of the stoppie. It shows that the rear tire can have no grip on the road and even by radically changing steering angle and even negating his restoring force theory that a motorcycle can remain stable from well over 100mph to almost a dead stop.

His second to last paragraph continues to confuse the issue of if he means the bike is upright or leaning from my point of view.

1st sentence He claims that once the wheel is locked it will cause the bike to fall over in a matter of seconds. That makes it sound like you could have been cornering and that is a fair statement.

The very next sentence then goes on to say that road anomalies will begin the rear end yawing and the bike will slide out from under you. This makes it sound like you where upright. If you were corning at this point you don't need road anomalies to cause the crash, it's gonna happen regardless of surface conditions. Why even bring road conditions into a statement like that if it was meant to imply that you were corning. Road conditions are a moot point with a locked rear wheel for all situations other than fully upright.

The entire article is written on a level I would have expected an internet forum troll to write. It contains too little info to make a fair judgement of the situation and then makes bold and radical statement based on a situation that was not properly defined. Due to poor wording it seems that it contradicts itself and it tries to ignore or dismiss several aspects of the dynamics that make motorcycles functional. He may make good points in some of his other articles but with how poorly worded this one is I have no want to read any of the others.

[Moto-Brian]

That just shows how poorly written that article is. I have reread it and still don't get your impression of the situation from his writing style. If you want to limit stability talks to the bikes stability only when cornering, sure his statements can apply. He is claiming though, with no other extraneous text that "If you lock your rear brake while traveling at 100 MPH your bike will fall over."

I am saying that in a straight line that is a false statement. A skilled rider can lock the back tire and ride it to a safe stop without crashing if it is done while the bike is upright. That is why I posted the video of the stoppie. It shows that the rear tire can have no grip on the road and even by radically changing steering angle and even negating his restoring force theory that a motorcycle can remain stable from well over 100mph to almost a dead stop.

His second to last paragraph continues to confuse the issue of if he means the bike is upright or leaning from my point of view.

1st sentence He claims that once the wheel is locked it will cause the bike to fall over in a matter of seconds. That makes it sound like you could have been cornering and that is a fair statement.

The very next sentence then goes on to say that road anomalies will begin the rear end yawing and the bike will slide out from under you. This makes it sound like you where upright. If you were corning at this point you don't need road anomalies to cause the crash, it's gonna happen regardless of surface conditions. Why even bring road conditions into a statement like that if it was meant to imply that you were corning. Road conditions are a moot point with a locked rear wheel for all situations other than fully upright.

The entire article is written on a level I would have expected an internet forum troll to write. It contains too little info to make a fair judgement of the situation and then makes bold and radical statement based on a situation that was not properly defined. Due to poor wording it seems that it contradicts itself and it tries to ignore or dismiss several aspects of the dynamics that make motorcycles functional. He may make good points in some of his other articles but with how poorly worded this one is I have no want to read any of the others.

A skilled rider can also save a front end tuck with their knee. Doesn't mean everyone can do it...

I am not trying to defend the guy as I agree his info is sketchy at best. But, he is clearly talking about a bike NOT IN A STRAIGHT LINE as he put in bold. He is discussing the effects of locking the brakes at 100mph while leaned over. He is talking gyroscopic things and rake/trail of a bike and how it pertains to handling...

Your example is fine, but also realize that stunters put in HEAVY weight oil and crank steering dampers to full tilt. Ever tried to steer a stunt bike? They arent sloppy like my bike with next to zero steering damper input...

Point is that if you did that stoppie on my race bike with my damper set to almost zero, the bike will get sloppy and most likely cause a crash. You can setup almost anything in the world to go against a statement made for the overall general out there.

Road characteristics CAN play an issue into the way a bike reacts while leaned over. Going over ripples in the pavement, etc can cause feedback that can change the way a chassis reacts. So, that is not false either...

Again, not defending the guy, but to call him a troll is somewhat unfair. I would say he understands what a bike does and is trying to state things for others to understand. I unfortunately think he expresses them poorly. Maybe not in a totally wrong fashion as he does have some valid points, but it is somewhat confusing obviously, but I understand what he is trying to say.

I think you might want to take what his point is and try and understand what he is TRYING to convey and then respond. Otherwise, it looks just as bad to make fun of the guy when you aren't very accurate in your own points of response...

[vf1000ride]

Ok, so we obviously read his writing style completely differently. This was my main complaint at the end of my reply. His article is so poorly written that two people who both ride and understand motorcycle physics in our own ways come to 2 completely different viewpoints as too what he is trying to imply. I would agree with probably 90% of his statements if somewhere in his writing he would put an obvious statement that the article and his theory is based solely on the dynamics of a cornering bike. I don't feel he makes that clear and his writing can be construed as a train wreck of theory for upright riding mixed with the theory of cornering.

Again, not defending the guy, but to call him a troll is somewhat unfair.

I do maintain my statement though about the internet troll bit. The article is written so poorly I would have expected something like that from a troll and not from a motorcycle safety expert. Look over the last page and a half of posts on our forum. The viewpoints are very mixed with nobody agreeing. Is that not what would constitute stirring the shit or trolling on this forum in any other situation? It has caused the two of us to get into a pissing match over who understands his writing style better and it is for no good reason. I have never felt the need before this to question anything you have posted and probably never will in the future either. If the person that wrote the article was on the forum, he would have been called out to explain the meaning of his article and to justify bold statements about motorcycle physics, that depending on the situation, few people can agree with.

[CBBaron]

I think he isn't far off, but not explaining it well.

There is a gyroscopic effect that occurs. The gyroscopic effect wants the bike to stand up straight while leaned over. Without your (rider) control, the bike will tend to stand up. I think that is the idea you are referring with the belly pan gyros in some bikes... The effect is always at hand and wanting to be working against the rider.

As for trail, he is correct. Kinda... He is saying that the front end's trail is what determines stability. He is correct. Get it wrong and the bars slap like a pissed off girlfriend. Get it right and the bike is stable. But, trail alone isn't the end all. The rear DOES cause issue with handling. You can add or reduce trail with rear ride height. He's trying to say everything is related to the front only and not the rear. Steering or maintaining that angle of trajectory can be done via the rear wheel.

The steering geometry is primarily responsible for the bike wanting to stand up in a turn, not gyroscopic effect. Gyro bikes use different mechanisms to make the bike stay upright. However with out controls on the bike will not lean in a turn. If you the steering geometry wrong the bike will dive into a turn and keep turning sharper unless you muscle it out.

Trail is a function of the frontend. Lowering the rear does change trail but only because that changes angles in the front end. So that is just a matter of semantics. It is a front end function as long as you keep the bike level.

Many times when trying to dumb down an explanation to a level that is useful for the average user, the explanation starts to not make sense when examined in detail. This happens with most complex concepts.

Craig

[Moto-Brian]

The steering geometry is primarily responsible for the bike wanting to stand up in a turn, not gyroscopic effect. Gyro bikes use different mechanisms to make the bike stay upright. However with out controls on the bike will not lean in a turn. If you the steering geometry wrong the bike will dive into a turn and keep turning sharper unless you muscle it out.

Trail is a function of the frontend. Lowering the rear does change trail but only because that changes angles in the front end. So that is just a matter of semantics. It is a front end function as long as you keep the bike level.

Many times when trying to dumb down an explanation to a level that is useful for the average user, the explanation starts to not make sense when examined in detail. This happens with most complex concepts.

Craig

First of all, all motorcycles create a gyroscopic effect. The bike does NOT want to stay on it's side, my friend. It wants to naturally stand up. I didn't say they had "gryroscopes" on the bikes themselves. I was referring that they create a gyroscopic effect. Which is true.

Yes, the trail is a front end deal. But, you can effect trail greatly with rear end ride height. The front and rear work together. It has to be understood that they are separate tuning aspects and need to be addressed and looked at. Otherwise, there wouldn't be any need to adjust the rear end at all to assist in handling.

OK, (for those not sure) basics of motorcycle chassis setup. Trail is the line front a horizontal center point of the axle and the line that represents the fork center of the triple following to the ground. Follows the fork parallel... IF you lower the rear of the motorcycle, you then create a difference in trail. The axle centerline doesn't change. You lowering the rear will extend trail as the angle of the forks at the center of the triple clamp changes.

At times, we will drop the rear and raise the front end to add trail. This stabilizes the bike at different areas. It can also help assist in quick transitions left to right. As the bike is on it's ear, we can move the bike while leaned over. If the front is lowered too much, yes, the bike will transition quickly left to right and adding load on the front is an old school way of doing this. But, the stability suffers and moving the bike while leaned over is tougher.

Motorcycles need to be tuned in harmony with the front and rear. Chatter, stability, reaction while leaned over, etc are all things that can be tuned for with the rear and front. Doing one alone can greatly hurt a setup and not usually be a single idea. Now, you can fine tune with just the front or rear, but the idea is that when you find the sweet spot at whatever track or environment you are in, typically it is good with only minor tweeks to get it finely tuned for even better performance. The track never stays the same and the street for sure is never the same mile to mile...

I think we all get it. I just think it is now getting to a point we are arguing that the guy is bad or horrible. I say let's be done with it...

[Moto-Brian]

But, the author is wrong. Speed will create stability and it is due to the gyroscopic effect. Again, the wheels cause this and will stabilize the bike at speed. While leaned over, the effect causes the bike to want to stand up...

[ridein]

:)If you are so sure you won't go down hitting the back brake only at 100 MPH,There only one way to find out go do it......He is 100% right you are going down...I bet no one wants to go try it...

[Moto-Brian]

:)If you are so sure you won't go down hitting the back brake only at 100 MPH,There only one way to find out go do it......He is 100% right you are going down...I bet no one wants to go try it...

I had my rear wheel lock at triple digit speeds about at the kink at Mid-O when I spun a rod... I didn't crash... Of course, I pulled the clutch in and free rolled a good bit. I also had a rear lock from a chain that broke on a supermoto off the back straight at CRP which was probably about 60-ish at least. That I couldn't clutch.

You aren't going to go down if you understand how to handle the situation...