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Shuttering During Transition.


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Last weekend we were watching GP racing and there was a brand new rider with us asking A LOT of questions. I was happy to answer them and could simplify most things enough for her to understand. I used to teach soldiers many different things and now teach medicine to nurses and patients, so I can really break things down for different levels of people. During the race, Elias did this:

 

 

 

 

She asked why the bike shook like that. We figured it was his gripping the bike and transferring the shuttering throughout because of all the power. I couldn't figure out why a GP rider would have this problem, though.

 

Now, the day before this I found a bunch of articles written by Keith when I archived them on Motorcyclist.com in my search for more to study. I hadn't read them yet, and there are just SO MANY things in TOTW 2 that you can read, but can't piece together until you SEE or FEEL them happen, then re-read the book (this is exactly why I now suggest to everyone who has TOTW 2 to re-read it after every trackday so they can piece together what's in the book by their experiences thus increasing their knowledge) and have it put in words along with an experience to match it to. Until I was reading while I was exercising this morning, I didn't even know it was IN TOTW 2. I hadn't experienced it visually or physically, so it didn't make the connection. Another odd way of things coming together. I actually know now why it's called the cornering bible. It is incredibly accurate and thorough.

 

Anyway, the next day I started reading through the articles I'd found in Motorcyclist, and came across the real explanation why Elias got shaken so badly during his transition in the corner. I read "Use And Abuse Of Motorcycle Bars" from the August 2010 issue. While It had other interesting things, what pertains to Elias' error was this:

 

"As we transition from one side to the other, there is yet another complication: The bike becomes light as it swings over the top of its roll arc. Exaggerated inputs at this point are notorious for causing pronounced twitching or headshake, especially when the bike is under acceleration. Should a wheelie happen in this scenario, any fork rotation can bring about serious effects like a full-on tank-slapper all the way to the front contact patch auguring in and flicking the back around: the dreaded high-side.

The usual solutions for any of these distracting effects are to slow down or apply more effort to the situation, but the conflicting nature of the forces negates applying more ergs of energy as a viable solution. Better timing of the control inputs can improve it. Moving over in the seat prior to the next steering change can eliminate the rotational torque happening simultaneously with the steering inputs. That puts the rider in a better position to steer the bike. Gear changes can be done earlier or later. Using tank-grip pads to help maintain a stable position on the bike can offer some mechanical improvement.

 

 

In the end, though, each rider has an optimum position on the bike for making these inputs without the strain and pain. Correct positioning of the controls-peg height fore, aft and vertical; seat height, tilt and length; bar rotation in and out-is essential. Spending money on adjustable rearsets can make a world of difference in fit.

 

 

While the mechanical aspects may all be set correctly for the rider, it is no guarantee he'll be purposeful and in control with his inputs. The right timing and positioning isn't something most riders achieve in a single day."

 

Then today while I was reading TOTW 2 again, I came across this. It's in regards to a single turn:

 

"As an example, most novice knee draggers try to hang off and steer at the same moment. This is a big mistake as it only serves to make the bike wiggle at their turn-in point. One of the reasons the hanging off riding style works so well is that your body is already in a low and stable position on the bike when you flick it into the corner."

 

That's for a single turn, but it gives you an idea of why the bike shakes in the first place. Just turning the bike is going to decrease the weight of it while you're leaning. It's not significant unless you're turning the bike too fast OR you remove a weight from it WHILE YOU'RE TURNING IT, like shifting your weight while making that turn input.

 

Then it goes on to this:

 

"In the esses, where one turn immediately follows the other, you time your steering so it comes right after you settle to the seat. The mistake is trying to turn while you're moving from one side to the other side of the bike and aren't firmly and comfortably anchored to it. There's almost no way to completely eliminate quick-turn transition wiggles, but trying to steer while you're off the seat adds unnecessary input into the bars because they become your primary pivot point.

Trying to steer and hang off at the same time and trying to steer while moving from one side of the bike to the other are just two of the ways riders contribute fuel for their survival reaction fires and upset the bike in the process."

The fix for this, as a side-note, is:

"In esses, you're always trying it quicker. But start slower and smother so you finally get to turning it when your weight hits the seat." (It's because the added "dropping" of the weight essentially creates more for a brief moment)

I figured it out without figuring it out some time ago. I was playing with a pencil and had it sideways in the palm of my hand with the eraser side down. I flicked it so it arched over and into my other hand, which was laying on the other side, palm up, to catch it. I found a speed that would allow me to flick it just enough that it would fall to the other side without the eraser on the ground sliding across the table (that would be traction). I was able to speed up flicking the pencil from one open palm to the other, making the eraser slide a little or a lot, whichever I chose. I found the "traction limits" of a pencils eraser. It becomes much harder, though, to be stable when I start flicking the pencil when it has more lean.

Weight comes into effect when dealing with traction limits, I figured, because if the pencil were heavier I'd need more force to make the eraser slide (lose traction) going side to side. That makes it more stable. A certain weight would be ideal. Too much added weight to the "ideal weight" of the pencil would be too cumbersome and difficult to switch from one side to the other and too light would make it hard to control and maintain eraser traction. Also, if I put a weight on the writing side of the pencil, it would need even more of a push for the eraser to lose traction (it's more stable). BUT, if a weight were attached to the top of the pencil (the pencil "rider"), the more ginger I'd have to be while the pencil were sideways because the change in weight distribution the eraser has to deal with when leaned over. It would be most stable when upright (any of this clicking if you think of the pencil as the motorcycle and the eraser as tires? I didn't get it while I was playing with the pencil for about 15 minutes).

If the weight added to the writing side of the pencil were lowered, I'd have more eraser grip while flinging it and the pencil would be more stabilized. I'm telling you, all this works. I had a separate eraser I pushed into the pencil and was changing its position.

Now, although I can't take steering into account with a pencil, you'd have to think it would destabilize the pencil an unnoticeable or slightly noticeable amount while being flung one side to the other if a steering input were involved. Where you'll notice the eraser slide is when the pencil is at or just past upright. Imagine the weight that was added onto the pencil while you're flicking it. It needs a certain amount of pressure to get the eraser to slide. More than if you didn't have that weight on it.

If you could do it, what do you think the eraser would do if you could remove that weight any time you want, and chose to do it just at the point when the eraser is at its traction limit WITH the weight. It will unweigh itself. Throw in the destabilizing force of a turning motion and an input that wouldn't make the pencil shutter at that certain weight (stabilizing force) become suddenly lighter. Any small shutter WITH the weight will be exaggerated by the sudden loss of weight. You've got Tony Elias on a pencil that is unweighted just at the right time to jiggle about, then replant itself as the weight is added back, decreasing the shuttering to a manageable level.

The things I've taken into account that make it less likely that we do this on a normal occasion is:

1. A vast majority of us don't maintain the limits of traction that the GP riders do. Very small mistakes can cause this and worse to happen when riding at their level.

2. Our bikes are heavier than the GP bikes (the current 212V is 331 lbs) so we have the added weight to keep the bike on the ground longer and lessen this effect. Downward force (weight) on the tires increases traction in this instance.

3. We hopefully do the hip-flick in quick turning situations, which requires us to move our hips one way while the bike is still in the turn the other way. That means our weight is already on the seat when we're turning to the other side. AT THE VERY LEAST our weight should be hitting back into the seat at the moment we are at the top of our flick. Tisk tisk Tony.

4. It's a demonstration of keeping our butts on the seat going from one side to the other in a SLIDING, not lifting, motion.

The error that could easily be explained away with too much power isn't so easy anymore. It was rider error.

* Also in there is the lesson that you need to get down on the bike while cornering. Lay on the tank.

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Great post Jason. This is something I dealt with last week at VIR doing levels 3 and 4. Thanks in no small part to some of the explanations on this forum, I have been able to get a firm grasp on weighting the outside peg and consequently I had good body position early on in the camp however in the switchbacks I was suffering from quite a bit of head shake. This was explained soon enough by Keith when he went into the knee to knee and the hip flick and the unwanted rider inputs you have brought up. I have to admit he made the hip flick look easier than I was able to. I had varying degrees of success throughout both days but I found out that it takes muscles and requires flexibility that I am going to have to work on.

 

So if any of you have gym exercises that will help build up the muscles used in the hip flick please let me know!

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  • 4 weeks later...

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