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The crime of adding throttle while increasing lean.

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Accelerating creates a load on the rear tire, as you know. Cornering creates a lateral load on the rear tire, and as the bike is leaned over farther the suspension is much less efficient at keeping the tire in contact with the pavement. That is the primary thing that changes when you lean it over more, your suspension is not able to handle pavement inconsistencies as well and that reduces available traction.

If a rider increases acceleration, or increases lean angle, one a time (and not TOO abruptly), assuming tires are warmed up and tractions conditions are generally good, there is some warning when the rider begins the reach the limits of traction. The rear tire begins to slide or squirm, letting the rider know that he/she is nearing the limit. However, when BOTH loads are increased at the same time, it is very easy to blow right past those warnings (AND overwhelm the electronic traction controls on the bike, if you a riding a bike with that technology) and generate a rear tire slide, which can lead to highside which is a nasty way to crash. As you go increasingly faster around corners, the lateral forces are greater and the lean angle is steeper, so there is less available traction for acceleration - thus throttle control must be more precise, and increasing the lean angle even MORE while also applying addition throttle can more easily exceed the traction limit - which could be why you got a sterner talking to on the second day. :)

It is a very common way to crash, especially on higher horsepower bikes that can deliver loads of power to the rear tire.

Riders get away with it all the time, sure. Just go to an open track day and watch, lots of riders that are trying to go fast do things like turn in a bit early, end up a bit wide on the exit, and solve that by leaning the bike over more while still rolling on the gas. Modern tires are great and they can take a lot - until they don't, and the rider suddenly has a gnarly crash and can't understand what happened.

Does that help clarify?

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19 minutes ago, Hotfoot said:

"That is the primary thing that changes when you lean it over more, your suspension is not able to handle pavement inconsistencies as well and that reduces available traction."

Brilliant.  That is exactly the key I was looking for.  Suspension working at its geometrically least efficient position. increasing throttle as a suspension input.  That totally clarifies if for me.

Thank you.

 

 

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Hotfoot,  the way i understood it is that increasing rear wheel speed at the same time decrease contact patch (aka Grip) is a recipe for disaster.  is this your take on it as well??

(Signorelli was my coach you can blame him lol) JK 

so this is why you do not want to increase at the same time you decrease My Coach actually talked to me for about 2 hrs on the phone working this out after a really big off in T11 at HPR in 2015.  this is why a stand by CSB.

 

At Roberts,  the way i remedied this bad habit on the track (racing with the MRA in Colorado) was i added to my corner routine "break in, throttle out".....and stand it up with throttle as a common routine this is somewhat subjective and again i will refer to Hotfoot, is this your experience as well?  this is what worked for me it got me cornering better cleaner smoother and chasing a championship.

;) good luck

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1 hour ago, Hellrazor318 said:

Hotfoot,  the way i understood it is that increasing rear wheel speed at the same time decrease contact patch (aka Grip) is a recipe for disaster.  is this your take on it as well??

Depending on your tires and tire pressure, leaning over more does not necessarily decrease the size of the contact patch. However, as you lean over more the suspension is less efficient at keeping the tire in contact with the pavement. 

Decreased suspension efficiency combined with the acceleration forces when you roll on the gas hard can exceed the limits of traction at the rear wheel. 

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As usual, the answers from Hotfoot are excellent.  I would like to learn from you the reason, expected benefit or reasoning behind that 40-year old habit for street riding.  According to the book, once you steer for the turn, lean the bike and crack the throttle open, nothing should change until it is time to pick up the bike, accelerate and exit that curve.

"Rule Number One:
Once the throttle is cracked on, it is rolled on evenly, smoothly, and constantly throughout the remainder of the turn.
At the point where the correct transfer of weight is achieved by the rider (10 to 20 percent rearward) by using the throttle, any big changes in that weight distribution reduce available traction.
Once the bike is fully leaned into a turn, changes in tire load, either evenly (both wheels, most easily done in a crested road situation) or alternately (front to back, back to front, from throttle on/throttle off) must then either underweight or overweight the ideal load for that particular tire/bike combination." - Keith Code

Discussing Physics a little further, let's see what happens (regarding forces) on the contact patch of the rear tire when extreme leaning and acceleration happen simultaneously.  This article shows some schematics that help us understand how the lateral (cornering) and longitudinal (acceleration) forces are acting on the rear contact patch at 90 degrees from each other.  That creates a unique resulting force that can easily grow beyond the limits of available traction (imaginary circle):

https://lifeatlean.com/the-traction-zone/

Using your example of 30-degree lean and proper roll-on throttle, here is what that rear contact patch and suspension are "feeling" (regarding simultaneous forces acting in different directions): 

Vertical force: 60% to 70% of the total weight (bike, fluids and rider).  Let's assume 600 pounds of total weight as a reference. Then the patch has 360 to 420 pounds pressing vertically down (let's use the average of 390 pounds to simplify analysis). The magnitude of that force varies as the tire rolls over crests (force increases) and valleys (force decreases) of the track or road, hence the importance of an efficient suspension that keeps the patch pressed down.  If your rear tire is able of 1 G of traction, the available friction, grip or traction between rubber and pavement is 390 pounds (it equals vertical force for coefficient of friction=1) in any direction parallel to the track or road surface.  We could draw an imaginary circle around the patch showing that limit of 390 pounds of available traction.  If the rider forces the patch beyond that limit, the tire will slide over or skid.

Lateral force for 30-degree lean angle is tan 30 x vertical force = 225 pounds pulling the tire sideways (trying to make it slide out of the curve).  

Rear suspension (which is working at 30 degrees from vertical) is "feeling" or supporting a total force of vertical force / cos 30 = 450 pounds (15% overloaded respect to the vertical position, while forces/shocks from irregularities of the track keep coming from a vertical direction).

Rearward force is 0.1 to 0.2 G (proper roll-on acceleration rate according to the book) = 60 to 120 pounds.

For those conditions, you could get away with accelerating more than recommended.  For that lateral force of 225 pounds, you could apply up to 320 pounds of accelerating rearward force onto the rear contact patch before reaching the limit of the imaginary circle of traction.  That means an acceleration of 0.53 G, which is very easy to achieve for a 1000 cc machine without much twist of the throttle (consider that a wheelie would happen for around 1 G or 600 pounds of rearward force).

Now, as you corner harder enough to increase that lateral force (closer to 390 pounds) and lean angle (closer to 45 degrees), the amount of achievable acceleration decreases dramatically.  It takes a very fine throttle control to keep the acceleration within that reduced range. Simultaneous excessive acceleration and extreme lean angle (high lateral force acting on the contact patch) can take the tire beyond its limits of traction way too easy.  And that is for properly inflated warm tires on dry asphalt, just consider the outcome for wet asphalt, dust, sand or fluids, improper pressure, poor throttle control, etc.

I find this article from Keith about G forces at extreme leaning very interesting:

https://www.motorcyclistonline.com/leaning-bike-code-break/

 

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22 hours ago, Hellrazor318 said:

At Roberts,  the way i remedied this bad habit on the track (racing with the MRA in Colorado) was i added to my corner routine "break in, throttle out".....and stand it up with throttle as a common routine this is somewhat subjective and again i will refer to Hotfoot, is this your experience as well?  this is what worked for me it got me cornering better cleaner smoother and chasing a championship.

;) good luck

Your idea is exactly right for me too.  I have to create a new routine to try to be aware of and solve my bad habits.  It's not easy.

I was/am a rookie at this, so my experience is 100% learning new things, but I am not new to racing, or pushing the limits of powered vehicles.  Two things of significance come to mind:

The act of cornering causes tires to 'crab'. for the length of the contact patch, the lateral forces are bending the tire away from 'straight ahead neutral'.  The more the force, the more the bend, until you lose grip and the tire slides.  With carts and cars you can feel where this happens and with judicious use of throttle and steering you can use this to your advantage to really increase corner speeds.  I have to assume that for the talented riders this is true on motorcycles, but because steering is caused by counter-steer which increases the crabbing effect, that adding lean acts as a multiplier, not an additive forces, and as Hotfoot said, you pass the point of slipping too fast to manage the recovery.  It must be a fine line.

Also, as I understand it you only change the shape of the contact patch by adding lean.  To change the size of the patch you need to change the weight...which takes me back to Hotfoot reminding me that throttle is a suspension input.  It has a directed and immediate effect on weight distribution.

In off-road racing sliding both tires is what you do all day long, but you are also tossing the center of gravity around with body english, something that seems much more tricky (to me) on pavement.

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We have seen riders adding throttle and lean angle at the same time and it gets to the point it leaves a horrible dark line (getting progressively worse/darker) while the 2 are being added.  Then, when the rider stops increasing lean, the dark line turns to a a nice grey line.  

I think the dark line is the front tire being stressed heavily, a number of the throttle and lean issues have the rider losing the front end, with no warning.  

There was some great slo-mo footage of Stoner adding a little lean angle, dark line coming off the tires, then he stopped and so did the dark line.

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