The crime of adding throttle while increasing lean.

[Roberts]

[Hotfoot]

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?

[Roberts]

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.

 

 

[Hotfoot]

Awesome, glad that helped. 

[Hellrazor318]

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

[Hotfoot]

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. 

[Lnewqban]

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/

 

[Roberts]

 

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.

[Cobie Fair]

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.

[Jaybird180]

On 8/16/2019 at 6:00 PM, Cobie Fair said:

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.

I might know a guy who knows a guy who has experienced this (sarcasm).

[tzrider]

Another factor I haven't seen mentioned is that as you lean over, the final drive ratio changes.  the difference between upright and fully leaned is the equivalent of half a downshift.  This puts the engine in a different part of the powerband and can alter the effect a given amount of roll-on has, seeming to amplify the torque as the lean angle increases.

[Hotfoot]

23 hours ago, tzrider said:

Another factor I haven't seen mentioned is that as you lean over, the final drive ratio changes.  the difference between upright and fully leaned is the equivalent of half a downshift.  This puts the engine in a different part of the powerband and can alter the effect a given amount of roll-on has, seeming to amplify the torque as the lean angle increases.

Good point, and I made great use of that while racing this weekend. My bike was geared a little too high for a particular corners so my drive out of the corner was suffering, so I tried changing my line to stay leaned over a bit longer - somewhat counter intuitive for getting a good drive, but it worked. Before, I was riding a more squared off line and standing the bike up but then  my RPM was too low; leaving it leaned over a bit longer put me about 500 rpm higher and the bike did not lug on the exit. (To be clear, I wasn't ADDING lean angle - I was just maintaining my lean angle longer instead of doing an earlier pick-up.) On my low horsepower bike it made a difference, and I was very happy I knew how to apply that information!

[SRod321]

So I THINK I was guilty of doing this this past Monday at NJMP on thunderbolt. It was lap two of session six on the day, turn 7 (left hander, second turn after ther hill). The strange thing and what confused me at first was that before that session, all morning and afternoon I was, in my humble opinion crushing that corner. I was getting good drive out of it all day, using what i believe was a good line(I was trying to follow the line JJ used when he recorded me this past July in level 3) and decent BP. The track was great, sunny, clear, temp of 69°F, tire pressures were at 28 psi. In session six, second lap, I proceeded to do what I believe I was doing all day, as soon as I was done steering, I saw my exit line and cone and began to roll on the throttle. Suddenly I felt the rear start to come around to which i responded with a semi flabbergasted and laughing "aww fudge" only, as in the movie A Christmas story,  "i didn't say fudge". Bike low sided as I let go and sat down a little hard and slid a few feet. I was able to get the bike back up and ride it back to the pit believing that I added lean and throttle causing this low side. I was talking about it with a guy from the intermediate group (i was riding novice) who was next to my trailer and he made a comment about my tires saying that he believed it wasn't my technique or anything i did but my tires that failed me. I didn't wanna believe that at first because I thought it was totally me until I looked at the wear on my tires. He stated that riding on the tires I had was like riding on cinder blocks. I recalled that a month prior on these same tires, the rear slipped a little bit coming out of the last turn at NYST twice in two different sessions and I KNOW for a fact that I wasn't leaning the bike enough to ride past the edge and slip, my wear marks indicated and still indicates that i had some room for error. So... now I'm wondering if in fact it was the tires or me. It's messing with me mentally and this was my last track day of the season so I know this is going to be on my mind all off season until I go back there smh. The tires are metzeler m5 interacts which are supposed to be (although it's a street tire) a decent tire and they have plenty of life on them. I added a picture so you can see that I wasn't even on the edge of the tires grip. I guess I'm searching for an answer or guidance on whether it was my technique or if it's time for better tires/tire warmers. Sorry for the novel and thanks in advance for the input/insight/feedback.

[Jaybird180]

Considering there are very few left handers and that it was the 2nd lap then I understand how it could lead someone to consider that the tires weren’t yet warm.

Something to consider: What did the bike do on the previous lap? What was your comparative pace? Did it slide or give any warnings on that first lap going left? How was the right side?

When you pit from your previous sessions, are the tires hot to the touch? If not, I wouldn’t open your wallet on the tire warmers just yet. I’ve never run Metzlers but Dave Moss told me that he doesn’t let riders run less than 30psi until their pace is at a certain point that warrants it. I didn’t inquire further on his rationale.

[SRod321]

Thanks for the reply jaybird, going over the video footage from that day I was averaging about 2 mins a lap(not very fast, I know), but it felt consistent every lap. Left and right turns felt the same. I never felt any slip or give on the first lap of any session because I dialed it back for the first lap each time out. After the first lap, I felt like the bike gripped a little better so I would up my pace. This was the case in that session where I went down. It gave without warning. I didn't notice anything different between the lefts and few rights. I never thought to check tire temps after each session so I can't give you any honest feedback on that. I've been running 28 psi because it's what one of my coaches at NYST always had me set my pressures to. I would imagine (forgive me if I'm mistaken on this) that lower tire pressure to a point would give you a little more grip because of a bigger contact patch? I gotta take another good look at the rear tire and inspect it. 

[Jaybird180]

Yes, it's true that you get more tire in contact with the pavement with lower pressures (to a point), but despite the myths contact patch size isn't the primary factor in providing tire grip. Tire grip restated in physics terms is the coefficient of friction between the two surfaces (road and rubber) and the myth is that bigger contact patch = more grip.

The tires act as part of the suspension system, responding to the irregularities in the pavement often in ways the forks and shocks cannot. This would be referred to as compliance of the tire. When the tire is not in physical contact with the pavement, you have no grip. As a tire (internally) heats up, the air inside increases pressure, pushing from the inside on the tire and giving it more of an inflated shape and hardness - pressure. Tire pressures are set in such a way to allow for running conditions to put the tire into the optimum temperature range for the tire to adhere to the pavement based on it's chemical makeup (the rubber and the other "stuff" the manufacturer puts into the tire) and to inflate the tire to a workable compliance based on expectations of performance working in concert with the forks and shock to give the rider what is needed - friction (and absorbing some bumps is nice too). All of this is the long way of saying: don't take tire pressures as gospel, they can be bike, rider, asphalt composition, surface and ambient temperature specific. Some tire brands are more tolerant than others of what the proper range would be. Dave Moss has talked about some Michelin tires being 1/2lb sensitive!

I am very interested in knowing if when you felt the bike "gripped a little better" if you ramped it up a little bit or aggressively? What was your mental state knowing this was your last session of the season? How was your throttle control and what was your sense of connection to the rear wheel as it came around? Did the RPM rise?

I'm very curious as to why you lost the rear and not the front as @Cobie Fair described above. I'm also curious as to how this didn't turn into a highside.

[SRod321]

I gotta be honest, given how the previous sessions went, i figured one lap was good for a warmup seeing as how that's what I did from the second session on (in the first session i gave it two laps). So after one lap, i felt better grip and got a little more aggressive. I had one more session left so I didn't expect this one to be my last. Wasn't "going in" as if it was the last run of the season. Throttle control felt smooth, I remembered to ROLL it on, I didn't whack it open. I don't recall the RPMs shooting up, I just remember the rear coming around. I was pretty surprised that it wasn't a high side too. The bike didn't tumble either. It just laid down and slid on to the dirt. The frame slider, rider foot peg, passenger foot peg and rear spool saved the engine case. One thing i do remember was very briefly when i began to roll the throttle, i didn't feel the settling/squatting of the rear I had felt previously throughout the day when driving out through the exit (i guess this is the connection with the rear that you're talking about?) but before I could put it together the rear was sliding out. I have video footage of my tach because I had a go pro sitting on the gas tank cover so I gotta go review that and see what I made the engine do and whether or not I really rolled the throttle or whacked it open. 

[Hotfoot]

How many miles or track days do you have on that tire? 

[SRod321]

15 minutes ago, Hotfoot said:

How many miles or track days do you have on that tire? 

This was my third track day on this motorcycle with those tires, however, those tires do have some mileage on them. The actual amount I honestly don't know (I know, shame on me, I know better), i should've changed them but due to my work schedule I couldn't make the time to get new tires, I figured I could squeeze one more track day out of them, after all, I'm not at the level where I burn through tires easily. They do have a lot of meat left on them though. 

[SRod321]

Here's a short clip of the low side. I'm still wondering if it was the rear tire or the front that gave out. @Jaybird180 I also noticed that the RPMs do rise up a little quickly but I think that was after the rear tire gave out and started to come around. I don't remember ripping the throttle open, just cracking and rolling it, but, I am starting to wonder if the roll one was a little too fast??

I hope the video upload comes out decent.

[Jaybird180]

When you ride, do you get arm pump? Cramped hands?

[SRod321]

10 hours ago, Jaybird180 said:

When you ride, do you get arm pump? Cramped hands?

No, very rarely if at all and I'm cognizant of it. I remind myself to grip the tank and relax if it does happen. That wasn't the case here, I was completely relaxed, no tension in the hands. The only times I ever feel my hands tense up really if it all is in the transitions in turns 3-4-5, and that's only if my position on the bike is off. Again, something I notice very quickly and correct. 

[Hotfoot]

I asked about the mileage on the tire because it looks like it has a lot of road miles, the center looks flattened. That can affect  handling, and overall age can affect grip, the rubber can get dried out and less pliable. I do think, especially after seeing your pace and leam angle on the video, that age of the tire contributed, and possibly the tire type as well- I don't know much about those tires but looks to me like you need to be on track day tires, something more like Q3s or Q4s.

When you watch the video, do you see one precise and definite  steering input, or do you see more than one change in lean angle? 

[SRod321]

@Hotfoot It could just be me but I think i see a slight second one just before i start to roll the throttle and the tire gives. Thanks for the input, I had a suspicion that the tires could have been the biggest contributing factor along with some rider error on my part but, being as fairly new to track riding as i am (3 track seasons under my belt, total of 11 track days) I was leaning more towards the latter being the root. I couldn't help but scratch my head when watching the video though and wonder if it was really all me or some tire grip factor. These tires are definitely getting tossed this off-season for some Q3s. I was gonna actually go with those before this track day but I didn't have the time to get it done. 

[Hotfoot]

I see a second steering input also. Could be that the roll on was already starting as you leaned it that extra bit, or maybe you were already near the limit (for those tires) and the extra bit of lean was enough to break it loose. I can't hear it well enough on the video to tell for sure but that extra lean combined with some throttle application could definitely have caused the rear to slide without warning.