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Rolling On The Gas


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From what I've read in books, one of several reasons we roll on the power (aside from suspension considerations) is to help the tires increase rpm as they roll onto a smaller radius.

 

If this is so, it would seem that one would begin rolling on the power DURING the tipping/leaning action rather than waiting until the action is completed and the turning has been established.

 

Can someone explain whether or not this line of reasoning is correct? Forgive my ignorance. Motorcycle theory is new to me and I find it incredibly amazing. Gotta figure out how to save away the bucks for the two-day camp.

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The purpose in rolling on the gas "in" a corner is to stabilize the bike by transfering load weight to the rear tire.

 

The question of "WHEN" is one I thought I knew the answer to until I took level III this year.

 

Previously, I would initiate my turn and immediately dial on the gas. This has worked to measured success for me for the past few years. However, watching myself on video and having been followed by CSS instructors, I was getting on the gas BEFORE the bike was complete on its turn path. What happened when I did this was that I would push the bike wide at every turn. I just naturally compensated for it.

 

Dylan Code saw this and we discussed the negative impact to it. From that point forward, the method then turned into... Push bar to initiate turn. Get bike FULLY onto turn arc. Get back on the gas.

 

My turns were instantly cleaner and tighter, not to mention quicker...

 

Bottom line, wait until the turn is completely initiated and you are on the line before getting on the gas. If you don't, you will end up having to continually feed steering inputs to the bike to get it turned correctly. And you'll still end up going wide.

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A non-technical answer would be: brake till your apex,and accelerate all the way after apex. Now I do not mean to say that that is easy to do, but that is the right thing to do if you can.

 

To give a technical answer: The basic(and a little simplified) logic of cornering is:

m*g*x = m*square(v)*d/r

 

where m=mass, g= gravity, v=velocity, r=radius of turn at that istant, d= height of centre of mass and x= distance of centre of mass from rear contact point(hence roughly factoring in ur lean angle)

 

where mgx is the force that makes u fall into corner and m*square(v)*d/r is the force that makes u fall out, or say, run wide.

Now if u were accelerating, hence implying higher 'v', then to keep balance, you will have to do one of following:

1.lower d(means lean more)

2.higher r(means u would end up widening ur turn)

3. higher x(again meaning lean more, roughly)

 

now u cant lean beyond a certain point, becuase factors like traction, track surface, steering control, physical limit and all come in(which are not figured in above equation).

now the last point question that would arise is that this logic applies equally to getting into corner and getting out of corner..then why can u accelerate out of corner but not into it?

answer is simple: when u r coming into corner, ur 'r' is decreasing by default(means u HAVE to decrease 'v', other factors remaining constant), and when u r getting out of corner, ur 'r' is increasing by default (means u HAVE a chance to increase 'v', other factors remaining constantIt also postulates that if its a contant radius turn, you dont need to step off throttle!

 

 

now this was just a gist of cornering and i would suggest further reading if you want to get theory right.. but its pretty simple once u get the hang of it!good luck

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In one breath I laugh at the mathmatical model but in the next I understand it fully from the perspective both as a pilot and snowboard coach.

 

I have found what JeF4y said to be exactly true, lay it over, then stabilize.

 

That brings me to a somewhat generalized question. What research has been done to measure the lateral coefficient of friction at various lean angles, assuming some standard has been set for the quality of asphalt, level surface, tire material and pressure, temperature, combined mass of bike/rider. Is there a "range" beyond which lateral coefficient is exceeded due to lean angle? From the many pictures I have examined it would appear that under even the most ideal conditions, riders do not exceed approximately 65 degrees of tilt between their point of contact on the pavement and the composite bike/rider CM without having the bike going out from under them. Has this "breakaway point" been researched? I would love to see the data if it has.

 

If you apply the math you see that your apparent weight is exactly doubled at exactly 60 degrees. For example a combined theoretical weight of 500 pounds straight down at vertical would become 1000 pounds when tilted to 60 degrees (most of that force being directed laterally ACROSS the pavement and less than half of it straight down into the earth). What is interesting is that the numbers follow an alogrithmic increase. It take you 60 degrees to double the apparent force, only 10 more degrees to hit the tripling point (at approximately 70 degrees) and only 5 more to hit the quadrupling point (75 degrees).

 

In case anyone is wondering "what the heck???", my reasons for understanding this go a little beyond my own personal riding education. I will simply say that in many sports that involve similar tipping for turning, this 65 degree limit seems to hold true. I think I know why. I am curious what others may think about this. :blink:

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Trying to analyze the physics of riding is interesting. The problem is it is often difficult to apply physics to the track while riding.

 

 

The simple answer to the question posted above...

 

You don't want to be in the gas when you turn the bike because being in the gas makes the bike more stable and harder to turn.

 

When you turn you are intentionally de-stabilizing the bike to lean it over. Once this part of the turn is done you get back on the gas ASAP to stabilize the bike on the line you have chosen.

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A non-technical answer would be: brake till your apex,and accelerate all the way after apex. Now I do not mean to say that that is easy to do, but that is the right thing to do if you can.

 

Ah, I think you might find a few people (myself included) that would strongly disagree with that statement.

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Brakes to appex and gas afterwards?

 

Great in the perfect 90 degree corner after a long straight and before a short one, but otherwise not true. This doesn't reflect setting an arc before getting on the gas. If a corner was over 400m long, then you would brake before the corner to get the speed nearly there, brake for 200m into the corner then 200m out again?

 

What about an early apex to get better drive out of a corner?

 

What about a chicane where you are braking all the way through the first corner or possibly accellerating all the way through the second?

 

I understand what you were saying in terms of keeping it very simple, someone once told me this and I spent a year getting corners wrong. I build on this as the keystone for all cornering, but it is quite simply wrong! Sorry!

 

Each and every corner is different and required different reactions. As mentioned above, brake where you need to but try to be on the gas once you have your cornering arc set, unless there is another sharper corner coming immediatly.

 

Even on the road this is a bit dodgy, as you will want to have most of your braking out of the way before you finish tipping in, otherwise that road kill you hit will definatly drop you and the bike!

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Something else occurred to me today, on a long 270 degree turn (Yes we have these on West Virginia highways..especially near rivers and in the mountains). The turn radius in question was consistant throughout the 270 degree arc.

 

I realized that ROLLING ON THE GAS and STEADILY INCREASING THE GAS are two different things. Or at least so it would seem.

 

I decellerated to my "tip in reference point" (did it with the throttle and downshifting in this case), I tipped er in, then I simply brough the power on then MAINTAINED THE SAME GAS (rpm) until I was ready to exit then I INCREASED GAS to bring myself out of the turn. Worked great.

 

Had I instead INCREASED GAS from the moment my arc was established I would have eventually exceeded the limits of lateral cohesion and slid right out of the turn (or so it would seem).

 

Is this right?

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It makes sense to me. We roll on the throttle to maintain speed and to conter the effects of decreasing tyre radius as we lean it in, so as to not lose more speed than we intended to.

 

A quick sum-up: As you lean the bike over, it rides nearer to the tyre wall, where the radius of the tyre is smaller, therefore the wheel has to turn faster for the given speed, hence the rev's will go up, but due to us holidng a steady throttle, this allows the revs to drop back to where they were before the corner. This allows the bike to slow down even though we have the same throttle and same RPM. The wheel is tuning as fast as before, but on a smaller radius, hence the wheel covers less distance per revolution. Thus why we initially increase the throttle as we tip in.

 

Now imagine an endless corner, say a road island: If we drop into this island in second gear and keep increasing the throttle the whole time, we'd reach top power in the gear being used and have to change up, this will happen again and again until you are at top rev's in sixth. Now, do you think you would be travelling at the same speed you entered or a dam site quicker at top revs in sixth?

 

I believe the idea of constantly rolling the throttle on in a corner is ideal, to keep most of the weight transfered to the rear of the bike and to increase ground clearance and especially to get a good, stong, smooth drive out of a corner. But for long bends, once the roll on has commenced and we are at the desired speed and lean angle for that corner, the throttle must be maintained at the same RPM until you are at the point where you can build speed without compromising your line.

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But for long bends, once the roll on has commenced and we are at the desired speed and lean angle for that corner, the throttle must be maintained at the same RPM until you are at the point where you can build speed without compromising your line.

 

Well said, and don't forget RPM's will drop as lean angle increases.....

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But for long bends, once the roll on has commenced and we are at the desired speed and lean angle for that corner, the throttle must be maintained at the same RPM until you are at the point where you can build speed without compromising your line.

In a really long corner you might hit the limit of traction and have to stop rolling on, yes. However, it would have to be REALLY long and those types of corners are pretty rare, unless you ride freway on ramps and round abouts :)

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  • 2 weeks later...
Well said, and don't forget RPM's will drop as lean angle increases.....

I think he meant decreases?!

 

Basically, add ever so slightly more throttle than you need until you are upright, as the bike will be effectively loosing RPM from tyre radius getting larger at the same time you are trying to build RPM with the throttle.

 

On the track, you shouldn't really be thinking about this, just give the bike enough gas to almost break the rear tyre grip, or actually break it if that's the way you steer a bike.

 

On the street, just keep it smooth and build the power gradually.

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Ah, I think you might find a few people (myself included) that would strongly disagree with that statement.

Ok, lets take out braking. but you would still decelerate till the apex..or just stay on steady RPMs..right? But deceleration, in a way, is also braking!!! Constant RPMs too are deceleration(one of the posts below talks about lesser tyre circumference, hence lesser distance covered, hence lesser speed, implying deceleration). so anyway, u r braking till apex!

 

now to answer Andy, yes u r right, this was a generic, simplified and theoretical statement. in practice, each turn has to be tackled differently. but if u will analyze, then the principle would still remain same. even if it were an early apex, u still would accelerate only after reacing apex. (hint: if u r able to accelerate before reaching apex, that means u could have brought more speed into that corner)

 

now, another contoversial statement, about apexes..and lines. Ideally, there is only one perfect line. This is the line that gives u the widest arc(therefore highest 'r' and therefore chance to have more 'v'(in reference to my equation on top) and therefore higher speed).

 

but bottomline, this is all IDEAL stuff. In real world, depending upon our skills and everything, we have to find the most suitable strategies. I would not mind accepting that I cant even do 20% of all that I am talking about. BUt I am trying.

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kalkat, my friend,

 

your equation...or should i say theory...fails to take into account several factors...mathematically speaking...like the rotating mass of the crankshaft ergo forces of engine braking or lack thereof, weight transfer, friction with the road, the bike's suspension, gyroscopic forces, and most importantly...rider input. it asks me to accept several assumptions as 'given' which simply aren't so.

 

for instance, your premise of m*g*x being the 'force' that "makes a bike fall into a corner". well, the fact is...bikes don't fall into a corner. simply put, left to their own devices, excluding long term entropy of the system (like the bike losing all its v) bikes will go in a straight line unless acted upon by another force, such as...the rider. (due to the gyroscopic force of the rotating mass of the wheels and tires)

 

a certain amount of force applied to the handle bar is required to push the bike over at speed. no doubt gravity helps. but i can overcome gravity with the application of enuf reverse angular moment applied to the handlebar to push the bike back up.

 

and then the steering geometry changes as the forks compress under braking, and the contact patch of the front tire gets bigger...and then...and then...and then...

 

excluding these factors in an effort to "simplify" is like trying to simplify rocket science by excluding heat. it ain't real.

 

the simple fact is the entire system is dynamic in many ways...nothing short of calculus will work with enuf accuracy to describe it mathematically in anything approaching a realistic fashion...and any physicist will tell you...you don't really need the numbers to understand the theory.

 

but you will need to actually ride a motorcycle to prove anything.

 

naming isn't knowing.

 

hey, it's 3 am, i've been up since 8am yesterday. i'm way too tired to do math. go do the experiment with a stop watch and tell me how it works out.

 

guten nacht

 

ps in the nicest of ways...welcome to the family. it's anything but simple for us mere mortals. try reading twist of the wrist. the man's kinda been researching the stuff and proving it for, well, a lifetime. then prove it to yourself. or disprove. i don't ask you to accept anything at face value. lord knows i don't. ;)

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gracias for the comments senor.. but it aint my theory... I will try to find the link to it...but I agree..and I did mention... that it does not take into account MANY factors...so u r right about that.

 

As u might have seen on other posts..Keith himself says that u can do 2 things on a bike 1.change direction 2. change speed (though he was trying to keep it simple).. Now if u would diagnose these ACTIONS... and see the FACTORS which lead to these changes, u would c that m, g,x, v, d, r ALONG WITH MANY other factors like suspension, road condition, traction , tyre, temp, etc etc arewat enables u to change those things EFFICIENTLY.

now, to get my point across, let me classify these FACTORS:

 

1.PASSIVE: (factors which u have ABSOLUTELY no control over)road surface and conditions, weather and temp that day, layout of track,rotating mass of the crankshaft and forces of engine braking or lack thereof(unless u r gonna put a diff crankshaft or piston etc into the engine, in which case it will move to SEMI-ACTIVE category) etc etc

2. SEMI-ACTIVE: (factors which u have some control over, but not at that GIVEN point of time, while u r racing):type of tires, suspension, bike aerodynamics, ... etc etc

3. ACTIVE: (factors u have ABSOLUTE control over, at any moment, even when u r racing):x, v, d, r, body posture, positioning etc etc....

 

(now that equation was not devloped by me..I just read it somewhere...but this classification is mine...so take it with a pinch of salt ;) .. though I personally think it makes intuitve sense. )

 

Now, as you would have realized, that equation talked only about third category of factors... so yes, u r right, that i dint talk about first two categories, but as the classification tells u, the factors I took up are not the ONLY factors that r imp, but yes, they r the ONLY factors u have a chance of playing around with once u r out on the track, playing the sport!!!

 

In the end, thanks for the welcome.. I m just a learner..and thats what I am on this forum for..I fully appreciate and try my best to understand the critiques by anybody out there...though ..with a pinch of salt sometimes... :rolleyes: ..and let me add..its great to be here.. with so many people with so much knowledge.. I am gonna learn a lil bit from everybody and then go beat the ###### out of the best that exist out there!

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Ah, my mistake, dude. You go get 'em.

 

Via con dios. B)

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PS: I've modified my original post a bit in an effort to clarify some of my late night stream of semi-consciousness.

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Bloody Hell! Major Head Job!

 

Do I now have to take a scientific calculator out with me on the track, bolted to the handle bars and work out all of the above?

 

You guys have been thinking about this just a little too much. There is theory and there is explaination, then there is the N'th degree, a Masters Degree no less! I'm not really sure why the maths of it all has ended up in here? I know it doesn't assist my riding in any way knowing that m*g*x=Big Balls of Steel! I'll just get out there using the techniques Keith has provided in his books and figure out my style of racing. (Plus get on some of the courses! ;) )

 

I wonder if you lot are spending too much time on line and not enough time in the garage maintaining and looking after your bikes? :o

 

'm not having a dig at anyone, I just thought this was massively over the top for riding advice. Too heavy for me, that's for sure! ;)

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Indeed. Musta been some unresolved personal issue giving me an attitude and putting me in front of the computer at 3am "thinking" about it all and latching onto another math geek like me. Or maybe it's the snow on the driveway. Hmmm...time to go skiing. YAHOO!!

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BTW - I believe there are California Superbike Schools in the UK.

 

Hey Kalkat,

 

Thanks for the invite to Texas, mate. I'm in Pennsylvania for the "holidays" with the family. Come January I'm probably gonna bugger off to New Zealand to go race sailboats or something. In the meantime, get "A Twist of the Wrist" book and get on a track where it's safe. I recommend Keith Code's schools as the best place to start. His team is professionally trained to teach you with decades of experience doing just that. The best of the best as it were.

 

Me, Im still learnin them thar people/teacher skills things. Duh...

 

Keep up with the math. It'll take you anywhere you want to go.

 

Cheers

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