A visual representation of available traction

[Motofool]

A visual representation of available traction

As motorcycle riders we all know very well that there is a limit placed on the amount of available traction we have during riding.

We also know that if you happen to stray past that limit then the consequences are often not so good, unless of course you have the necessary skills to deal with it.

However, while we know that the limit is there and we don’t want to exceed it, for many it will feel like some vague area that they aren’t really familiar with and don’t know at what point it exists.

To combat this lack of clarity and give riders an idea of what the traction limit looks like, there is a commonly used visual representation of the traction zone (also known as the traction circle) that demonstrates how we can best use available traction.

What is it?

As the picture to the right shows, the traction circle is shown as a simple graph, with traction being shown as the accelerative force acting against you, the bike and the tyres in every direction.

Now, for a lot of people the only known definition of acceleration will be the 0-60 time of their bike or car, but here we are talking about the measurement of acceleration felt as weight – known as g-force, or G for short.

So just like when accelerating in a straight line, you are also experiencing this accelerative force (g-force) during braking and turning too. This common relationship handily allows us to plot these accelerative forces on the same graph.

For a competent rider on a well sorted bike with good rubber, the maximum accelerative force that can be applied in any direction will be around 1G. In this case, 1G will represent the outer limit of the circle on the graph.

Using the graph

For example then, if you imagine being hard on the power in the straight line on a 1000cc bike, you would find yourself plotted on the graph near the top of the vertical line. Similarly, braking hard in a straight line would be plotted near the bottom of that same axis.

At maximum lean in a right hand turn, as you would expect, you would see yourself plotted out to the right hand edge of the circle on the horizontal line.

It’s only once you start using a combination of acceleration or braking with turning that you’ll see the point come away from either axis on the graph.

The picture above shows what the graph would look like if you were at moderate lean to the right and applying moderate acceleration at the same time.

Too Much Throttle At Lean

Looking at this representation then you can quickly see what it is that causes riders loose traction. Imagine another rider at maximum lean in a right hand turn, the graph to the right shows exactly what happens when they get too greedy with the throttle mid turn.

They step out of the traction zone because they’re asking the tyres to deal with too much accelerative force.

Equally, the same would happen on the entrance to a corner.

If you’re hard on the brakes in a straight line and you try to turn, thereby adding lateral g-force to the tyre, this will more than likely exceed that 1G limit and again, you would lose traction.

It’s clear then that your job as a rider is to make sure that you stay within this traction zone at all times by keeping the force acting against the tyres under that maximum 1G.

Even if this does seem incredibly obvious to you (don’t apply too much power at high lean etc), I think a visual representation like this gives you a good mental picture of what’s happening while out on track, and it’s good to concentrate on the total of all forces we place on our tyres, rather than breaking up acceleration, braking and turning into separate things to concentrate on.

Looking at it this way will also improve how you spend your concentration. As you exit a corner where most of your attention would have been feeling available side grip, as you pick the bike up and move yourself away from the horizontal axis of turning, your concentration will shift to feeling for grip as you apply your exit power.

If you want to get the most out of you and your bike, evaluate one of your laps and ask yourself if there are clear points where you are not near that maximum 1G limit of your traction zone. For example if your bike is upright and you’re not accelerating or braking, you’re coasting, thereby not using all available traction.

As you become a better track rider and you get faster you will be spending more time near the outer boundaries of the circle, and staying near the outer reaches of the zone will yield greater results in the way of lap times. That is essentially why top level racers are as fast as they are, because they can go near (and sometimes a little past) the limits of traction and stay there consistently.

Side note: The shape of your traction zone will never be a perfect circle because different capacity bikes will outperform others in different areas. Also it has been shown in various data acquisition tests that some bikes can accelerate harder at slight lean as opposed to sitting vertically. I would guess due to the larger contact patch that we get at modest lean angles.

[akima]

A nice simple explanation. Thanks Hernan

[greenaero]

Stay inside the circle!! Excellent post Hernan!

[Kscreations08]

Hey Hernan. I love the visual representation but it poses a question for me. Related to this comment:

Originally Posted by Motofool

Be aware that you have just reached your vulnerability peak.

Go slow, practice counter-steering, moderate braking and swerving (one at a time, never combined) in parking lots and ride super-alert.

Hope you have gone through the threads of the Riding Skills section.

My focus is the Braking and swerving part. The permit test, booklet, practice test online, and many other places have specified the one at a time, just like you. I've seen it in bold print and all caps and italics and everyway else you can imagine to add emphasis to written word.

As is proven on every ride, moderate acceleration with moderate lean will keep you well within the traction limits of the represented circle. Therefore, wouldn't moderate brake and moderate lean also be acceptable? It would just be on the lower end of the graph, right?

Fear not. I am not asking so that I can start testing limits. I have every intention of riding slow and playing keep away out on the concrete rugby field

Just trying to get a better understanding of the forces at work here.

Thanks!

[Motofool]

Originally Posted by Kscreations08

............As is proven on every ride, moderate acceleration with moderate lean will keep you well within the traction limits of the represented circle. Therefore, wouldn't moderate brake and moderate lean also be acceptable? It would just be on the lower end of the graph, right?.................

You are correct.

The difference is here:
- The front tire can handle less overall load: that circle for the front tire is smaller than the for the rear, about 40/60.
- It is too easy to apply excessive front brake too soon (a force more or less aligned with the path of the front wheel), much easier than excessive acceleration force (at least for our Ninjettes).

Please, read these:
http://www.ninjette.org/forums/showthread.php?p=730748

http://www.ninjette.org/forums/showthread.php?t=114555

[dfox]

Originally Posted by Motofool

- The front tire can handle less overall load: that circle for the front tire is smaller than the for the rear, about 40/60.

as someone who seems to have a good grasp on physics, this comment surprises me and seems to be an over-simplification to the point of being incorrect.

Static friction is static friction. Assuming the front and rear tire are made of the same types of rubber and are on the same surface, they both have equal maximum "load" when weight has been properly loaded.

The limiting factor in breaking and steering simultaneously is achieving proper weight transfer to load the front wheel. Apply too much breaking force or turning force before loading the wheel and you'll go down.

Additionally, the failure mechanism for the front wheel is dramatically different from the rear wheel, so you want to give yourself "cushion" for error. A locked front wheel quickly results in a crash while a locked rear wheel allows time for correction before you go down.

[csmith12]

Originally Posted by dfox

Assuming the front and rear tire are made of the same types of rubber and are on the same surface, they both have equal maximum "load" when weight has been properly loaded.

I am not a physics expert or anything, but the fact that the contact patch of the front is smaller.... just might have a little to do with his statement. Food for thought...

[dfox]

Originally Posted by csmith12

I am not a physics expert or anything, but the fact that the contact patch of the front is smaller.... just might have a little to do with his statement. Food for thought...

contact patch has absolutely nothing to do with available static friction.

I'm not going to get into a(nother) physics debate, but feel free to google the definition of friction to find out yourself.

[csmith12]

I can't debate physics, that's for sure... But I do know what works in the real world, and from the real world perspective, the graph is incorrect while midcorner. It assumes that the front can take as much as the rear. And that is just not so... Loading the front as much as the rear will put you on your arse. Been there, done that.

The graphic below illustrates what I feel.

[Motofool]

Originally Posted by dfox

as someone who seems to have a good grasp on physics, this comment surprises me and seems to be an over-simplification to the point of being incorrect.

Static friction is static friction. Assuming the front and rear tire are made of the same types of rubber and are on the same surface, they both have equal maximum "load" when weight has been properly loaded............

I may be wrong, but I have been so for almost two years:

http://www.ninjette.org/forums/showp...2&postcount=43

http://www.ninjette.org/forums/showp...3&postcount=46

To me, the front contact patch has been and will be the weakest link in the chain of traction and of keeping the rubber down.



I tend to agree with this quote:

"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

[Kscreations08]

You had mentioned g-forces in the OP. Could the front have less capability because of the 300 something pounds being thrown on it in braking? I recognize that the back has the same weight on acceleration but the back isn't on a swivel (front tire turns, back tire is stationary from an x-axis perspective. Do you know what I mean?

[alex.s]

i wrote a blog on why i think this is an oversimplification. if you were to use that graph as it is, the grey circle doesn't really mean anything. the size of the grey circle changes depending on a lot of things that change very quickly. if you are good, you can make the circle bigger. going outside the circle doesn't mean crashing. the faster you are going the more cushion you have with going beyond those limits it seems like. maybe just the wheels turning faster.

[akima]

I don't think the visualization that @Motofool has posted is supposed to be a perfectly accurate representation of all physical behaviour of a motorcycle and account for all known physical variables. I don't think there is even any evidence that it's attempting to do that: there's not even any numbers on the axes.

I doubt very much that MotoGP riders sit around a table tweaking this diagram's oval shape and a range of numbers on the axes to help understand and improve their track performance (ok... maybe Ben Spies does ).

If you're a new rider you'd probably find this diagram a hell of a lot more useful than advice targeted at track riders, or physics equations. It simplistically shows how combining the 2 major inputs a rider can make to a bike (turning Vs. adjusting-speed) effects grip.

I know of a bunch of people who would have benefited from seeing this diagram before they started riding. (They crashed because they applied heavy braking while turning - common mistake.)

My level of understanding of riding has progressed a long way from needing a diagram like this, but I can still appreciate the graceful design.

I guess it's a bit like blutak. It'll do a great job of holding up your cheap posters, but for heavier, more expensive things (framed paintings and TVs) you're going to need better tools. The new rider needs their blutak. The more experienced rider needs their nails (and perhaps some appreciation for the blutak that served its purpose).

[Kscreations08]

Originally Posted by akima

I guess it's a bit like blutak. It'll do a great job of holding up your cheap posters, but for heavier, more expensive things (framed paintings and TVs) you're going to need better tools. The new rider needs their blutak. The more experienced rider needs their nails (and perhaps some appreciation for the blutak that served its purpose).

*sniffle* ... That was beautiful Akima

I didn't mean to make it an arguement. I'm here to learn first and ride later

[akima]

[dfox]

Originally Posted by Motofool

I may be wrong, but I have been so for almost two years:

To me, the front contact patch has been and will be the weakest link in the chain of traction and of keeping the rubber down.

The available friction force at the front tire, maybe. The reason you have less available force is because of a lack of weight transfer. If you properly transfer weight to the front tire, it has just as much traction as the rear would with the same weight transfer. The issue is really that most people overload the front tire before properly loading it. Hence, why we all recommend that people don't just "grab a handful of break". If you do, you go down. If you ease on, you can gradually increase the breaking force as the weight transfers.

Contact patch does not change the available friction. F(friction) = coeficient of friction * Mass * acceleration (gravity). In our case F=μmg. Nowhere in that equation is surface area.

Contact patch also will not change just because you stand a bike upright in a curve. All other things equal (turn radius, rider, tire pressure, etc). a bike at a 20 degree lean will have the same contact patch at a 0 degree lean. Contact patch is directly related to the weight of the object and the pressure in the tires (pounds per square inch). To calculate your "contact patch", figure out the weight that the tire is supporting and divide that by your tire pressure. Unless you change the weight supported by the tire, your contact patch will ALWAYS be the same, regardless of lean angle.

I'm sorry for turning everyone's world upside down, but these are the facts, as presented by physics.

I highly recommend reading this page. http://www.stevemunden.com/friction.html

[csmith12]

Originally Posted by dfox

Contact patch also will not change just because you stand a bike upright in a curve. All other things equal (turn radius, rider, tire pressure, etc). a bike at a 20 degree lean will have the same contact patch at a 0 degree lean.

Negative sir, your gunna have to do more homework. Tire manufactures maximize contact patch for the given application of the tire. For example; a dunlop race tire will have the largest contact patch size at a 45 degree lean angle.

[dfox]

Originally Posted by csmith12

Negative sir, your gunna have to do more homework. Tire manufactures maximize contact patch for the given application of the tire. For example; a dunlop race tire will have the largest contact patch size at a 45 degree lean angle.

I don't design tires, nor try to. If they add structure to a tire to modify it's strength and provide additional contact patch at certain lean angles, then that's great. It still doesn't help with available friction. Read that article I linked if you refuse to listen to what I posted, because I don't have time to go into the same depth he did.

[akima]

Originally Posted by dfox

Contact patch also will not change just because you stand a bike upright in a curve. All other things equal (turn radius, rider, tire pressure, etc). a bike at a 20 degree lean will have the same contact patch at a 0 degree lean.

...

I'm sorry for turning everyone's world upside down, but these are the facts, as presented by physics.

Originally Posted by csmith12

Negative sir, your gunna have to do more homework. Tire manufactures maximize contact patch for the given application of the tire. For example; a dunlop race tire will have the largest contact patch size at a 45 degree lean angle.

Originally Posted by dfox

I don't design tires, nor try to. If they add structure to a tire to modify it's strength and provide additional contact patch at certain lean angles, then that's great.

@dfox: A simple "oops, sorry, my bad" would be appropriate. I'm sure you've got lots of useful knowledge to share, but I can't take you seriously if you can't be honest and polite when you make a mistake.

[csmith12]

Whoa there pardner.... I cannot debate about friction, I know no better. But your statement did include inaccuracies about the contact patch. Nothing more... I did read the article, it was interesting.

[dfox]

Originally Posted by akima

@dfox: A simple "oops, sorry, my bad" would be appropriate. I'm sure you've got lots of useful knowledge to share, but I can't take you seriously if you can't be honest and polite when you make a mistake.

good point. i've had a crappy day of driving on highways with massholes. my bad.


If tire manufacturers have come up with ways to change the tire structure, I can certainly see increasing contact patch. My statement regarding tire patch size being directly related to weight and psi assumed there was limited rigidity in the tire itself... discussing an inner-tube, if you will. It was a simplification that I now know is a poor one. I need to digest the info and think about it more.

[ally99]

As always, Hernan, you are an incredible teacher. Thanks for sharing your knowledge!

[ally99]

Originally Posted by Motofool

However, while we know that the limit is there and we don’t want to exceed it, for many it will feel like some vague area that they aren’t really familiar with and don’t know at what point it exists.

To combat this lack of clarity and give riders an idea of what the traction limit looks like, there is a commonly used visual representation of the traction zone (also known as the traction circle) that demonstrates how we can best use available traction.

One of the quickest ways to really learn the limits of traction is to go over them. No one wants to crash, but it happens to most riders at some point. We learn best from our mistakes if we are willing to admit first that we made one and then reflect to figure out what the mistake was and how to do better the next time the situation presents itself. Traction is compromised by inputs, and there's only so much of it before one runs out. The diagram, though simplistic, is a good descriptor for most folks' limit of riding. Those who advance their skills at the track and/or racing or make modifications to their bikes' suspension, tire choice, etc will have slightly varying circles, but for the common street rider, it is a perfect illustration.

The traction circle is also known as the traction pizza in Lee Parks' Total Control. He says, "Let's say that we have ten slices of available traction in our pizza. If you let Mr. Cornering have all ten pieces, you will have none left for Mr. Acceleration and Ms. Braking. That might be ok assuming you don't need Ms. Braking's services. Of course, if you give eight slices of pizza to Mr. Cornering and attempt to have Ms. Braking stop you in a hurry, you may run out of pizza and fall. The moral of the story is to always keep some spare pizza for any unexpected guests. In reality, things are a bit more complex than divvying up on 10-piece pizza. Each tire must share its pizza with the other tire, and the tires can steal slices from each other. However, by doing so, some of the toppings may fall off, reducing the total amount of pizza available." For each input (braking, heavy acceleration, leaning, rolling off the throttle {engine braking}), your amount of available traction lessens. You are at maximum traction when riding in a straight line with light throttle.

Originally Posted by dfox

Hence, why we all recommend that people don't just "grab a handful of brake".

Contact patch also will not change just because you stand a bike upright in a curve. All other things equal (turn radius, rider, tire pressure, etc). a bike at a 20 degree lean will have the same contact patch at a 0 degree lean. Contact patch is directly related to the weight of the object and the pressure in the tires (pounds per square inch), your contact patch will ALWAYS be the same, regardless of lean angle.

Fixed your "brake" to add a tiny bit of credibility to your post.
The contact patch changes with each degree of lean and will obviously NOT always be the same regardless of lean angle. Modern-day tires use a multi-arc profile which gives the benefits of a more narrow tire when quick flicking while also acting as a wider tire while leaned over. It actually increases the contact patch the more the bike leans, but there is a helluva lot more than simple contact patches that affect traction, and the front tire can most definitely be overloaded easier than the rear when cornering if braking forces are incorrectly added to the equation.

Edit: Ahh, yes, here it is. I knew I remembered that diagram in one of my books.

[dfox]

Originally Posted by ally99

The contact patch changes with each degree of lean and will obviously NOT always be the same regardless of lean angle. Modern-day tires use a multi-arc profile which gives the benefits of a more narrow tire when quick flicking while also acting as a wider tire while leaned over. It actually increases the contact patch the more the bike leans, but there is a helluva lot more than simple contact patches that affect traction, and the front tire can most definitely be overloaded easier than the rear when cornering if braking forces are incorrectly added to the equation.

So I've been mulling this over in my head, thinking about contact patches and what not, and I think we've gotten too far off course, and that's likely my fault. I will try to summarize this concisely.

Contact patch does not affect the available friction. If we were to take a snapshot of a rider in a turn and insert a larger contact patch without changing anything else, the available friction will be the same. The rider will not be able to take any harder of a turn, period.

Where things get confusing is when we start talking about "loading" a tire. When you progressively roll on the throttle or progressively pull the brake lever, you are transferring load to the respective tire. You now have increased friction in that tire because of the load shift. As you load this tire, the contact area increases because it's now carrying more load. The increased contact patch is an un-related side-effect of how a tire functions. The same increase in friction capacity would happen even if the tire were 100% rigid and the contact patch did not increase.

The benefit of a larger contact patch is more room for error. When you're leaning over, those asphalt snakes and gravel bits are now a bigger deal. You need a contact patch wide enough to bridge the snake without temporary loss of traction.

bottom line... the front tire has the same capacity as the rear tire given that the same load is being transferred through the tire, but less room for error when it comes to inconsistencies in the pavement.

[Motofool]

Originally Posted by ally99

As always, Hernan, you are an incredible teacher. Thanks for sharing your knowledge!

Thank you, Ally; but I must clarify that the article and schematics of the first post correspond to the link at its beginning (I always write quotations in blue).

I posted it because I agreed with it and because I believe that it is a good representation for the many new riders that we have signed-in for Ninjette.com recently.

My explanation about simultaneous braking and swerving may not be strictly accurate, but I hope it clarified Kscreations08's question.

I also believe that @dfox is correct about the complexity involved in loading a tire while a bike is leaned.
Standing in front of a leaned bike, we could see that there is only one force, but we can decompose it into a vertical force (which is the percentage of weight stood by that tire) and a horizontal force (which is proportional to the speed and sharpness of a turn).



That horizontal force twists and bends the carcase of the tires around the zone of contact with pavement (in a dynamic way; one contact patch after the other).

Here is where the traverse section of each tire makes a difference.
At least in my opinion, a bigger tire can handle those forces (of equal intensity) with less deformation; hence, keeping better suspension (cushion action against the vertical forces) than a narrower or of smaller section tire.

In addition, the front contact patch has a burden that the rear patch does not have (or just less): the slip involved in the steering.
Slip is the relative motion between the front tire and the road surface while steering (the tire points in a different direction than the actual tracking of the bike).



That means that as area X of the rolling surface approaches the zone of contact, it gets deformed sideways in order to provide the steering slip and then it recovers its normal shape as it leaves the zone of contact.

The following area Y will contact the pavement off the line toward which the front tire points.

Regarding friction; yes, a solid chunk of rubber will have a well defined resistance to slide over dry asphalt, regardless the area of contact.
That is due to a combination of attracted electrons (at molecular level) and mechanical interlock (natural to the typical roughness of both surfaces).

A tire has more factors acting on its resistance to slide over dry asphalt.
Think of a tire as a spring made of air and viscous rubber.
A softer rubber with bigger air cushion better digs deep into the crevices and gross irregularities of the road.
That mechanical lock adds to the traction that comes from the coefficient of friction alone.
More contact patch area means more crevices and irregularities into which the viscous fluid (rubber) can flow, resulting in more grab (no much, but little here and there helps).

Lastly, the slip effect induced by the steering makes any static friction not so pure.
A complex combination of static and dynamic (sliding) friction occurs in real life conditions.
As any object slides easily ones in movement, the coefficient for dynamic friction is always smaller than the static one.

Again, in my personal opinion, a leaned front tire will have proportionally more loads to deal with, ......... unless your engine has enough torque to overwhelm the rear contact patch.

The whole idea of accelerating during a turn is to release the front tire of some of those loads.
Keith Code recommends 1~2 G of acceleration, which in most bike sis enough to load the rear with around 60%~70% of the total load.

For braking on vertical position and straight line, yes, the more weight on that front patch, the more capability to "grab" the pavement and to stop the bike it has.
Maximum load and hence friction (traction) is only achieved after the contact patch is fully loaded against that asphalt.

Rolling on wet roads reduces that capability around 30%.
Here are the microscopic details of that:
http://www.ninjette.org/forums/showthread.php?t=136773

Not trying to argue or to be know-it-all-always-right here (well, ... maybe a little ).
I also had a long heavy day and just want to "di-confuse" our newbies.

Very sorry for the TLTR post.

[dfox]

Originally Posted by Motofool

In addition, the front contact patch has a burden that the rear patch does not have (or just less): the slip involved in the steering. Slip is the relative motion between the front tire and the road surface while steering (the tire points in a different direction than the actual tracking of the bike).

More contact patch area means more crevices and irregularities into which the viscous fluid (rubber) can flow, resulting in more grab (no much, but little here and there helps).

Lastly, the slip effect induced by the steering makes any static friction not so pure.A complex combination of static and dynamic (sliding) friction occurs in real life conditions.As any object slides easily ones in movement, the coefficient for dynamic friction is always smaller than the static one.

You make some good points. The round nature (both round as in a wheel, and round in cross section) of a tire basically requires that there is a combination of static and dynamic friction occurring simultaneously. This occurs at all times, not just while steering.

I think it's prudent to make it clear that while in the middle of a turn, the front wheel is not the only one experiencing forces related to steering. The large force we feel in a turn is called camber thrust, and this occurs on both front and rear wheels alike. Although with a larger cross-section radius on the rear wheel, it's likely not as strong on the rear as the front; it still exists on the rear wheel.

I will again, reiterate that contact patch does not make a difference. This can be shown by calculus and I'm surprised I can't find a website that breaks this down, it's how it was explained to me back in college so I figured I could find something. I just don't have time to do it. Basically... take your contact patch and break it down into very tiny areas. Your total friction force is now the sum of the friction force at all of the areas. To figure out the friction force at one of those tiny little areas, you use F=µmg or F=µN, where N is the normal force pushing that one tiny section of tire against the ground. In order to determine N for this tiny area, you need to divide the total force acting through the entire tire by the percentage of area you're looking at for this tiny area. Now this tiny area only has a very small normal force acting on it, and thus a small friction force. If you add more of these tiny areas (by increasing contact patch), the normal force acting at each area keeps getting smaller and smaller because you're dividing the force through the tire by the area, and you just increased your contact patch. Your overall friction force for the tire is still the same. In this way, it doesn't matter how many cracks and crevices that your tire can grip on, because the more it can grip on, the less normal force it has to create friction at each of those. It's counter intuitive, but it's physics. Start melting tires, (not just hot and sticky, but literally melting them), and then you get into a whole different range of physics where surface area will matter. I would imagine professional racers find themselves skirting this line, but for the average rider, and even likely the average racer, this likely isn't the case. (sigh... this needs to be shown graphically and I just don't have the time)

[Kscreations08]

Originally Posted by ally99

One of the quickest ways to really learn the limits of traction is to go over them...

Lmao. I know you didn't mean it this way but I read that as "Want a good lesson in physics and friction? Push it and bite it. Gravity is a great teacher"

Originally Posted by Motofool

My explanation about simultaneous braking and swerving may not be strictly accurate, but I hope it clarified Kscreations08's question.

To be honest, I think I opened a big can of complicated worms that I can't even pretend to understand. For now, as a newbie, I'll just stick with "Don't do it. It's bad." lol

[Motofool]

Originally Posted by Kscreations08

..........To be honest, I think I opened a big can of complicated worms that I can't even pretend to understand. For now, as a newbie, I'll just stick with "Don't do it. It's bad." lol

It is not complicated at all.

Represent this in your mind:

Lean angle _________________________^_______________________ Front brake

[Motofool]

I have found this video that clearly shows at low speeds how easily the weakest link of traction (the front contact patch) can be overwhelmed by excessive steering inputs.
Note how the bike is not accelerating in each event (too much weight on the front tire):

Link to original page on YouTube.

This rider, however, manages reaching the limit of traction, with bigger lean angle and a heavier bike, but using precise-smooth steering and acceleration timing:

Link to original page on YouTube.

That front contact patch is as important as small.
Being not bigger than a credit card, it only gives the best accords to the most tactful players.

[Kscreations08]

Why does this thread feel like it was so long ago =)

As always Motofool

Pushing that available traction some more:

Link to original page on YouTube.

[Motofool]

Link to original page on YouTube.

[kdogg2077]

Originally Posted by Kscreations08

Why does this thread feel like it was so long ago =)

As always Motofool

Pushing that available traction some more:

Link to original page on YouTube.

Mucho impressive.

[Worldtraveller]

Originally Posted by Motofool

Side note: The shape of your traction zone will never be a perfect circle because different capacity bikes will outperform others in different areas. Also it has been shown in various data acquisition tests that some bikes can accelerate harder at slight lean as opposed to sitting vertically. I would guess due to the larger contact patch that we get at modest lean angles.

Interestingly, and I'm gonna go see if my google skills will find one, the actual traction 'circle' winds up being more heart shaped.

here: http://www.datamc.org/2013/05/28/x-y...action-circle/

[Worldtraveller]

Originally Posted by dfox

You make some good points. The round nature (both round as in a wheel, and round in cross section) of a tire basically requires that there is a combination of static and dynamic friction occurring simultaneously. This occurs at all times, not just while steering.

I think it's prudent to make it clear that while in the middle of a turn, the front wheel is not the only one experiencing forces related to steering. The large force we feel in a turn is called camber thrust, and this occurs on both front and rear wheels alike. Although with a larger cross-section radius on the rear wheel, it's likely not as strong on the rear as the front; it still exists on the rear wheel.

I will again, reiterate that contact patch does not make a difference. This can be shown by calculus and I'm surprised I can't find a website that breaks this down, it's how it was explained to me back in college so I figured I could find something. I just don't have time to do it. Basically... take your contact patch and break it down into very tiny areas. Your total friction force is now the sum of the friction force at all of the areas. To figure out the friction force at one of those tiny little areas, you use F=µmg or F=µN, where N is the normal force pushing that one tiny section of tire against the ground. In order to determine N for this tiny area, you need to divide the total force acting through the entire tire by the percentage of area you're looking at for this tiny area. Now this tiny area only has a very small normal force acting on it, and thus a small friction force. If you add more of these tiny areas (by increasing contact patch), the normal force acting at each area keeps getting smaller and smaller because you're dividing the force through the tire by the area, and you just increased your contact patch. Your overall friction force for the tire is still the same. In this way, it doesn't matter how many cracks and crevices that your tire can grip on, because the more it can grip on, the less normal force it has to create friction at each of those. It's counter intuitive, but it's physics. Start melting tires, (not just hot and sticky, but literally melting them), and then you get into a whole different range of physics where surface area will matter. I would imagine professional racers find themselves skirting this line, but for the average rider, and even likely the average racer, this likely isn't the case. (sigh... this needs to be shown graphically and I just don't have the time)

dfox, you are correct...sorta. The contact patch doesn't make a difference, in an ideal physical world (image we have a spherical cow....).

In the real world, though, the physics is much more complex. Just like when you do idealized physics, a rock and a feather fall (are accelerated by gravity) at the same rate, but in the real world, well, things are complicated.

If you are doing high school, or even college level physics with calc, the mass of an object cancels out when determining how far something will slide with the coefficient of sliding friction. The real world, actually comes close to this, but even with a near ideal condition, like ice, it isn't precise.

The same is true with tires, contact patches, and roads. Do you think manufacturers put larger tires on sports cars and sportbikes just because they look cool? If not, think about the physics involved, and why the larger tire (and hence, larger contact patch) might make a difference, and where it might not.

I'm going to quote my physics prof here and 'leave it as an exercise to the reader'....

I will be happy to discuss it further though, from a pure physics point of view (in another thread if needed), but suffice to say here, that there is a reason (several, actually) that the contact patch makes a difference.

[Motofool]

Originally Posted by Worldtraveller

Interestingly, and I'm gonna go see if my google skills will find one, the actual traction 'circle' winds up being more heart shaped.

here: http://www.datamc.org/2013/05/28/x-y...action-circle/

Very interesting; thank you !!!

[Motofool]

Calculation of the reduction in bike's lean angle due to hanging-off:

As the angle of lean increases, that combined weight bike+rider grows up, but each weight, bike alone and rider alone, grows up in the same proportion.
For that reason, what the lateral relocation of the rider's CG achieves regarding the lateral relocation of the bike's CG is always the same, vertical or leaned.

It becomes a simple Seesaw problem: the lighter weight requires a longer lever respect to the pivot than the heavier weight, being the pivot the real and unique lean angle possible for that radius of turn and speed.

Rider weight/Bike weight = Bike lever/Rider lever

The most difficult variables to pinpoint with accuracy are the height of both CG's respect to the ground line that connects both contact patches.
Also, the contact patch location changes respect to the center-line of the chassis for leaned positions and more for wider tires.

Please, take a look at the schematics of these posts:
http://forums.superbikeschool.com/in...c=3324&p=26802

http://forums.superbikeschool.com/in...c=3303&p=26514

For Arctan calculation:
http://www.rapidtables.com/calc/math...Calculator.htm