Turns out that a skinny drag racing tire would work just as well on a top fuel dragster... for about ten feet, then the tire would overheat due to the lack of mass available to transfer heat away from the surface.

OK, sounds good. Thats all I need is a simple explaination. Hell, if I'm going to read a large excerpt like that.

That must be why MC track riders run slicks then. So they don't overheat. Otherwise why not put tread on them? It would be safer to have the dust and water shedding properties of tread if that were more important than max tire contact.

Hell, if I'm going to read a large excerpt like that.

but i do appreciate the backup.

Ain't this pertty?? New tires look so good i hate to ride on them. This is the smallest tread pattern I've ever seen on a street tire.

* Last updated by: Rook on 4/15/2012 @ 6:41 PM *

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hanging of the side is more than lean angle and contact patch, it is also a offset of weight and rider style

The ability to ride with extreme power then extreme braking, drifting in,then hanging off the side to counter the forces that want to go straight ahead,as well as squaring of the corner, has lead to the more extreme lean angles and greater hanging off.

If your hanging off and the bike is straighter up under acceleration, you can use the part of the tyre with the most rubber the centre, and use your weight to counter the mass wanting to go straight ahead

There is a point where power from the engine, will require a contact patch from a tyre made of the right materials to give enough grip to be effective. is this the reason the rear tyre is bigger than the front??

If contact patch doesn't matter because the weight is the same why do tyres at track days run lower pressures why is the rear bigger??

dry to wet tyres and type of rubber used,
Dry = slicks have no tread biggest contact patch used in the dry,
Wet = have tread pattern, same weight smaller contact patch with ability to clear excess water softer material will grip similar to dry but will wear out sooner

Its more than physics its an art form almost poetry

* Last updated by: ethin14 on 4/16/2012 @ 1:33 AM *

And what do those drag tires do in the first 10 ft or so?They stand up...become narrower....

Correct, lengthening the tire contact patch in the fore and aft direction which aids linear acceleration. They're not dummies that is for sure.

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If contact patch doesn't matter because the weight is the same why do tyres at track days run lower pressures why is the rear bigger??

Contact patch does matter, just not for the reason everyone assumes. It has more to do with tire wear rates and heat management than absolute traction.

Bigger tire in the rear because it's getting a high power loading which the front doesn't get, heat management again maybe? Lower tire pressures allow the tires to conform to surface imperfections in a real world road surface?

Look at the guys on literbikes who have switched from a 190/55 profile tire to a 180/55. They don't seem to lose any straight line traction from the smaller tire contact patch and the handling gets much quicker due to the 180s shape. the tire does wear out a lot quicker though.

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That must be why MC track riders run slicks then. So they don't overheat. Otherwise why not put tread on them? It would be safer to have the dust and water shedding properties of tread if that were more important than max tire contact.

I would venture to say that slicks for dry track conditions has as much to do with lowering the wear rate on the tire as anything.

Those racing slicks are gummy bear soft rubber to get a high coefficient of friction, they don't last long and need all the help they can get. More tread = more wear

How many times have you heard about racer X setting a blistering lap pace early in a race and then slowing dramatically because his tires "went off". High stick must be balanced with good wear rates or you don't finish races, large contact patch gives you good wear rates and heat management.

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same weight smaller contact patch with ability to clear excess water softer material will grip similar to dry but will wear out sooner

There ya go!

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Ain't this pertty??

Dis iz pertier, IMHO.

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Lower tire pressures allow the tires to conform to surface imperfections in a real world road surface?

That would be the same as maintaining a larger contact surface.

My thought is that reducing the air pressure is a way way of maintaining proper tire pressure when the tire is hot. A race track tire gets so hot that the internal pressure increases too much. By the time the tire heats up to track temp, you are actually running on a tire that is overinflated. Using 33% lower than specced inflation makes tire pressure about right when the tire gets up to track temp. This makes such a huge difference that I noticed instantly on my second or third track session. I was not even having a problem cornering. It was a serious problem in straightline braking that got my attention.

So ASFA tire inflation goes, we are back to heat management. The tire gets too firm and has less contact patch which causes the tire to be too hot and that makes it slippery? I'll go with that but good old "more contact patch = more grip" sure sets better in my mind. I never saw my tires melt on the street and I often overinflate them for street use.

That's not perty, that's SICK!

here's mine.

* Last updated by: Rook on 4/16/2012 @ 9:51 AM *

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"more contact patch = more grip" sure sets better in my mind.

You are correct Rook, that's exactly how it works, also the rise in temp is already catered for in the design and setup of tyre and pressure

The reason the rear is bigger is it has to transmit all the power and torque of the engine to forward movement.

The rear contact patch is constantly changing, when at rest the weight on it is constant,it would be at its smallest as the torque of the engine turns the wheel the tyre grips, and the hole dynamics of the suspension comes into play as the weight transfer begins to take effect, lifts up at front and down on rear there is now more weight on the rear wheel and creates a larger contact patch providing more grip

Thats why you lower tye pressure for more grip

With the drag car this is why the rear tyres are so big and same with bikes as the weight transfer happens on a hole shot of the line you have more weight to push down on that tyre and make a bigger contact patch and more traction, reason you have spoilers and aerodynamics in play also. Tyre Dia when standing up is also about ratios but that's another mater

* Last updated by: ethin14 on 4/16/2012 @ 6:32 PM *

He's right, you are correct and the vast body of scientific evidence gathered over the last five hundred years that has determined that you are both wrong is all nonsense. I'm done wasting my time here.

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Laws of Friction, with Applications to Motorcycling

First Law of Friction
We all think we know how friction works. But pick up a physics book such as Fundamentals of Physics by Halliday, Resnick, and Walker, or a book such as Friction by Bowden and Tabor, and read the two laws of friction and you'll get a surprise. The first law is easy to believe: The friction between two surfaces is proportional to the force pressing one to the other. This force could be the weight of a motorcycle pressing the tire into the pavement, or the clamping force pressing two pieces of wood together. "Proportional" just means that if you double the pressing force you double the friction.

The second law is where all the trouble starts. To understand it, suppose you set up an experiment. You put a brick on a table and investigate how much force it takes to start the brick sliding. You screw an eyebolt into the brick, run a line from the eyebolt to a pulley on the edge of the table, and then attach weights to the end of the line. You add weight until the brick starts to slide.
Second Law of Friction
Now here's the interesting part, and the surprising part. You would notice that the orientation of the brick doesn't make any difference. That is, the friction is the same whether the brick is on its large face, the smaller side, or the small end. The friction is independent of the contact area.

Don't believe it? You're not alone. Bowden and Tabor, in their book Friction , tell about one of the first modern investigators of friction, Guillaume Amontons. In 1699 Amontons published a paper on friction in which he reported on the two laws. As Bowden and Tabor put it, "The second law, that friction is independent of the size of the bodies, was viewed by the [French Royal Academy of Sciences] with astonishment and skepticism. They instructed their senior academician De la Hire (1640-1718) to repeat Amontons' experiments and check their validity. This he did and confirmed Amontons' conclusions. Amontons' laws of friction have remained with us to this day as a very good working approximation."
I still don't believe it.
It'd probably be less counterintuitive if we could see the microscopic texture of surfaces. Imagine a flat perfectly smooth metal plate. It's flat and perfectly smooth, right? If you think so, you've never seen a micrograph of a flat perfectly smooth plate. It's actually scratched and pitted, like a mountain range in the small.

Now imagine a couple of mountain ranges on plates. Turn one over and put it onto the other. The actual contacts will be parts of the various peaks of the two plates onto whatever part of the other plate happens to match the peak. Those peaks — asperities, the tribologists call em — are where the friction occurs, not, obviously, in the valleys where there is no contact. Press em harder and you'd get more actual contact as the asperities bend under the pressure.

If you take another pair of mountain ranges/plates of twice the area and pressed them together with the same pressure, the actual contact area of asperities wouldn't change. You'd have the same number of asperities in contact, but further apart, in the larger plates. Only additional pressure would change the true contact area.

That, in a nutshell, is the model that people use to make sense of the experimental fact that F=?N: friction F is proportional to the force N pressing two surfaces together, with proportionality constant ?. (Apparent) area of contact does not enter into it.
Does this really apply to rubber?
Sometimes people object that the above model may be satisfactory for rigid materials like metals, but rubber would flow into the valleys and you'd get better contact. They miss the fact that rubber at the microscopic scale is quite as irregular as metals are. Pressing rubber onto an irregular surface such as pavement will indeed result in greater area of actual contact (as opposed to the apparent macroscopic area) than might be the case with a metal on pavement, but that contact is still between irregular surfaces; there will still be plenty of gaps in contact. Reducing the gaps can be achieved by pressing harder, which will result in more friction — just as the equation F=?N predicts.

That's the model, anyway. How well does it match the reality of rubber friction? A careful reading of Robert Horigan Smith's book Analyzing Friction in the Design of Rubber Products and Their Paired Surfaces (2008, CRC Press) appears to indicate that rubber friction has more components than the single one of adhesion, which is what F=?N models, but that any departures from that model are minor and lost in the noise of real-world tires and pavement. Smith analyzes the published literature of rubber friction and concludes that rubber friction arises from 4 sources. One is due to the wear of the rubber, which is undetectable in non-sliding situations such as tires rolling on pavement. Two others he calls microhysteresis and macrohysteresis, which arise from the not-quite-elastic deformation of the rubber. They are very minor in comparison to the fourth source, adhesive friction, just what is modeled by the above two classical laws of friction.

Smith argues that engineers concerned with rubber friction — tires, shoes, automotive fan belts — who neglect the hysteresis forces are missing a significant design tool. But by far the dominant contributor to tire friction is adhesion, which is well-described by the two classical laws of friction: It's proportional to the force pressing the rubber to the road, and independent of apparent contact area.
Application of the First Law
With this information and no more, we can understand two important facets of motorcycle operation. The first law, that friction (which we call traction in the context of tires on road) increases as weight increases, explains why the front brake on a motorcycle (and a car for that matter) is so much more effective than the rear brake. As you slow a vehicle, the weight transfers to the front. We all recognize this; it's why the bag of groceries on the seat slides onto the floor when you get hard on the brakes. So the front tire is now carrying more load than it was; thus it now has more traction than it did. The opposite is happening at the rear: The rear tire is now lighter than it was, and so has less traction. The harder you brake the more the weight and hence the traction transfers forward.

Application of the Second Law
Everyone knows that you have less traction in a lean than when the motorcycle is straight up and down. This is because, in a lean, there's less rubber on the road.

Right? Well, if you've been paying attention, you'll realize that what everyone knows, is wrong. The second law says that friction is independent of contact area. That implies that, if the traction is indeed less, it isn't because there's less rubber on the road. The second law says that the amount of rubber on the road is not relevant. (It's interesting to me that people who know what everyone knows always overlook the fact that there isn't less rubber on the road in a lean. Motorcycle tires are round. The amount of rubber on the road is the same whether the motorcycle is straight up and down or leaned over.)

So what everyone knows about why there's less traction in a lean, is wrong. Maybe everyone is wrong about the reduced traction as well? They are. The first law says that the friction between two surfaces is dependent only on the force pressing them together; in our application, that's the weight of the motorcycle. Does the motorcycle weigh less in a lean than straight up and down? Of course not; if that were true, we could lose weight simply by leaning over.
Ok, so we've concluded that the amount of traction in a lean is exactly the same as when straight. So what's the origin of this myth? It's certainly true that if I'm leaned far over and apply much braking I'll lose traction and slide. What's the deal, if there's just as much traction in a lean as straight? The explanation is that one's available traction has to be shared between the various users of traction. The Motorcycle Safety Foundation has a good image in their experienced rider course book. The total traction available is represented as an oval or circle, and the things which use traction are partitioned in it.

So with this in mind, it's not hard to understand why we can't brake hard while in a lean. When cornering hard, most of our traction is being used for turning, with some for acceleration, and little or none for braking. The diagram looks like this:

The size of the circle is the same because we have the same amount of traction as we did while straight, just as the first law requires. Much of our traction is used in cornering. There's some used in accelerating, if we're on the gas through the curve. Drag at the wheels is always present so I've represented a small amount of traction for that. So what's left over, the white "reserve" sliver, represents all the traction that we have to work with for any emergency, such as braking for an unexpected obstacle or because we went into the corner too fast. It is the small size of the reserve which gives rise to the myth that traction is lacking in curves. Or, if you prefer, it isn't a myth, merely worded differently. The traction which one has to work with in curves is much smaller than that available in a straight line.

Objection!
So if traction doesn't depend on amount of rubber, how come high-performance tires are so large? Hunh?

To understand this, we have to make the first law more precise. The friction between two surfaces is proportional to the force pressing them together. But the friction between these two surfaces can be quite different from the friction between these other two surfaces, even if the force on them is the same. It's easier to slide a steel plate on pavement than a rubber tire on pavement, even when both are loaded with, say, 5 pounds.

The two laws can be combined into a single equation: F = ?W, where F is the friction between two given surfaces, W is the force pressing them together (the weight, in most of our examples), and ? (the Greek letter mu) is a number called the coefficient of friction. This equation says that the friction is a percentage of the total weight on two surfaces, the percentage being given by the coefficient of friction. (That's really just the first law, saying that the friction is proportional to the weight, the constant of proportionality being given by ?. The second law is incorporated by the fact that the area of contact does not appear in the equation.)

The fact that some surfaces are "stickier" than others is reflected in the different coefficients of friction. Steel on pavement has a much lower value of ? than rubber on pavement. And what's more, different rubber compounds have different values of ?. You want more traction? Just use stickier rubber in your tires. A further complication is that the coefficient of friction varies with various physical parameters. For instance, cold rubber is harder and thus less sticky than warm rubber; the same equation applies but ? is lower for the cold rubber. Static friction, the force necessary to start sliding, is greater than the friction created while sliding. In riding, we're concerned with rolling friction, which is somewhere between static and sliding friction. Again, same equation, but three different values of ?.

If you switch to tires with a better coefficient of friction, you'll immediately notice that stickier rubber is also softer; it wears out much more quickly. Motorcyclists accept the need to replace high-performance tires more often than touring-oriented rubber, but the auto types have another option: They can use wider tires to spread the wear over more rubber. And there, finally, is the reason high-performance auto tires are wider. It isn't to get better traction. Better traction comes from stickier rubber. The tires are wider to get acceptable wear from the stickier, softer rubber. (As well as for other things like heat management, rigidity under the stresses of cornering and braking and acceleration, etc.)

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Everybody knows that you pick up a motorcycle(decrease lean angle) to get a wider contact patch for better traction right........ wrong again!

* Last updated by: Kruz on 4/16/2012 @ 8:14 PM *

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made it about half way through.

This could have been a much shorter thread if that excerpt was posted at the beginning instead of a math problem that 98% of us had no clue of what it meant let alone how to solve it.

Now imagine a couple of mountain ranges on plates. Turn one over and put it onto the other. The actual contacts will be parts of the various peaks of the two plates onto whatever part of the other plate happens to match the peak. Those peaks — asperities, the tribologists call em — are where the friction occurs, not, obviously, in the valleys where there is no contact. Press em harder and you'd get more actual contact as the asperities bend under the pressure.
If you take another pair of mountain ranges/plates of twice the area and pressed them together with the same pressure, the actual contact area of asperities wouldn't change. You'd have the same number of asperities in contact, but further apart, in the larger plates. Only additional pressure would change the true contact area.

That's all we need to know. your tires have a hundred bumps touching the road and a hundred valleys not touching the road. Increase the contact patch and you have the same # of bumps touching but they are dispersed over a larger area. Makes sense. Still hard to accept when i think of the way rubber behaves on the macro level. It bends around things so it seems that it would grip onto more surfaces if it had more surface to grip.

....then again, when I envision a flat surface (flat in the macro world cuz we know flat is non-existant in the micro world) I can see that if a 200 lb guy balances on tip toe in a 4 inch square of rubber, it will take say 400 lbs of force to drag that rubber across a cement floor. I could prolly drag him with a quadriceps extension if I used all my strength and had some sort of horizontal slide squat machine like they have in the gym.....just need to hook a cable up to it.

Now put the same 200 lb guy on a 4 foot square of rubber on the same cement floor. Same squat machine. I'd jump in there and do it again same as before. OK Kruz now I believe it. My 190 55 is just to blow absorb and dissipate more heat. Never would have guessed.

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looks a lot nicer too, IMHO.

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.....we still don't know why a tire with less internal pressure grips better. It really does. I do not notice a dif on the street but the dif was HUGE on the track. I went from almost killing myselfon on T5, literally going off into the grass one time, to cornering with relative ease at about twice the speed.

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He's right, you are correct and the vast body of scientific evidence gathered over the last five hundred years that has determined that you are both wrong is all nonsense.

That's quite a dummy spit there Kruz , sorry that rook and I are not intellectually gifted math geniuses like you
we appreciate your contribution to last 500 years of science.

I'm done wasting my time here

sorry you consider us a waste of time, I read my post again an can't see where I offended you.
I may well be wrong you could of said where,

but will delete the post if you want and except everything you click and paste to be true

sorry for the debate

God bless

well, Ethin., I'm accepting it as gospel. I think a teacher brought the topic up way back in 4th grade. Mr DeMerse. Its a dusty old memory (not quite 500 years).

BUt I'm still lowering my tire pressure to 28 lbs on Wednesday. ...assuming it isn't pouring pitchforks. What works in when you actually do it, that is always the last word isn't it? If something works but it's not supposed to I don't usually ask why, I just do it.

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WOT happens after 50 degrees?
Nevermind... I know.

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WOT happens after 50 degrees?

The coefficient of friction is still in play.

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The coefficient of friction is still in play.

LMAO!

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".....we still don't know why a tire with less internal pressure grips better".....does it grip better?Or is it because there's more surface area to contact the road?...and you mentioned about T5 and all...is it possible that you felt more comfortable after a while?IDK.....maybe just the 'thought' that it was going to BE better actually caused you to stop sweating the 'danger',and believe that it actually WAS better,which made you actually RIDE better.Could that be? Things work in strange ways sometimes.

One reason I don't like listening to naysayers.Regarding almost any subject.I've pretty much felt over the last several years of riding that thinking about failing is a real block to actually succeeding at riding and having fun.It'
s kinda like....'if you focus on that object in your path...you'll hit it"...that kind of thing.Riding a bike(for me)has definitely been a learning experience for sure.I mean...a fast strong bike.

* Last updated by: Grn14 on 4/16/2012 @ 10:54 PM *

can't argue with the maths, but after racing for nealy 40 years cars and bikes I know this.

If I let the tyre pressure down it will give more grip.

I always believed it was because the contact patch was bigger and the rubber conformed to the surface better and with weight transfere would give better grip.

I maybe wrong

The science may say other wise, this still remains unansered as to why.

".....we still don't know why a tire with less internal pressure grips better".....does it grip better?Or is it because there's more surface area to contact the road?...and you mentioned about T5 and all...is it possible that you felt more comfortable after a while?

Oh yes Grn, it DOES grip better no doubt about it. This was going into turn 5 braking at max, not in the turn leaned over at all . max brake, rear wheel up swishing back and forth. It even was happening with hard downshifting. No real cornering skill involved yet. NOPE, that sucker stuck like glue after I dropped the pressure to 28 lbs. Could not have been mind over matter, it just had a lot more grip and this was straightline braking performance, not cornering acceleration (which is where you would expect there to be more of a problem.

On the street, I really don't notice any change in grip with low tire pressure but to me, it does feel kind of unpredictable and squishy when I turn in. NO like for street.

.'if you focus on that object in your path...you'll hit it"...that kind of thing.

Yes exactly. pondering these things becomes overthinking which can become counterproductive at some point. Yeah we have many years to learn this stuff . No need to know everything right now.

can't argue with the maths, but after racing for nealy 40 years cars and bikes I know this. If I let the tyre pressure down it will give more grip.

Same here. It makes a huge dif to me on the track. It works so well, why stop? Be nice to know why it works but I won't lose sleep over it. I'll just keep doing it. The scientists all agree on friction and contact area, the racers all agree on traction and tire pressure. No reason to argue that.

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No one's mentioned suspension yet.Just a softer rear tire.You said in a straight line there Rook...you had a big difference when you changed pressure.Downshifting,braking.Both of those cause weight to unload off the rear...you know that.Could it be....the now lowered rear tire pressure is acting more like a shock absorber than a fully dedicated rolling tool?IDK.Lots of variables in what you're saying.

I can say this...Kawasaki upgraded the suspension on the new bike.Added a slipper.At highway speeds(any really) and with 42psi...the recommended amount...I've experience so far virtually NO tire hop,or skid from high rpm downshifting...OR 'harder' braking.So I don't know what really to say about PSI's...Those race tires do react differently with those speeds...and ya gotta remember...even though we 'want' it to be...the zx14,earlier OR late models are not dedicated track bikes.Their main purpose is....sport touring and Dragstrip performance...not tight fast twisties.Just too much weight to throw around and get 1000 or 900 or 750 bike performance out of em.No one with the Ohlins setups here has ever really commented on how their 'new' suspension does at any track.So it's very hard to know IF the Ohlins or whatever have actually bettered the track manners of the 14.

I used to get regular tire hop and stuff from my other 14...downshifting and hard braking...this new one....it works VERY nicely.