Bike Tire Basics

This could be the first in a group of articles exploring motorcycle tire basics and various basic powerful characteristics of the particular handling behavior associated with motorcycles. Overall this particular is an extremely complex subject
and needs a good degree of mathematics and even physics effectively understand what's happening.
On the other hand, in these content I'll try in addition to explain the basics with the complete minimum of mathematics,
but where this specific is unavoidable I will not go above basic trigonometry. For those that are disappointed
with any arithmetic whatsoever, don't worry, just skip individuals parts and the particular rest should still prove useful.
Items try and illustrate the mechanics numerous sketches and chart.

It seems outstanding that just two small contact patches of rubber, can easily support our devices and
are able to deliver large amounts of power to typically the road, whilst in the same time supporting handling
forces at least around the weight of the bike and rider. Consequently the particular tires exert possibly the single
most important influence over common handling characteristics, therefore it seems appropriate to study their
characteristics ahead of the other various areas of chassis design.
Any time Newton first expounded to the world his theories of mechanics, no doubt he had on his mind,
things apart from the interaction of motorbike tires with the particular terrain. Never-the-less his / her
suppositions are both equally valid for this kind of situation. In particular his / her third law declares, "For every pressure there
is definitely an equivalent and opposite power to resist this. " as well as to put it another method "Action and reaction are equal and even
opposite. "

Related this to wheel action, means that when the tyre is pushing while travelling then the highway is pushing
again equally hard about the tire. This applies equally good regardless of regardless of whether our company is looking at
supporting the weight associated with the bike or perhaps resisting cornering, braking or driving loads.
What this special law of Newton would not concern itself with, is which often force is typically the originating one neither
indeed does it subject for many purposes of analysis. However, being a guide to typically the comprehension of
some actual physical systems it will be often useful to mentally separate typically the action from the particular reaction.
The forces that occur involving the ground plus the tires determine a great deal the behaviour of our
machines, but these people are so frequently obtained for granted. four tires really perform these kinds of a multitude of different
duties and their apparent simplicity hides the level of engineering style that goes straight into their
design and fabrication. Initially pneumatic tires were installed to improve comfortableness reduce loads about
the wheels. Even with modern suspension devices it really is still typically the tires that give the first brand of
defence for soaking up road shocks.
To learn carcass construction, tread compound and proceed pattern in excellent detail is beyond the scope
with this book. Rather we are concerned here with some basic principles and even their effects in handling
characteristics.

Fat Support

The obvious functionality of the wheel is to support the of the machine, whether straight or
leaning more than in a nook. However , the genuine mechanism with which the air pressure in addition to tire passes
the wheel load for the road is usually misunderstood. Consider fig. 1, this draw represents a cut
throughout the bottom regarding a rim and tire of unit thickness with a pumping pressure of S. The left
section shows the tire unloaded plus the proper hand side exhibits it supporting typically the weight F. If
loaded the car tire is compressed vertically and the breadth increases as proven, perhaps surprisingly the
internal air stress does not transform significantly with insert, the internal volume is definitely little changed.
From the widest area (X1) with the unloaded tire the interior 1 / 2 width is W1, and so the particular force normal to be able to
this section due in order to the internal pressure is simply two. P. W1. This kind of force acts up wards on the wheel
rim, but since the stress and tire width are equally distributed across the area the overall
effect is completely balanced. This force likewise has to be opposed by an equal tension (T) within the tire
carcass.

The loaded tire contains a 1 / 2 width of W2 at it's widest section (X2) plus so the regular force is a couple of. P. W2.
Therefore, the excess force over it, when loaded, is 2. L. (W2 - W1) but as the wheel is just
widened over a small section of the bottom part area of the circumference, this particular force supports the load F.
Typically the above describes how a inflation pressure and tire width raise produce forces in order to oppose the
straight wheel loading, but does not completely make clear the detail of the mechanism by simply which these
causes are transferred in order to the rim. The bead of the fitted tire is an interference fit the bead seat of
the tire rim, which puts this area straight into compression, the in-line component of the side-wall tension
due in order to the inflation stress reduces this compression setting somewhat. This aspect is shown while F1 on
the unloaded half of F1 = T. cos(U1). The higher angle U2 of the side-wall if loaded means
that the in-line component of the strain is reduced, thus also restoring a number of the rim to tyre
bead compression. This kind of only happens in the lower part of the tire circumference, where the extending
takes place. So there exists a nett rise in the compressive force on the reduce rim acting way up, this
supports the particular bike weight. The particular nett force will be the difference in between the unloaded plus loaded in-line
forces,

F = To. (cos( U1) -cos(U2))

The left edge displays half of a great inflated but
not loaded tire, an anxiety (T) is made within the carcass simply by
the interior pressure. In order to the right, the particular compressed and even
increased shape of typically the loaded tire is usually shown.

Suspension Action

In performing this function the pneumatic tire is the first object that will feels any highway shocks and therefore acts
as the most significant element in the machine's suspension system. For the extent of which, while
uncomfortable, this would be quite feasible to drive a motorcycle around typically the roads, at reasonable speeds without
various other form of bump absorption. In reality rear suspension was basically not in any way normal until the nineteen forties or 50s.
Although, regardless of typically the sophistication of the conventional suspension system, it would be quite
impractical to make use of wheels without pneumatic tires, or several other form of tire that authorized
considerable bump deviation. The loads provided into the wheels without such four tires will be enormous from
basically slow rates, and continual steering wheel failure would get the norm.
Several figures will demonstrate what I lead to: --Assume that the motorcycle, with a typical size front steering wheel, hits a 25
logistik, sharp edged bundle at 190 km/h. This not a huge bump.
Without wheel the wheel might then be theme to an regular vertical acceleration associated with approximately
1000 Gary the gadget guy. (the peak value would be greater than this). This method than if the wheel and braking system
assembly had a mass of 25 kilogram. then the typical point load within the rim would be 245 kN. or even about 25
lots. What wheel could stand that? When the wheel has been shod which has a normal tire, then this would certainly have at
walk out, a spring rate, to a sharpened edge, of around. 17-35 N/mm. TypicallyGo to the website
transmitted towards the tire for a twenty-five mm. step can be about 425-875 And. i. e. below four thousandths
with the previous figure, and also this load would end up being more evenly spread across the rim. Without the tire typically the
shock loads exceeded back to typically the sprung part associated with the bike would certainly be much better too. The straight wheel
velocity would likely be greatly greater, and so the particular bump damping causes, which depend about wheel
velocity, would be tremendous. These types of high forces would be transmitted directly back in bike and driver.
The following 5 charts show a few outcomes of a computer simulation of accelerations and
displacements upon a typical path motorcycle, and show the tire's significance to comfort plus road
holding. The particular bike is traveling at 100 km/h. and the front side wheel hits some sort of 0. 025 metre high step with 0. 1
secs. Note that the particular time scales vary from graph in order to graph.
Three cases are considered:

With typical straight tire stiffness and typical suspension cropping and damping.

With identical tyre properties but together with a suspension spring rate of one hundred X those of the previous.

Together with tire stiffness hundred X the preceding with normal suspension system springing.

So essentially our company is considering some sort of typical case, an additional case with almost no suspension cropping and
the final case is using a virtually rigorous tire. Structural loading, comfort and roadholding would all become adversely
affected with out the initial shock absorption of the tire. Remember that the above charts are certainly not most to the same amount of time scale,
this is simply to better show the right points.

This specific shows the top to bottom displacement of the particular front wheel. There is little big difference between the maximum
displacements for the particular two cases along with a normal tyre, for a compact step the top tire absorbs almost all of the surprise. Yet ,
in the case of a very stiff tire, the wheel activity is increased by a factor of approximately 10 times. It is obvious of which the tire
results in the ground in this case as well as the landing bounces is seen after 0. a few seconds.

These shape show the up and down movement of the particular C of Gary the gadget guy of the motorcycle and rider. As with Fig 1 its clear that typically the stiff tire
reasons greater bike moves, towards the obvious detriment of comfort.

Representing the various accelerations transmitted for the bike and even rider, these figure demonstrate vertical
accelerations at the C involving G. Both associated with the stiffer car tire or stiffer postponement, interruption cases show related values of about a few or 6 periods
regarding the normal case, nevertheless the condition of the a couple of curves is very different. With the hard suspension there exists minor
damping and that we can easily see that this uses a few process to be in down. Typically the second bump at around 0. one hundred fifty five seconds is when the
rear wheel hits the action, this rear wheel response is not necessarily shown on typically the other graphs with regard to clarity.

Front steering wheel vertical acceleration to the two cases with a normal tire. The early part is comparable for the two situations,
the suspension features little effect here, it really is tire deflection this provides the most important for this height of step. Just as Fig 5 typically the
lack of suspension system damping allows the tire to jump for a few cycles prior to settling down.

Because in these curves are in the tire acceleration, the ideals of the normal case are overwhelmed by the stiff
tire case, with a peak worth of close to be able to 600 G in comparison with nearly 80 G normally. Once again note the consequences of the landing
bounces right after 0. 5 secs. This high velocity would cause really high structural loading.

As the tire is really good from removing the majority of the road shocks, right at the particular point of software, perhaps it
can be worth while to be able to consider designing that to absorb more and eliminate the particular requirement of other
postponement, interruption. Unfortunately we might run into some other problems. We have all seen big construction
machinery jumping down the street prove balloon tires, sometimes this gets so violent that will the
wheels actually leave the land. Some sort of pneumatic tire acts just like a great air spring, as well as the rubber acts seeing that
a damper any time it flexes, yet when the tyre is made bigger the springing effect overwhelms the
dissipating and then find the uncontrolled bouncing. So you can find sensible restraints to the sum of
cushioning which can be built into a tire for virtually any given application.

Effects of Tire Pressure

Obviously, the springing characteristics mentioned over are largely affected by the tyre inflation
pressure, although there are some other influences also. Carcass material and construction as well as the properties
and tread pattern involving the outer level of rubber most have an impact on the springing properties plus
typically the area in speak to with the earth (contact patch). Under and even over inflation each allow the tyre in order to
assume non-optimum cross-sectional shapes, moreover the inflation pressure exerts an affect
over the spectrum of ankle flexibility of a tire and this kind of is a real estate of the maximum importance to motorbike
stability. Manufacturers' tips should be adhered to be able to.

The influence of tire pressure on the subject of the vertical rigidity of an inflated tire, when packed upon
a toned surface. These curves are from genuine measured data. Note that the springtime rate is near to
linear over the full range of loading and varies from 14 kgf/mm. in 1. 9 bar pressure to nineteen kgf/mm. from
a couple of. 9 bar. The particular effective spring price when the tire is loaded towards a sharp border, for instance a brick, is definitely
considerably lower as compared to this, and it is a lot more non-linear due to the altering shape of typically the contact area since
the tire "wraps" around the item.

This spring charge acts in collection together with the suspension suspension systems and is an essential part of the particular overall
suspension technique. An interesting home of rubber is the fact that when compressed and released it
will not usually return exactly to it's authentic position, this will be generally known as hysteresis. This effect is displayed
just for the a single. 9 bar. situation, the curve attracted through the loading cycle is simply not followed during the
unloading stage. The area among these two shape represents a loss of energy which usually results in
tire heating and likewise acts as a kind of suspension damping. With this particular case the energy lost
over one loading and unloading cycle is approximately 10% of the total stored energy in the
compressed tire, and is definitely a substantial parameter managing tire bounce.

Directory stiffness of some sort of standard road tire against a flat surface area at different inflation pressures. This files is from an
Avon Azaro Sport II 170/60 ZR17. The particular upward arrows indicate the compression involving the tire plus the 2nd line together with the
downward arrow (shown only at one 9 bar for clarity) shows the particular behaviour of the tire when the particular load is introduced. The
shaded area between the 2 lines represents a loss of power called hysteresis. This kind of provides for a source associated with suspension
damping and even also heats the tire. (From files supplied by Avon tires. )

Spectrum of ankle stiffness of typically the same tire demonstrated in fig. nine. The vertical load was constant with 355 kgf. along with the wheel was
retained vertical. As anticipated the tire is usually somewhat stiffer with the higher pumping pressure but seems to lose grip or saturates at the
more affordable lateral load of 460 kgf. in comparison to 490 kgf. on the lower pressure. (From data supplied by simply Avon tires. )

Contact Area

The particular tire must eventually give it's help to the bike all the way through a small place of rubber in contact with the
ground, therefore "contact patch area = vertical force average make contact with patch surface pressure". This
applies under ALL conditions.

The contact spot surface pressure is simply not however, the same as the pumpiing pressure, as is
sometimes claimed. They are related nevertheless there are no less than four factors which often modify the partnership.
Carcass stiffness, body shape, surface plastic depth and real softness, and road surface area compliance. If
all of us have an extremely high carcass rigidity then inflation pressure may have a decreased influence.
Let's appear at this found in a little more detail in addition to see why:

In case a tire was made just like the inner tube, of which is from quite thin rubber and with little tightness unless
inflated, then the internal air pressure might be the just means to support the particular bike's weight. Inside of this
case the contact patch stress would be equal to that of typically the internal air pressure. For an air
pressure of two bar and a vertical load regarding 1. 0 kN. Then the speak to area would end up being 5003 sq mm. If we
at this point increased the surroundings pressure to say 3 bar the particular area would slide to 3335 sq . mm.

Let's at this point imagine that we substitute a rigorous steel tubular hoop for our rim in addition to tire, the place in contact
with all the ground will be quite small. If we now increase the hoop with an air pressure, keep in mind that take
much imagination to see that, as opposed to the inner conduit, this internal stress could have a minimal impact
on the external portion of make contact with. Obviously, a tyre is not very much like the steel hoop, nor the interior tube,
but this specific does show that the carcass rigidity can reduce typically the contact surface area as calculated solely
from inflation pressure alone.

I did 2 sets of tests. For the very first I kept the tire inflation pressure constant at 2 . 4 bar in addition to varied the wheel
load between 178 and 1210 N. (allowing for the weight of the particular glass and wooden beams). Secondly, I
keep a consistent fill of 1210 D. and tried different the inflation stress between installment payments on your 5 to 1 watering hole.
Even with a generous allowance for experimental error typically the effects are clean. The graphs show that
the outcome made an appearance to fit realistically well to a smooth line, presently there wasn't much scatter.

Point (1) in the curve together with constant inflation pressure, shows the way the actual contact patch stress is
lower (just over half) compared to the inflation strain, or in some other words the speak to area is increased. This is
as a result of rubber surface compliance, thus this is more important