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This will be the first in a series of articles exploring motorbike tire basics and even various basic powerful characteristics of the handling behavior regarding motorcycles. Overall this particular is an extremely complex subject

and needs a good degree of mathematics and even physics to properly understand what’s happening.

However, in these content articles I’ll try plus explain the basics with the complete minimum of math,

but where this specific is unavoidable I will not rise above easy trigonometry. Continually are unhappy

with any arithmetic whatsoever, don’t be anxious, just skip those parts and the rest should even so prove useful.

I am going to try and show the mechanics with many sketches and graphs.

It seems amazing that just two small contact sections of rubber, can support our equipment and

are able to supply large amounts involving power to the road, whilst at the same period supporting cornering

pushes at least around the weight associated with the bike and rider. Therefore the particular tires exert probably the single

most critical influence over basic handling characteristics, therefore it seems appropriate to examine their

characteristics prior to the other various aspects of chassis design.

Any time Newton first expounded to the planet his theories involving mechanics, no uncertainty he had in the mind,

things apart from the interaction of motorbike tires with typically the road surface. Never-the-less his / her

suppositions are both equally valid for this particular situation. Especially the third law claims, “For every push there

is an equal and opposite push to resist this. ” as well as to set it another method “Action and effect are equal in addition to

opposite. ”

Pertaining this to tire action, means of which when the tire is pushing while travelling then the highway is pushing

back equally hard about the tire. This applies equally well regardless of no matter if we are looking at

supporting the of the bike or even resisting cornering, brake or driving lots.

What this specific law of Newton will not concern itself with, is which in turn force is the originating one neither

indeed will it issue for many factors like analysis. However, as being a guide to typically the knowledge of

some bodily systems it will be often useful in order to mentally separate the action from typically the reaction.

The makes that occur in between the ground plus the tires determine so much the behaviour of the

machines, but that they are so often used for granted. auto tires really perform such a large number of different

responsibilities and their apparent ease hides the degree of engineering style that goes straight into their

design plus fabrication. Initially pneumatic tires were built in to improve comfortableness reduce loads about

the wheels. Even with modern suspension techniques it truly is still the tires that offer the first type of

defence for ingesting road shocks.

To learn carcass construction, stand compound and stand pattern in great detail is past the scope

on this book. Rather we have been concerned here which includes basic principles plus their effects in handling

characteristics.

Excess weight Support

Raising purpose of the exhaust is to assistance the weight of the machine, whether up-right or

leaning over in a corner. However , the actual mechanism by which the air pressure and even tire passes

typically the wheel load for the road is frequently misunderstood. Consider fig. 1, this drawing represents a cut

throughout the bottom involving a rim and tire of unit thickness by having a pumping pressure of S. The left hand

part shows the wheel unloaded along with the correct hand side displays it supporting the weight F. Whenever

loaded the tyre is compressed top to bottom and the size increases as demonstrated, perhaps surprisingly typically the

internal air stress does not modify significantly with load, the internal volume is little changed.

At the widest section (X1) with the unloaded tire the internal fifty percent width is W1, and so the particular force normal to be able to

it due to be able to the internal strain is simply a couple of. P. W1. This specific force acts upwards on the wheel

rim, but as the strain and tire width are consistently distributed around the area the overall

result is completely balanced. This force furthermore has to become resisted by the same pressure (T) within the car tire

carcass.

The filled tire contains a 50 percent width of W2 at it’s greatest section (X2) and so the regular force is two. P. W2.

Therefore, the additional force more than it, when loaded, is 2. P. (W2 – W1) but since the wheel is just

widened above a small part of the bottom part portion of the circumference, this force supports the particular load F.

Typically the above describes the way the inflation pressure and tire width boost produce forces to oppose the

top to bottom wheel loading, although does not completely explain the detail regarding the mechanism simply by which these

causes are transferred to the rim. The particular bead of a new fitted tire is usually an interference fit over the bead chair of

the steering wheel rim, which positions this area straight into compression, the in-line element of the side-wall tension

due in order to the inflation strain reduces this compression somewhat. This component is shown because F1 on

the unloaded half regarding F1 = T. cos(U1). The increased angle U2 regarding the side-wall when loaded means

that the in-line component associated with the strain is reduced, thus also restoring a few of the rim to tire

bead compression. Tyres In Reading happens within the lower part regarding the tire circumference, where the extending

takes place. Thus you will find a nett raise in the compressive force within the decrease rim acting upward, this

supports typically the bike weight. The nett force is definitely the difference between the unloaded and loaded in-line

causes,

F = Capital t. (cos( U1) -cos(U2))

The left hand side indicates half of a great inflated but

not loaded tire, a stress (T) is made inside the carcass simply by

the internal pressure. To be able to the right, the particular compressed and

increased shape of the loaded tire will be shown.

Suspension Action

In performing this function the pneumatic tire is the particular first object that will feels any street shocks and so acts

as the most significant element in typically the machine’s suspension program. Towards the extent of which, although

uncomfortable, it would be quite feasible to ride a bike around the particular roads, at sensible speeds without

additional form of lump absorption. In fact rear suspension was basically not in any way commonplace until the nineteen forties or 50s.

Although, regardless of the sophistication with the conventional suspension system, it would be quite

impractical to work with wheels without pneumatic tires, or several other form involving tire that authorized

considerable bump deviation. The loads fed into the wheels without such auto tires will be enormous from

basically slow speeds, and continual steering wheel failure would get the norm.

A couple of figures will show what I entail: –Assume a bicycle, with a typical size front steering wheel, hits a twenty-five

logistik, sharp edged lump at 190 km/h. This not just a significant bump.

With no car tire the wheel would then be subject matter to an average vertical acceleration associated with approximately

1000 Gary the gadget guy. (the peak price would be greater than this). This method than if typically the wheel and braking mechanism

assembly a new size of 25 kg. then the average point load around the rim would get 245 kN. or about 25

plenty. What wheel could stand that? In case the wheel was initially shod having a standard tire, then this might have at

ground level, a spring price, to a well-defined edge, of approx. 17-35 N/mm. Typically the maximum force and then

transmitted to the wheel for a twenty-five mm. step would be about 425-875 And. i. e. below four thousandths

of the previous figure, which load would end up being more evenly spread around the rim. With out the tire the particular

shock loads passed back to the particular sprung part regarding the bike might be much better too. The straight steering wheel

velocity might be quite definitely higher, and so typically the bump damping makes, which depend about wheel

velocity, might be tremendous. These kinds of high forces would be transmitted directly returning to bike and biker.

The following five charts show some outcomes of a personal computer simulation of accelerations and

displacements upon a typical highway motorcycle, and show the tire’s significance to comfort plus highway

holding. The bike is travelling at 100 km/h. and the front side wheel hits a new 0. 025 metre high step at 0. 1

secs. Note that the time scales vary from graph in order to graph.

Three instances are considered:

� With typical straight tire stiffness in addition to typical suspension cropping and damping.

� With identical wheel properties but along with a suspension spring and coil rate of 100 X those of the particular previous.

� Along with tire stiffness one hundred X the over and with normal delay, pause springing.

So basically we have been considering the typical case, one more case with practically no suspension cropping and

the final case is with a virtually rigid tire. Structural packing, comfort and roadholding would all be adversely

affected with no the initial extra padding of the car tire. Remember that the above charts aren’t just about all to the same time scale,

this is usually in order to better demonstrate the right points.

This specific shows the up and down displacement of typically the front wheel. There is little distinction between the optimum

displacements for the particular two cases using a normal tire, for a compact step the top tire absorbs most of the shock. However ,

in the case of a new very stiff fatigue, the wheel movement is increased by a factor of about 10 times. It is obvious of which the tire

leaves the ground in this case and the landing bounces can be seen after 0. 5 seconds.

These shape show the top to bottom movement of the C of Gary the gadget guy of the motorcycle and rider. Just as Fig 1 its clear that typically the stiff tire

will cause higher bike movements, to the obvious loss of comfort.

Showing different accelerations transported towards the bike plus rider, these figure demonstrate vertical

accelerations with the C regarding G. Both of the stiffer wheel or stiffer suspension cases show identical values of about your five or 6 instances

that of the standard case, nevertheless the form of the a couple of curves is very different. Using the stiff suspension there is certainly small

damping and may see that it takes a few process to stay down. The second bump from around 0. 155 seconds is when the

rear tyre hits the stage, this rear tire response is certainly not shown on the other graphs regarding clarity.

Front tire vertical acceleration to the two cases using a normal tire. The early part is similar for your two cases,

the suspension has little effect below, it truly is tire deflection which is most important for this height of step. As in Fig 5 the particular

lack of postponement, interruption damping allows the particular tire to jump for a couple of cycles prior to settling down.

Because in these shape are with the tyre acceleration, the values of the standard case are overwhelmed by the rigid

tire case, together with a peak worth of close in order to 600 G in comparison with nearly 70 G normally. Again note the effects of typically the landing

bounces right after 0. 5 mere seconds. This high velocity would cause very high structural packing.

As the wheel is really good from removing most of the path shocks, right at typically the point of application, perhaps it

can be worth while in order to consider designing it to absorb much more and eliminate the need for other

delay, pause. Unfortunately we would certainly run into additional problems. We need all seen huge construction

machinery jumping down the highway prove balloon wheels, sometimes this takes so violent that will the

wheels really leave the land. Some sort of pneumatic tire acts just like the air spring, as well as the rubber acts seeing that

a damper whenever it flexes, yet when the tire is made larger the springing result overwhelms the

damping and that we then acquire the uncontrolled moving. So you can find functional restraints to the sum of

cushioning that may be built into the tire for virtually any given application.

Side effects of Tire Stress

Obviously, the springing characteristics mentioned previously mentioned are largely affected by the tire inflation

pressure, but there are some other influences also. Carcass material and design and the properties

and even tread pattern regarding the outer layer of rubber all have an impact on the cropping properties and

the particular area in make contact with with the floor (contact patch). Under in addition to over inflation equally allow the tire to be able to

assume non-optimum cross-sectional shapes, in addition the inflation pressure exerts an affect

over the assortment flexibility of some sort of tire and this is a house of the utmost importance to bike

stability. Manufacturers’ tips should be adhered to be able to.

The influence regarding tire pressure about the vertical tightness of an overpriced tire, when packed on

a level surface. These shape are from genuine measured data. Be aware that the springtime rate is near to

linear over the full-range of loading and varies by 14 kgf/mm. in 1. 9 tavern pressure to 20 kgf/mm. with

a couple of. 9 bar. The particular effective spring price when the tire is loaded against a sharp advantage, such as a brick, will be

considerably lower than this, and it is more non-linear due to the modifying shape of the particular contact area since

the tire “wraps” around the thing.

This spring level acts in sequence using the suspension springs and is also an essential part of the particular overall

suspension technique. An interesting house of rubber is the fact when compressed and released it

does not usually return specifically to it’s unique position, this is usually generally known as hysteresis. This kind of effect is displayed

simply for the one. 9 bar. situation, the curve sketched through the loading phase is simply not followed in the course of the

unloading period. The area in between these two shape represents a reduction of energy which usually results in

car tire heating and likewise acts as a sort of suspension damping. In this particular case the vitality lost

over a single loading and unloading cycle is approximately 10% of the particular total stored energy in the

squeezed tire, and is an important parameter handling tire bounce.

Vertical stiffness of a standard road wheel against a set surface at different pumping pressures. This information is from an

Avon Azaro Sport 2 170/60 ZR17. The upward arrows reveal the compression of the tire along with the 2nd line with all the

downward arrow (shown only at 1 ) 9 bar for clarity) shows typically the behaviour of the particular tire when the particular load is unveiled. The

shaded area between the 2 lines represents some sort of loss of vitality called hysteresis. This provides a source involving suspension

damping in addition to also heats the particular tire. (From info supplied by Avon tires. )

Lateral stiffness of typically the same tire proven in fig. being unfaithful. The vertical load was constant with 355 kgf. along with the wheel was

retained vertical. As predicted the tire is somewhat stiffer along with the higher pumping pressure but manages to lose grip or saturates at the

more affordable lateral load of 460 kgf. when compared to 490 kgf. on the lower pressure. (From data supplied by Avon tires. )

Contact Area

Typically the tire must ultimately give it’s assistance towards the bike coming from a small place of rubber in touch with the

ground, and so “contact patch region = vertical pressure � average contact patch surface pressure”. This

applies in any condition.

The contact plot surface pressure is simply not however, the similar as the pumpiing pressure, as will be

sometimes claimed. These people are related nevertheless there are at least four factors which in turn modify the romantic relationship.

Carcass stiffness, carcass shape, surface plastic depth and soft qualities, and road surface area compliance. In case

we have an incredibly high carcass rigidity then inflation stress may have a reduced influence.

Let’s appear at this found in a bit more detail plus see why:

If a tire was performed just like a great inner tube, of which is from very thin rubber and with little tightness unless

inflated, then an internal air pressure would certainly be the only way to support the bike’s weight. Found in this

case the particular contact patch stress would be comparable to that of the particular internal air stress. For an air flow

pressure of 2 bar and a vertical load involving 1. 0 kN. Then the contact area would end up being 5003 sq mm. If we

at this point increased the atmosphere pressure to point out 3 bar typically the area would drop to 3335 sq . mm.

Let’s right now imagine that all of us substitute a firm steel tubular hoop for our rim and even tire, the area in contact

together with the ground will get quite small. In case we now inflate the hoop with some air pressure, it doesn’t take

much imagination in order to see that, unlike the inner tubing, this internal stress will have a minimal result

on the external section of make contact with. Obviously, a tyre is not very much like the steel hoop, nor the internal tube,

but this particular does show of which the carcass rigidity can reduce the particular contact surface area as calculated simply

from inflation stress alone.

I had two sets of testing. For the first I kept typically the tire inflation strain constant at 2 . 4 bar plus varied the car tire

load between 178 and 1210 D. (allowing for the particular weight of the particular glass and wooden beams). Secondly, I actually

keep a consistent weight of 1210 D. and tried various the inflation stress between 2 . not 5 to 1 bar.

Even with the generous allowance intended for experimental error the particular effects are sharp. The graphs show that

the outcome came out to fit reasonably well to a smooth line, there wasn’t much scatter.

Point (1) upon the curve together with constant inflation pressure, shows how a genuine contact patch strain is

lower (just over half) as compared to the inflation stress, or in various other words the make contact with area is better. This is

due to the rubber surface conformity, thus this is usually crucial at low vertical loads, whereas

carcass stiffness grew to become more important as the particular load rose as shown by points (3) to (6) where the

genuine contact pressure is definitely higher than typically the air pressure, my partner and i. e. reduced area of contact.

Measurement setup. Various dumbbells were placed on the final of some sort of beam, which also loaded the tire via

solid plate of glass. The beam was basically arranged to implement force to typically the tire with a four: 1 leverage. As a result a 25

kgf. weight would load the particular tire with 75 kgf. By looking up on the glass the contact area

was initially determined.

The best plot shows the measured contact spot pressure at various wheel loads regarding a constant pumping pressure

of 3. 4 bar. The lower curves show the contact strain at various inflation pressures for the fixed load involving 1210 N. Typically the

numbers at typically the data points match with the contact area tracings in the earlier sketch. The basic line on every plan

shows the particular case of the make contact with patch pressure being equal to typically the inflation pressure.

The particular carcass stiffness helps to support the machine since the air strain will be

reduced, the particular contact patch stress being considerably better than the pumping pressure. I think while

though the a couple of lines will cross at an air pressure of about 3. 5 bar. (although this did not include analyzed by

measurement), in which point typically the surface rubber compression setting will assume the particular greatest importance.

It is as per the steel hoop example above.

We can easily discover the two independent effects of area compliance and body stiffness and just how the

relative value of these differs with load and inflation pressure.

These tests were just done with 1 particular tire, other types will show different detail outcomes but

the total effects should comply with a similar style.

Area Under Cornering

Does cornering affect tire contact location?

Let’s assume a horizontal surface in addition to lateral acceleration associated with 1G. Under these types of conditions the bike/rider

CoG will always be on a line at 45� to typically the horizontal and driving through the get in touch with patch. There will certainly the

resultant power acting along this kind of line through the contact patch associated with 1. 4 occasions the supported bodyweight.

This force is usually the resultant involving the supported weight and the cornering force, which possess the same

size, in this instance of a 45� lean. The power normal to the surface area is simply that due to the particular

supported weight in addition to does NOT vary with cornering force. The cornering force is reacted simply by the

horizontal frictional force generated simply by the tire/road surface area and this frictional force is “allowed” simply by

virtue involving the normal power.

Therefore, to some first approximation cornering force will NOT affect the tire contact area, and in reality this particular

case can be approximated in order to, if we were just considering the inner tube without having an actual tire.

On the other hand in reality, typically the lateral force can cause some extra tire distortion to take place at the

road/tire interface and depending on the tire characteristics, mentioned previously mentioned, the contact area may well

well alter.

Another aspect to be able to this features study course the tire cross-sectional profile. This Dunlop triangular auto racing

car tire, for example, was designed to put more rubberized on the street when leant above, so without even wheel

distortion the speak to patch area enhanced, simply by advantage of the slim angle.