Activity

This could be the first in a number of articles exploring bike tire basics and various basic active characteristics of the handling behavior involving motorcycles. Overall this particular is an extremely complex subject

and wishes a good degree of mathematics plus physics to properly understand what’s happening.

On the other hand, in these articles I’ll try plus explain the basics with the overall minimum of mathematics,

but where this specific is unavoidable I’ll not exceed very simple trigonometry. For people who are unhappy

with any math concepts whatsoever, don’t be concerned, just skip those parts and typically the rest should even so prove useful.

I will try and show the mechanics numerous sketches and graphs.

It seems extraordinary that just 2 small contact areas of rubber, could support our machines and

are able to supply large amounts regarding power to the particular road, whilst in the same time supporting cornering

causes at least around the weight of the bike in addition to rider. Consequently the tires exert probably the single

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

characteristics prior to the other various areas of chassis design.

If Newton first expounded to the entire world his theories associated with mechanics, no doubt he had in the mind,

things apart from the interaction of motorcycle tires with the terrain. Never-the-less the

suppositions are every bit as valid for this kind of situation. Specifically the third law claims, “For every push there

is surely an equivalent and opposite force to resist that. ” as well as to set it another approach “Action and effect are equal and

opposite. ”

Relevant this to tyre action, means of which when the car tire is pushing on the highway then the highway is pushing

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

supporting the involving the bike or perhaps resisting cornering, braking or driving masses.

What this particular law of Newton will not concern on its own with, is which usually force is the particular originating one or

indeed can it subject for many reasons analysis. However, as a guide to typically the understanding of

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

The pushes that occur in between the ground as well as the tires determine a whole lot the behaviour in our

machines, but they will are so often obtained for granted. auto tires really perform these kinds of a large number of different

jobs and the apparent convenience hides the education of engineering style that goes straight into their

design and fabrication. Initially pneumatic tires were built in to improve comfort and reduce loads in

the wheels. Even with modern suspension systems it is still the tires that provide the first distinctive line of

defence for ingesting road shocks.

To explore carcass construction, proceed compound and proceed pattern in great detail is further than the scope

of the book. Rather we have been concerned here with a few basic principles and even their effects in handling

characteristics.

Excess weight Support

The obvious purpose of the exhaust is to support the weight of the particular machine, whether vertical or

leaning more than in a nook. Nevertheless , the genuine mechanism in which the particular air pressure and even tire passes

the wheel load for the road is generally misunderstood. Consider fig. 1, this draw represents a piece

throughout the bottom of a rim and even tire of unit thickness having an inflation pressure of G. The left hand

section shows the tyre unloaded along with the proper hand side shows it supporting the weight F. If

loaded the tyre is compressed top to bottom and the width increases as proven, perhaps surprisingly the

internal air stress does not alter significantly with weight, the interior volume will be little changed.

At the widest part (X1) from the not loaded tire the interior 1 / 2 width is W1, and so the force normal to be able to

it due to the internal stress is simply a couple of. P. W1. This specific force acts in excess towards the wheel

edge, but as the pressure and width of tire are evenly distributed throughout the area the overall

effect is completely balanced. This force in addition has to be opposed by the same pressure (T) in the tyre

carcass.

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

Therefore, the excess force above it, when crammed, is 2. G. (W2 – W1) but since the tyre is only

widened more than a small part of the base area of the circumference, this particular force supports the particular load F.

Typically the above describes how the inflation pressure plus tire width raise produce forces to be able to oppose the

directory wheel loading, yet would not completely explain the detail involving the mechanism by simply which these

causes are transferred in order to the rim. Typically the bead of some sort of fitted tire will be an interference fit over the bead seat of

the wheel rim, which positions this area directly into compression, the in-line element of the side-wall pressure

due to be able to the inflation pressure reduces this compression setting somewhat. This component is shown while F1 on

typically the unloaded half involving F1 = Capital t. cos(U1). The better angle U2 associated with the side-wall any time loaded means

how the in-line component associated with the tension is reduced, thereby also restoring a few of the rim to tire

bead compression. This only happens in the lower part associated with the tire circumference, where the extending

takes place. And so there exists a nett rise in the compressive force on the decrease rim acting upwards, this

supports the bike weight. Typically the nett force will be the difference involving the unloaded plus loaded in-line

makes,

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

The left hand side displays half of an inflated but

not loaded tire, an anxiety (T) is created within the carcass simply by

the interior pressure. To the right, typically the compressed and even

widened shape of typically the loaded tire is shown.

Suspension Activity

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

as the utmost important element in typically the machine’s suspension technique. To the extent that, although

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

additional form of obstruct absorption. In truth rear suspension was basically not by any means standard until the 1940s or 50s.

Whilst, regardless of typically the sophistication in the typical suspension system, it could be quite

impractical to utilize wheels without pneumatic tires, or some other form involving tire that permitted

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

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

A couple of figures will illustrate what I result in: –Assume which a motorcycle, with a typical size front wheel, hits a twenty five

millimeter, sharp edged bump at 190 km/h. This not really a large bump.

Without car tire the wheel would likely then be theme to an average vertical acceleration of approximately

1000 Grams. (the peak worth would be higher than this). This method than if typically the wheel and brake

assembly had a bulk of 25 kg. then the common point load around the rim would be 245 kN. or about 25

loads. What wheel could stand that? If the wheel was shod having a typical tire, then that would certainly have at

ground level, a spring charge, to a razor-sharp edge, of approx. 17-35 N/mm. The maximum force then

transmitted towards the rim for a twenty-five mm. step would be about 425-875 In. i. e. below four thousandths

from the previous figure, and this load would be more evenly distribute round the rim. Without having the tire typically the

shock loads handed back to the particular sprung part of the bike would certainly be much higher too. The vertical wheel

velocity would likely be a lot greater, and so the particular bump damping makes, which depend in wheel

velocity, might be tremendous. These high forces will be transmitted directly returning to bike and rider.

The following several charts show several outcomes of a computer simulation of accelerations and

displacements about a typical road motorcycle, and illustrate the tire’s relevance to comfort and road

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

seconds. Note that typically the time scales differ from graph in order to graph.

Three circumstances are considered:

� With typical up and down tire stiffness and typical suspension cropping and damping.

� With identical car tire properties but along with a suspension originate rate of hundred X regarding typically the previous.

� With tire stiffness hundred X the over sufficient reason for normal delay, pause springing.

So fundamentally were considering the typical case, one more case with nearly no suspension springing and

the ultimate case is along with a virtually rigorous tire. Structural loading, comfort and roadholding would all end up being adversely

affected without having the initial cushioning of the tyre. Be aware that the previously mentioned charts are not almost all to the same amount of time scale,

this is only to better illustrate the proper points.

This kind of shows the up and down displacement of the particular front wheel. Generally there is little variation between the optimum

displacements for the particular two cases along with a normal tire, for a little step the entrance tire absorbs the majority of of the jolt. Yet ,

in the particular case of some sort of very stiff fatigue, the wheel activity is increased by a factor of approximately 10 times. This is obvious of which the tire

leaves the ground in this case along with the landing bounces can be seen after 0. five seconds.

These shape show the straight movement of the particular C of Gary the gadget guy of the bike and rider. As with Fig 1 it really is clear that the stiff tire

causes higher bike actions, to the obvious loss of comfort.

Displaying the several accelerations sent for the bike and even rider, these figure show the vertical

accelerations in the C of G. Both associated with the stiffer tire or stiffer postponement, interruption cases show related values of about a few or 6 times

those of the standard case, however the condition of the two curves is pretty different. With the stiff suspension there is little

damping and that we can see that that takes a few cycles to settle down. The second bump from around 0. 155 seconds is when the

rear tyre hits the stage, this rear steering wheel response is not really shown on the particular other graphs with regard to clarity.

Front steering wheel vertical acceleration for the two cases which has a normal tire. The first part is similar to the two circumstances,

the suspension has got little effect below, it truly is tire deviation this is the most important for this level of step. Such as Fig 5 the

lack of suspension system damping allows the particular tire to bounce for some cycles before settling down.

As in these shape are of the tyre acceleration, the principles of the standard case are overcome by the rigid

tire case, with a peak benefit of close to 600 G as opposed with nearly eighty G normally. Again note the consequences of the particular landing

bounces after 0. 5 just a few seconds. This high speeding would cause quite high structural launching.

As the tyre is indeed good from removing almost all of the highway shocks, right at the particular point of app, perhaps it

would be worth while to consider designing that to absorb more and eliminate the particular need for other

suspension system. Unfortunately we would likely run into additional problems. We have all seen big construction

machinery bouncing down the road on the balloon auto tires, sometimes this gets so violent that the

wheels actually leave the land. A new pneumatic tire acts just like an air spring, and the rubber acts as

a damper any time it flexes, but when the tyre is made larger the springing result overwhelms the

diffusing and that we then obtain the uncontrolled moving. So you will discover practical restraints for the sum of

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

Effects of Tire Pressure

Obviously, the springing characteristics mentioned over are largely impacted by the tire inflation

pressure, but there are various other influences also. Body material and construction as well as the properties

and tread pattern associated with the outer part of rubber just about all have an impact on both springing properties plus

the area in get in touch with with the land (contact patch). Under in addition to over inflation the two allow the tire in order to

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

over the spectrum of ankle flexibility of the tire and this kind of is a home of the utmost importance to motor bike

stability. Manufacturers’ tips should always be adhered in order to.

The influence regarding tire pressure on the subject of the vertical firmness of an filled with air tire, when loaded on

a level surface. These curves are from genuine measured data. Take note that the planting season rate is near

linear over the particular full-range of packing and varies by 14 kgf/mm. at 1. 9 bar pressure to nineteen kgf/mm. at

two. 9 bar. The particular effective spring level when the car tire is loaded towards a sharp advantage, like a brick, is

considerably lower as compared to this, and is even more non-linear as a result of changing shape of the contact area as

the tire “wraps” around the item.

This spring price acts in sequence together with the suspension springs and it is an important part of the particular general

suspension method. An interesting real estate of rubber is that when compressed and released it

does not usually return accurately to it’s unique position, this is definitely known as hysteresis. This effect is demonstrated

simply for the 1. 9 bar. circumstance, the curve sketched throughout the loading phase is not followed throughout the

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

tire heating and also acts as a type of suspension damping. In this particular case the vitality lost

over one loading and unloading cycle is roughly 10% of typically the total stored energy in the

compressed tire, and is an important parameter controlling tire bounce.

Top to bottom stiffness of the standard road tire against a set area at different pumping pressures. This information is from an

Avon Azaro Sport 2 170/60 ZR17. The particular upward arrows suggest the compression associated with the tire along with the 2nd line with the

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

shaded area between the a couple of lines represents some sort of loss of power called hysteresis. This provides a source regarding suspension

damping plus also heats typically the tire. (From info supplied by Avon tires. )

Lateral stiffness of typically the same tire proven in fig. being unfaithful. The vertical weight was constant at 355 kgf. as well as the wheel was

retained vertical. As expected the tire will be somewhat stiffer using the higher pumping pressure but will lose grip or saturates at the

more affordable lateral load regarding 460 kgf. when compared with 490 kgf. at the lower pressure. (From data supplied by Avon tires. )

Contact Area

Typically the tire must ultimately give it’s help for the bike through a small place of rubber talking to the

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

applies in any condition.

The contact patch surface pressure is simply not however, the identical as the inflation pressure, as will be

sometimes claimed. They are related yet there are no less than four factors which usually modify the romantic relationship.

Carcass stiffness, carcass shape, surface plastic depth and real softness, and road surface compliance. If

we have an extremely high carcass stiffness then inflation stress may have a decreased influence.

Let’s look at this inside a bit more detail and even see why:

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

inflated, then an internal air pressure would be the just ways to support typically the bike’s weight. In this

case typically the contact patch strain would be comparable to that of the internal air strain. For an air

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

today increased the air flow pressure to point out 3 bar the area would tumble to 3335 sq . mm.

Let’s now imagine that all of us substitute an inflexible steel tubular hoop for our rim plus tire, the region in contact

using the ground will be quite small. In case we now inflate the hoop which includes air pressure, it shouldn’t take

much imagination to be able to see that, contrary to the inner tubing, this internal pressure will have a negligible effect

on typically the external area of make contact with. Obviously, a wheel is not the same as the steel ring, nor the internal tube,

but this kind of does show of which the carcass solidity can reduce the contact surface area as calculated solely

from inflation stress alone.

I did two sets of tests. For the initial I kept the particular tire inflation stress constant at 2 . not 4 bar and varied the tire

load between a hundred and seventy-eight and 1210 D. (allowing for the weight of typically the glass and wood beams). Secondly, We

keep a constant load of 1210 And. and tried various the inflation strain between installment payments on your some to 1 club.

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

the final results appeared to fit reasonably well to the smooth line, right now there wasn’t much spread.

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

lower (just over half) than the inflation stress, or in various other words the speak to area is greater. This is

because of the rubber surface complying, thus this is usually essential at lower vertical loads, whereas

carcass stiffness started to be essential as the load rose since shown by points (3) to (6) where the

actual contact pressure is usually higher than the air pressure, my partner and i. e. reduced place of contact.

Dimension setup. Various weight loads were placed about the conclusion of the beam, which also loaded the wheel via

thick plate of glass. The beam was initially arranged to apply the burden to typically the tire with a 5: 1 leverage. Thus a 25

kgf. fat would load the tire with one hundred kgf. By tracing above the glass the particular contact area

was basically determined.

The top rated plot shows typically the measured contact plot pressure at several wheel loads regarding a constant pumping pressure

of 2. 4 bar. The lower curves present the contact pressure at various inflation pressures for the fixed load associated with 1210 N. Typically the

numbers at the particular data points overlap with the speak to area tracings in the earlier sketch. The simple line on each plan

shows typically the case from the get in touch with patch pressure being equal to the particular inflation pressure.

Typically the carcass stiffness really helps to support the equipment because the air stress is

reduced, the contact patch strain being considerably larger than the pumping pressure. I think as

though the two lines will mix at an atmosphere pressure of about 3. 5 club. (although this did not include tested by

measurement), from which point the particular surface rubber compression will assume the greatest importance.

This is certainly as per the steel hoop analogy above.

We can easily observe the two independent effects of area compliance and body stiffness and precisely how the

relative importance of these varies with load and/or inflation pressure.

These tests were only done with one particular particular tire, various other types will show different detail results although

the overall effects should adhere to a similar style.

Visit this page Under Cornering

Does cornering have an effect on tire contact region?

Let’s assume some sort of horizontal surface plus lateral acceleration involving 1G. Under these types of conditions the bike/rider

CoG will become over a line with 45� to typically the horizontal and driving through the make contact with patch. There will some sort of

resultant pressure acting along this kind of line through the contact patch associated with 1. 4 times the supported pounds.

This force is usually the resultant involving the supported bodyweight and the cornering force, which include the same

magnitude, in this illustration of a 45� lean. The power normal to the surface area is simply of which due to the particular

supported weight and even does NOT fluctuate with cornering push. The cornering power is reacted simply by the

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

virtue associated with the normal force.

Therefore, to some 1st approximation cornering pressure will NOT affect the tire contact region, and in simple fact this particular

case could be approximated in order to, if we were just considering the particular inner tube with out a real life tire.

However in reality, typically the lateral force will cause some added tire distortion to happen at the

road/tire interface and dependent on the car tire characteristics, mentioned previously mentioned, the contact location might

well modify.

Another aspect in order to this is of training course the tire cross-sectional profile. The old Dunlop triangular race

wheel, for example, was designed to put more rubber on the highway when leant more than, so without even tyre

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