It seems incredible that just two small contact patches of rubber, can support our machines and manage to deliver large amounts of power to the road, whilst at the same time supporting cornering forces at least as much as the weight of the bike and rider.As such the tires exert perhaps the single most important influence over general handling characteristics, so it seems appropriate to study their characteristics before the other various aspects of chassis design.When Newton first expounded to the world his theories of mechanics, no doubt he had on his mind, things other than the interaction of motorcycle tires with the road surface.Never-the-less his suppositions are equally valid for this situation.
This applies equally well regardless of whether we are looking at supporting the weight of the bike or resisting cornering, braking or driving loads.What this particular law of Newton does not concern itself with, is which force is the originating one nor indeed does it matter for many purposes of analysis.However, as a guide to the understanding of some physical systems it is often useful to mentally separate the action from the reaction.The forces that occur between the ground and the tires determine so much the behaviour of our machines, but they are so often taken for granted.tires really perform such a multitude of different tasks and their apparent simplicity hides the degree of engineering sophistication that goes into their design and fabrication.Initially pneumatic tires were fitted to improve comfort and reduce loads on the wheels.Even with modern suspension systems it is still the tires that provide the first line of defence for absorbing road shocks.To explore carcass construction, tread compound and tread pattern in great detail is beyond the scope of this book.Rather we are concerned here with some basic principles and their effects on handling characteristics.
Weight Support The most obvious function of the tire is to support the weight of the machine, whether upright or leaning over in a corner.1, this sketch represents a slice through the bottom of a rim and tire of unit thickness with an inflation pressure of P.The left hand side shows the wheel unloaded and the right hand side shows it supporting the weight F.When loaded the tire is compressed vertically and the width increases as shown, perhaps surprisingly the internal air pressure does not change significantly with load, the internal volume is little changed.This force acts upwards towards the wheel rim, but as the pressure and tire width are evenly distributed around the circumference the overall effect is completely balanced.Therefore, the extra force over this section, when loaded, is 2.The bead of a fitted tire is an interference fit over the bead seat of the wheel rim, which puts this area into compression, the in-line component of the side-wall tension due to the inflation pressure reduces this compression somewhat.This only happens in the lower part of the tire circumference, where the widening takes place.So there is a nett increase in the compressive force on the lower rim acting upward, this supports the bike weight.To the right, the compressed and widened shape of the loaded tire is shown.This reduction is greater with the loaded tire resulting in a greater compressive force on the lower part of the rim.This is the principle but not the only mechanism which passes force from the wheel to the ground, the above ignores the effects of the flexure stiffness of the carcass itself, in addition to supporting the tension forces as outlined, the side-walls also have some bending resistance which can resist small wheel loads without any internal air pressure.To the extent that, whilst uncomfortable, it would be quite feasible to ride a bike around the roads, at reasonable speeds with no other form of bump absorption.In fact rear suspension was not at all common until the 1940s or 50s.Whereas, regardless of the sophistication of the conventional suspension system, it would be quite impractical to use wheels without pneumatic tires, or some other form of tire that allowed considerable bump deflection.The loads fed into the wheels without such tires would be enormous at all but slow speeds, and continual wheel failure would be the norm.With no tire the wheel would then be subject to an average vertical acceleration of approximately 1000 G.This means than if the wheel and brake assembly had a mass of 25 kg.then the average point load on the rim would be 245 kN.The maximum force then transmitted to the wheel for a 25 mm.less than four thousandths of the previous figure, and this load would be more evenly spread around the rim.Without the tire the shock loads passed back to the sprung part of the bike would be much higher too.The vertical wheel velocity would be very much greater, and so the bump damping forces, which depend on wheel velocity, would be tremendous.These high forces would be transmitted directly back to bike and rider.With identical tire properties but with a suspension spring rate of 100 X that of the previous.With tire stiffness 100 X the above and with normal suspension springing.So basically we are considering a typical case, another case with almost no suspension springing and the final case is with a virtually rigid tire.Structural loading, comfort and roadholding would all be adversely affected without the initial cushioning of the tire.Note that the above charts are not all to the same time scale, this is simply to better illustrate the appropriate points.This shows the vertical displacement of the front wheel.There is little difference between the maximum displacements for the two cases with a normal tire, for a small step the front tire absorbs most of the shock.It is obvious that the tire leaves the ground in this case and the landing bounces can be seen after 0.These curves show the vertical movement of the C of G of the bike and rider.As in Fig 1 it is clear that the stiff tire causes much higher bike movements, to the obvious detriment of comfort.Demonstrating the different accelerations transmitted to the bike and rider, these curves show the vertical accelerations at the C of G.Both of the stiffer tire or stiffer suspension cases show similar values of about 5 or 6 times that of the normal case, but the shape of the two curves is quite different.With the stiff suspension there is little damping and we can see that it takes a few cycles to settle down.155 seconds is when the rear wheel hits the step, this rear wheel response is not shown on the other graphs for clarity.Front wheel vertical acceleration for the two cases with a normal tire.The early part is similar for the two cases, the suspension has little effect here, it is tire deflection that is the most important for this height of step.As in Fig 5 the lack of suspension damping allows the tire to bounce for a few cycles before settling down.Again note the effects of the landing bounces after 0.This high acceleration would cause very high structural loading.As the tire is so good at removing most of the road shocks, right at the point of application, perhaps it would be worth while to consider designing it to absorb even more and eliminate the need for other suspension.We have all seen large construction machinery bouncing down the road on their balloon tires, sometimes this gets so violent that the wheels actually leave the ground.A pneumatic tire acts just like an air spring, and the rubber acts as a damper when it flexes, but when the tire is made bigger the springing effect overwhelms the damping and we then get the uncontrolled bouncing.So there are practical restraints to the amount of cushioning that can be built into a tire for any given application.Under and over inflation both allow the tire to assume non-optimum cross-sectional shapes, additionally the inflation pressure exerts an influence over the lateral flexibility of a tire and this is a property of the utmost importance to motorcycle stability.The influence of tire pressure on the vertical stiffness of an inflated tire, when loaded on a flat surface.This spring rate acts in series with the suspension springs and is an important part of the overall suspension system.case, the curve drawn during the loading phase is not followed during the unloading phase.The area between these two curves represents a loss of energy which results in tire heating and also acts as a form of suspension damping.Vertical stiffness of a standard road tire against a flat surface at different inflation pressures.The shaded area between the two lines represents a loss of energy called hysteresis.This acts as a source of suspension damping and also heats the tire.The lateral spring rate is less than half that of the vertical rate at 7.It is interesting to note that at the higher pressure the tire saturates or loses adhesion at the lower figure of 460 kgf.Saturation is indicated when the curve more or less becomes horizontal, this is when the tire cannot support an more lateral force and it displaces or slides sideways, with an approximately constant force.The contact patch area and pressure produced at the lower air pressure has allowed more static grip.However, these tests are done with the artificial case of an upright and non-rotating wheel and hence it would be risky to extrapolate this grip characteristic to a moving machine.Although not shown, the lateral deformation would also be subject to some hysteresis and this damping and the lateral flexibility exert an important influence over the weave stability.As expected the tire is somewhat stiffer with the higher inflation pressure but loses grip or saturates at the lower lateral load of 460 kgf.The contact patch surface pressure is NOT however, the same as the inflation pressure, as is sometimes claimed.They are related but there are at least four factors which modify the relationship.Carcass stiffness, carcass shape, surface rubber depth and softness, and road surface compliance.If we have an extremely high carcass stiffness then inflation pressure will have a reduced influence.In this case the contact patch pressure would be equal to that of the internal air pressure.For an air pressure of 2 bar and a vertical load of 1.If we now increased the air pressure to say 3 bar the area would fall to 3335 sq.Obviously, a tire is not exactly like the steel hoop, nor the inner tube, but this does show that the carcass rigidity can reduce the contact surface area as calculated purely from inflation pressure alone.Now, the actual contact area will be considerably increased and the average contact patch pressure will be reduced.Substitute this mental picture back to a real tire and we see that the tread layer of rubber will give us a greater contact area and lower contact pressure than that of the inflation pressure alone.It is this compliance of the surface rubber that gives us more contact with the road when we increase tire width and diameter, but this must be balanced against the opposing effects of the carcass stiffness.Radial and bias or cross ply tires exhibit quite different characteristics in this regard.The properties of the road surface are also important, a soft surface, mud and sand for example, will obviously give support over a wider area of the tire and so reduce the contact pressure.On a hot day with softened tarmac, even a normal road will deflect significantly enough to affect the contact patch.To get a feeling for the degree of departure of the contact patch pressure from the inflation pressure, consider a completely flat tire, in this case the rubber area will probably be no more than 3 or 4 times, at most, the area when inflated correctly.The following describes some simple measurements that I made to check out the actual relationship between load, inflation pressure and contact area.For the first I kept the tire inflation pressure constant at 2.4 bar and varied the tire load between 178 and 1210 N.Even with a generous allowance for experimental error the effects are clear.Various weights were placed on the end of a beam, which also loaded the tire via a thick plate of glass.Tracings of tire footprint for different loads and pressures.The top plot shows the measured contact patch pressure at various wheel loads for a constant inflation pressure of 2.The lower curves show the contact pressure at various inflation pressures for a fixed load of 1210 N.The numbers at the data points correspond with the contact area tracings in the previous sketch.The plain line on each plot shows the case of the contact patch pressure being equal to the inflation pressure.The carcass stiffness helps to support the machine as the air pressure is reduced, the contact patch pressure being considerably higher than the inflation pressure.It looks as though the two lines will cross at an air pressure of about 3.These tests were only done with one particular tire, other types will show different detail results but the overall effects should follow a similar pattern.There will a resultant force acting along this line through the contact patch of 1.This force is the resultant of the supported weight and the cornering force, which have the same magnitude, in this example of a 45 lean.The force normal to the surface is simply that due to the supported weight and does NOT vary with cornering force.Therefore, to a first approximation cornering force will NOT affect the tire contact area, and in fact this case could be approximated to, if we were just considering the inner tube without a real world tire.Another aspect to this is of course the tire cross-sectional profile.The terrain is vast and varied, and the highways plentiful.The mountains of central and northern Utah are some of my favorite places to ride.The Wasatch mountain range runs north to south covering almost all of the central, northern and eastern sections of Utah.From Salt Lake City there are many small canyon roads that lead out of the city and into the mountains.These allow you to climb from the valley floor of 4500 feet above sea level to 9,000 feet above sea level in as few as 30 miles.The roads wind up and out of the valley and into the mountains in almost all directions.I will describe a few of my favorite places to get away from Salt Lake City for a day ride.Most of these rides are short enough for a good day trip.The 2 rides that go to the Uinta mountains and the Nebo mountain loop are longer and will make for a full day adventure.These are all fun short and in some cases very steep canyon adventures.You can make a loop out of Emigration Canyon road, and East Canyon, and or I-80 if you would like.Big Cottonwood Canyon does loop over the top of the mountain into Park City but you get to travel on 2-3 miles of dirt road right at the top of the canyon.Traveling on dirt roads on a big touring motorcycle is an option, but not one I would really recommend if it can be avoided.Mill Creek Canyon road and Little Cottonwood Canyon are dead ends so once you head up the canyon you can expect to return to the same place after the ride.Getting there you have 2 basic routes, I-80, or highway 189 from Provo, Utah.Take either of these routes with Kamas as the destination.If you choose I-80 go east on I-80 and exit south onto Highway 40, follow this a few miles and exit east onto Highway 248 towards Kamas.If you choose highway 189 from Provo, follow this road into Heber, Utah and turn left onto Highway 40, follow this and exit onto Highway 248 towards Kamas Utah.Once you arrive in Kamas, you have two choices going into the Uintas mountains.The Mirror Lake Highway 150, or the Wolf Creek Pass Highway 35 south of Kamas.The Mirror Lake Highway goes all the way over the top.If you have time you can continue on to Evanston, Wyoming.Once in Evanston you can take I-80 and loop back South into the Salt Lake Valley.This is nice ride and long enough with a lunch stop to turn your ride into an all day adventure.On the other hand if you take Wolf Creek Pass Highway 35, to make a loop out of it you will end up in either Duchesne, or you can turn south on Highway 208 and meet up with Highway 40 to loop back to Heber, Utah.I have not ever taken Highway 208 so I cannot recommend that.I have been over 35 all the way to Highway 40 in Duchesne so if you go this route I know you will be ok.One other road worth mentioning is highway 32 from Francis back to Highway 40.This is a nice little short cut between Highway 40 and Highway 35 which is Wolf Creek Pass.This mountain pass is south of Provo about 30 miles, the way I like to drive this loop is from the south end the road loops north over the top of the range and then drops back down into Utah Valley.To make this loop take I-15 south to Nephi, Utah and exit east onto highway 132 follow this east for a few mile then turn left and head north onto the Nebo Loop road.This road winds steeply up to the ridge top of the Nebo Mountains.Once on this road you can follow it for what seem like miles and miles, all the while feeling like you are on top of the world.Like other mountain passes if you have a fear of heights at a few places along the way you want to make sure you are paying attention because the mountain steeply drops off hundreds of feet on the downhill side road.Spring is a nice time in the mountains, because all the flowers are out and the grasses and trees are bright green with new growth.Summer is a nice time to take a ride in the mountains because it allows you to escape the heat of the valley floors.Fall has a different look and feel to it the grasses are brown and dry, but the trees and leaves are a blaze with bright fall colors, as the trees change colors and the leaves fall off in preparation for the up coming winter.Winter in Utah is not a good time to take a motorcycle tour.The roads are icy, salty, covered in gravel, sand and snow.One other thing to remember about taking your Harley Davidson motorcycle in the high mountains.If you are not prepared with an extra set of warm clothes or leather gear in your saddle bags it can be an extremely long and possibly dangerous ride back home.One day about 100 bikers spent well over and hour at the High Uinta Forest Ranger District Information Center.They had all taken a day ride and got caught in massive rain storm, not being prepare for winter weather made for a serious and cold environment.Most of the people on the ride were forced to just wait out the rain in the tiny Rnger Station.That sums up a few of the nice canyon touring rides around Salt Lake City.It certainly is not all the roads available, It is basically the fun roads south of I-80 in Northern Utah.For more nice day rides in Southern and Central Utah stay tuned or check my web site for more information.He jumped into building a custom chopper full force and is assembling the harley davidson parts and the plan, on his web site MyChopperBlog.Check out the web site to learn about building a chopper or to lend a hand.Online motorcycle information includes various prices at which motorcycle is available, discounts on certain models, sale of used motorcycles, insurance, motorcycle parts, free price quotes, motorcycle dealers, latest models.com, find bargains on motorcycle parts and accessories and other automotive products.Get tax and shipping information, merchant ratings, and professional product reviews at this website.You can also find motorcycle parts, apparel, accessories, over 74,000 aftermarket parts, apparel and accessories.You can also easily find information about motorcycle insurance online – GMAC Insurance and Rider Magazine have partnered to provide insurance for cruising and touring bikes.Lee is well known author who writes for autos for more information visit to www.But history shows that there have always been avid, expert female motorcyclists.Here are five famous female riders who are truly old school.This inspired Linda to form a similar association of female motorcyclists.She teamed up with Dot Robinson, a well-known competition rider, to form a club called the Motor Maids.It took Linda and Dot several years to find the 50 members they needed to earn an AMA charter, but the Motor Maids were soon known for their smart uniforms, complete with white gloves.When Dot s mother went into labor with her, Goulding took her to the hospital in a sidecar.As an adult, Dot and her husband were Harley-Davidson dealers in Detroit.When she won a Jack Pine enduro in the sidecar class, she became the first woman ever to win an AMA national competition.She rode until she was well into her 80s, often in a pink riding suit that she adopted in the 1950s, when the customary black leather outfits became associated with outlaw gangs.Despite her early fascination with bikes and her obvious skill as a rider, she was never encouraged to pursue such an unladylike sport.Undeterred, she studied engineering and later took her friend Florence on an epic sidecar journey across the Sahara and south all the way to Cape Town, South Africa.They rebuilt their engine in mid-journey and once pushed their rig 25 miles.They told the whole story in a popular book titled, The Rugged Road.Linda later became the first woman to earn a coveted Gold Star for lapping the Brooklands race oval at over 100 miles an hour.In WWII she became the first woman ever to serve as a British military dispatch rider.where she worked as a motorcycle mechanic, eventually owning her own dealership.She wrote a popular motorcycle training manual, then moved to Phoenix where she operated a riding school.She helped found WIMA, the Women s International Motorcycle Association.She never owned a car and rode until her eyesight failed at the age of 88.She died less than two years after giving up her beloved sport.As an African-American woman in the 30s and 40s, Bessie made several well-publicized cross-country rides, fearlessly taking on both racists and sexists.She was frequently denied accommodation and there are pictures of her sleeping right on her motorcycle.She once disguised herself as a man to win a dirt track race.She said she d owned 27 Harley-Davidsons and one Indian.In 1939, the ISDT was held in Nazi-controlled Austria in the last few days before England declared war on Germany.That year, Britain sent both a civilian and a military team to compete.After four days, when it seemed that war could break out at any minute, British officials told the civilian team to return to England immediately.Cottle refused to leave and competed on the fifth day alongside the British Army team.When they too were ordered to abandon competition, Cottle and the Army team rode their motorcycles to neutral territory in Switzerland.Choosing a driving instructor that is compatible with you is the best way to ensure that you are adequately prepared for your driving test and ultimately more likely to be a better, safer driver, when it is time to go it alone.A good driving instructor will be patient, understanding and approachable.Those factors, along with others should be central to choosing which one is right for you.Referrals When people are happy with a product or service they are usually happy to refer the business to their friends and family.Although your friend or family member may like the driving instructor on a personal level, it is important that you find out if they are also satisfied with his or her teaching ability and how they have turned out as a driver through using their services.Car They Drive Although you may not be too concerned with the kind of car your instructor has, this could become a factor when you eventually get in a car on your own.If, for example, you have bought a large car in preparation for when you pass your test, then you may find it a shock to your system when you have to drive a car that is much larger in size.In that instance, an influencing factor in choosing an instructor could be to choose one that has a car around the same size and engine displacement as the one that you have bought.It is also worthy of note that many driving instructors are happy to take you out in your own car, however it is better to check with them first as not all instructors and schools will be happy to do this.Experience Choosing a more experienced driving instructor will mean that you are more likely to be dealing with someone who knows a lot more than what they had to in order to pass a test.With experience comes knowledge and expertise in how to deal with students, as well as how to act on the road.Although you should not be completely put off working with a younger driving instructor altogether, it is probably best to consider someone with more years of experience to have an advantage where this is concerned.Compatibility One of the most overlooked parts of choosing any service provider is their compatibility with you.Although it may be hard to work this out on a phone, or in a quick meeting, you should try to get a grasp for whether or not you are likely to get on with them.Keep in mind that you do not have to become best friends with your driving instructor, however having a mutual understanding is vital.info The author writes articles about Driving schools or driving instructors and driving schools directory.. 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