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Dragsters use a combination of large wide tyres or the rear and small narrow tyres on the front this combination is used for the following reasons: The front wheels: The front wheels are very narrow. This is so a minimum of air resistance or drag affects the dragster with lower drag better acceleration an in turn a better top speed can be achieved all leading to a better pass (race time). Now lets try to understand the concept of air resistance and drag. A basic example is placing your hand out the window with your palm facing forwards as you are driving your car along at about sixty kilometres per hour.
You will feel a strong force of the wind (air resistance) pushing back at your hand. Now turn your hand side or so that your little finger is facing the front and your thumb is facing the rear at the same speed. The force of air resistance exerted on your hand is greatly reduced. This force is similar as to that exerted on the front wheels of the dragster. Now dragsters reach speeds of up to five hundred kilometres per hour, imagine the force needed to hold your hand against the wind if your palm was facing the front. It would be much easier to hold your hand side on.
The same as it would be much easier for the dragsters engine to push the narrow front wheels compared to large ones. Air resistance is a form of friction (namely fluid friction) a friction from the air, as we know friction is defined as a force that opposes movement. The formula used to determine aerodynamic drag is as follows: Drag = 0. 5 rho Cd v 2 S Aerodynamic drag is a function of the following: rho is the air density, which we cannot change. v 2 is velocity squared which is endeavoured to be maximized for the best time and / or pass.
S is the frontal or cross sectional area which we want to minimize. I. e. less frontal area means that a less significant amount of air resistance impedes the top speed and acceleration. Cd is the coefficient of drag, which we want to minimize. So the two things with which can be worked with or changed, the frontal area and coefficient of drag, both of which need to be to minimized for the best results.
Having very narrow front wheels minimizes the frontal area. This is the main reason why narrow front wheels are used. If the smaller the wheel the lower the drag, why not have the wheels narrow and very short as well? You ask. Well the reason is that if the wheels were very small they would drop into all the bumps and cause a loss of speed not to mention control. As the wheels would bounce into the depression and then launch up into the air as they come out of the bump.
This is extremely dangerous in that the driver can no longer steer the vehicle that is travelling at near five hundred kilometres per hour, the car can also get air flowing underneath the car, with the effect of air resistance the car will lift up of the ground and flip through the air. Also the rotational force is much harder on the bearings causing more wear and friction meaning slower times. Large wheels are used because they will skim over the bumps and keep the car moving along a flat plane. They also exert less force on the bearings meaning less friction and better times. Now if drag cars use narrow front wheels so they can get less air resistance and a better top speed why dont all racing vehicles run narrow front wheels? The answer is friction.
The front wheels of drag cars do not have high cornering or driving force travelling trough them. I. e. they are only there to hold the front of the car up and allow it to roll along the road. In conventional racecar's high forces are exerted on the tyre in the horizontal plane meaning that they need to have a good tread area so that they grip the road well and hold the car on the track so it does not slide off into the dirt. A consequence of this is that narrower wheels mean less mass or weight which in turn means less force is required to move the wheel which means more force can go into propelling the car forwards.
The rear wheels: The rear wheels on a dragster are used in an entirely different matter. The rear wheels on a dragster are very wide and very tall when compared to the front wheels. This greatly increases the air resistance, which we saw in the front wheels impedes the performance of the dragster. However this increase in air resistance is greatly outweighed by the gains due to friction. The rear wheels have a large tread width and circumference, which means they have a very large footprint in comparison to the front wheels.
A footprint it tyre terminology is basically the amount of the tyre that comes in contact with the road at one time. In terms of the rear wheels the larger the rear wheels the better. This is because huge amounts of force are put through the rear wheels by the engine to drive the car forwards at the maximum possible acceleration. Stress = Force Surface Area Where: Stress, is the amount of force that can be put through the wheel without breaking the friction force Force is the energy that is put onto the tyre by inertia.
Surface area is the footprint of the tyre. Fr = N Where: Fr = Friction force which we want to maximize = the coefficient of friction is defined as the ratio of tangential force to normal load during a sliding process. N = normal force. i. e. the force that is acting between the road and tyre (gravitational and reaction forces).
The amount of force generated on the wheel by the engine is in the vicinity of 1000 horsepower or nearly 800 kilowatts. Now if the rear wheels were very narrow the amount of force generated could only be applied at a lower rate, because the less stress and coefficient of friction created this means that the wheels would spin on the road more easily, causing the dragster to have poor acceleration and a low top speed meaning a slow time. So the dragsters run a very wide tyre with a large footprint so that a maximum of force can be applied in a minimum amount of time so as not to spin the wheels but obtain maximum acceleration and drive from the line obtaining the best top speed possible and acquiring the fastest time. The force placed though the rear tyres of a dragster under acceleration relates to Newtons third law of motion, in that every force has an equal and opposite reaction. In the case of the dragster the wheel of the dragster pushes backwards on the earth. Since it is improbable for the dragster to rotate the earth, the dragster is propelled forwards by the earth pushing forwards on the wheel opposing its force.
The force exerted onto the earth is such however that the tar on the road will stretch and move to the rear of the dragster with the force of the wheel driving forwards. So how do we obtain the greatest amount of traction (friction) from the rear tyres, as this allows us to put more force onto the tyre and get a better acceleration? The first method is to run very wide and tall tyres to get a larger footprint, as explained previously, however the governing bodies limit the size of the tires to be used. So they run smooth tyres called slicks these tyres have the greatest surface area because they have a flat surface and in turn have the greatest amount of stress and coefficient of friction...
So if we have got the widest and tallest slick tyres possible how can we gain extra traction? The first step is to run very low tyre pressure, around six or sever psi (pounds per square inch) This causes the tyre to squat down and squish onto the road creating a even larger footprint. The next method is to make the rubber sticky so that it will grip the road like glue and prevent the wheels spinning across the road, which reduces acceleration. So how do we get the rubber really sticky? Well two methods are used a chemical change and a physical change are used.
Firstly the chemical change is preformed. A Hydrocarbon, solvent Xylene is painted onto the tread (road touching part of the tyre). This softens the bonds between the rubber and makes it very sticky. The next step is the physical change, which is preformed just before that start of the pass. Where the car does a large burn out which involves putting a large amount of force through the rear wheels to an extent where they spin across the road at high velocity due to the friction force being overcome. This causes the rubber to become extremely hot and sticky due to friction and elastic deformation of the rubber bonds.
When in this sticky state the wheels can withstand a maximum amount of force without spinning the wheels due to and increased coefficient of friction, gaining a up most level of acceleration in turn obtaining a high top speed and attaining a fast time. It is somewhat ironic that the narrow front wheels have been used to reduce friction and the wide rear wheels have been used to obtain the greatest amount of friction. Albeit different types of friction in the front wheels fluid friction from the air is trying to be minimized. In the rear wheels kinetic friction is trying to be maximised so that newtons third law is proven in that the wheel pushing back on the earth will have a reaction of the earth pushing back on the wheel. Racing cars use either slicks or wet weather racing tyres. The properties and differences between each are as follows: Slick tyres: In racing slick tyres are used in dry conditions.
This is because a slick tyre offers the largest footprint. The footprint of a tyre is defined as the surface area of a tyre that comes in contact with the road surface at any one time. Fr = N Where: Fr = Friction force which we want to maximize = the coefficient of friction is defined as the ratio of tangential force to normal load during a sliding process. N = normal force. i.
e. the force that is acting between the road and tyre (gravitational and reaction forces). This only changed by the inertial force pushing onto the outside tyres. (more detail later) In the case of tyres the larger the footprint the greater the surface area and the greater the grip (coefficient of friction between the road and tyre) thus the faster we can go around corners. Now the first way to get a large footprint is to run a slick tyre as previous...
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Research essay sample on Air Resistance Tyres And Friction
