Tire balance, also called tire unbalance or tire imbalance, describes the distribution of mass within an automobile tire or the entire wheel (including the rim) on which it is mounted.
When the wheel rotates, asymmetries in its mass distribution may cause it to apply periodic forces and torques to the axle, which can cause ride disturbances, usually as vertical and lateral vibrations, and this may also cause the steering wheel to oscillate. The frequency and magnitude of this ride disturbance usually increases with speed, and vehicle suspensions may become excited when the rotating frequency of the wheel equals the resonant frequency of the suspension.
Tire balance is measured in factories and repair shops by two methods: with static balancers and with dynamic balancers. Tires with large unbalances are downgraded or rejected. When tires are fitted to wheels at the point of sale, they are measured again on a balancing machine, and correction weights are applied to counteract their combined unbalance. Tires may be rebalanced if driver perceives excessive vibration. Tire balancing is distinct from wheel alignment.
Static balance requires the wheel center of mass to be located on its axis of rotation, usually at the center of the axle on which it is mounted. Static balance can be measured by a static balancing machine where the tire is placed on a vertical, non-rotating spindle. If the center of mass of the tire is not located on this vertical axis, then gravity will cause the axis to deflect. The amount of deflection indicates the magnitude of the unbalance, and the orientation of the deflection indicates the angular location of the unbalance. In tire manufacturing factories, static balancers use sensors mounted to the spindle assembly. In tire retail shops, static balancers are usually non-rotating bubble balancers, where the magnitude and angle of the unbalance is indicated by the center bubble in an oil-filled glass sighting gauge. While some very small shops that lack specialized machines still do this process, they have been largely replaced in larger shops with machines.
Dynamic balance requires that a principal axis of the tire's moment of inertia be aligned with the axis about which the tire rotates, usually the axle on which it is mounted. In the tire factory, the tire and wheel are mounted on a balancing machine test wheel, the assembly is rotated at 100 RPM (10 to 15 mph with recent high sensitivity sensors) or higher, 300 RPM (55 to 60 mph with typical low sensitivity sensors), and forces of unbalance are measured by sensors. These forces are resolved into static and couple values for the inner and outer planes of the wheel, and compared to the unbalance tolerance (the maximum allowable manufacturing limits). If the tire is not checked, it has the potential to cause vibration in the suspension of the vehicle on which it is mounted. In tire retail shops, tire/wheel assemblies are checked on a spin-balancer, which determines the amount and angle of unbalance. Balance weights are then fitted to the outer and inner flanges of the wheel.
Although dynamic balance is theoretically better than static balance, because both dynamic and static imbalances can be measured and corrected, its effectiveness is disputed because of the flexible nature of the rubber. A tire in a free spinning machine may not experience the same centrifugal distortion, heat distortion, nor weight and camber that it would on a vehicle. Dynamic balancing may therefore create new unintended imbalances.
Dynamic balancing has traditionally required removing the wheel from the vehicle, but sensors installed in modern cars, such as for anti-lock brakes, could enable estimating the imbalance while driving.
To a first approximation, which neglects deformations due to its elasticity, the wheel is a rigid rotor that is constrained to rotate about its axle. If a principal axis of the wheel's moment of inertia is not aligned with the axle, due to an asymmetric mass distribution, then an external torque, perpendicular to the axle, is necessary to force the wheel to rotate about the axle. This additional torque must be provided by the axle and its orientation rotates continuously with the wheel. The reaction to this torque, by Newton's Third Law is applied to the axle, which transfers it to the suspension and can cause it to vibrate. Automotive technicians can reduce this vibration to an acceptable level when balancing the wheel by adding small masses to the inner and outer wheel rims that bring the principal axis into alignment with the axle.
Vibration in automobiles may occur for many reasons, such as wheel unbalance, imperfect tire or wheel shape, brake pulsation, and worn or loose driveline, suspension, or steering components. Foreign material, such as road tar, stones, ice, or snow, that is stuck in a tire's tread or otherwise adhered to the tire or wheel may also cause a temporary unbalance and subsequent vibration.
Every year, millions of small weights are attached to wheels by automotive technicians balancing them. Traditionally, these weights have been made of lead; it is estimated that up to 500,000 pounds (230 t) of lead, having fallen off car wheels, ended up in the environment. According to the US Environmental Protection Agency, worldwide these total more than 20,000 tonnes of lead annually, and therefore the use of less-toxic materials is encouraged. In Europe, lead weights have been banned since 2005; in the US, some states have also banned them. Alternatives are weights made of lead alloys that include zinc or copper, or weights that are altogether lead-free. In addition, internal tire balancing products are a feasible alternative to tire balancing. They are products which are inserted into the tire when it is mounted to the rim, thus, eliminating the use of hammer-on weights or tape weights.[ citation needed ]
An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle is supported. In the latter case, a bearing or bushing sits inside a central hole in the wheel to allow the wheel or gear to rotate around the axle. Sometimes, especially on bicycles, the latter type of axle is referred to as a spindle.
For motorized vehicles, such as automobiles, aircraft, and watercraft, vehicle dynamics is the study of vehicle motion, e.g., how a vehicle's forward movement changes in response to driver inputs, propulsion system outputs, ambient conditions, air/surface/water conditions, etc.
The unsprung mass of a vehicle is the mass of the suspension, wheels or tracks, and other components directly connected to them. This contrasts with the sprung mass supported by the suspension, which includes the body and other components within or attached to it. Components of the unsprung mass include the wheel axles, wheel bearings, wheel hubs, tires, and a portion of the weight of driveshafts, springs, shock absorbers, and suspension links. Brakes that are mounted inboard are part of a vehicle's sprung mass.
Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.
Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.
In automotive design, a front-engine, front-wheel-drive (FWD) layout, or FF layout, places both the internal combustion engine and driven roadwheels at the front of the vehicle.
In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles, the wheelbase is the distance between the steering (front) axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles.
The wheel size for a motor vehicle or similar wheel has a number of parameters.
A tilting three-wheeler, tilting trike, leaning trike, or even just tilter, is a three-wheeled vehicle and usually a narrow-track vehicle whose body and or wheels tilt in the direction of a turn. Such vehicles can corner without rolling over despite having a narrow axle track because they can balance some or all of the roll moment caused by centripetal acceleration with an opposite roll moment caused by gravity, as bicycles and motorcycles do. This also reduces the lateral acceleration experienced by the rider, which some find more comfortable than the alternative. The narrow profile can result in reduced aerodynamic drag and increased fuel efficiency. These types of vehicles have also been described as "man-wide vehicles" (MWV).
Engine balance refers to how the forces are balanced within an internal combustion engine or steam engine. The most commonly used terms are primary balance and secondary balance. First-order balance and second-order balance are also used. Unbalanced forces within the engine can lead to vibrations.
Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel-drive vehicles. For example, during heavy acceleration, the steering may pull to one side, which may be disturbing to the driver. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. Torque steer is directly related to differences in the forces in the contact patches of the left and right drive wheels. The effect becomes more evident when high torques are applied to the drive wheels because of a high overall reduction ratio between the engine and wheels, high engine torque, or some combination of the two. Torque steer is distinct from steering kickback.
A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have also been used as front axles in four-wheel-drive vehicles. In most automobiles, beam axles have been replaced with front and rear independent suspensions.
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.
A balancing machine is a measuring tool used for balancing rotating machine parts such as rotors for electric motors, fans, turbines, disc brakes, disc drives, propellers and pumps. The machine usually consists of two rigid pedestals, with suspension and bearings on top supporting a mounting platform. The unit under test is bolted to the platform and is rotated either with a belt-, air-, or end-drive. As the part is rotated, the vibration in the suspension is detected with sensors and that information is used to determine the amount of unbalance in the part. Along with phase information, the machine can determine how much and where to add or remove weights to balance the part.
A Bundorf analysis is a measure of the characteristics of a vehicle that govern its understeer balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.
Tire uniformity refers to the dynamic mechanical properties of pneumatic tires as strictly defined by a set of measurement standards and test conditions accepted by global tire and car makers.
The balancing of rotating bodies is important to avoid vibration. In heavy industrial machines such as gas turbines and electric generators, vibration can cause catastrophic failure, as well as noise and discomfort. In the case of a narrow wheel, balancing simply involves moving the center of gravity to the centre of rotation. For a system to be in complete balance both force and couple polygons should be close in order to prevent the effect of centrifugal force. It is important to design the machine parts wisely so that the unbalance is reduced up to the minimum possible level or eliminated completely.
Rotating unbalance is the uneven distribution of mass around an axis of rotation. A rotating mass, or rotor, is said to be out of balance when its center of mass is out of alignment with the center of rotation. Unbalance causes a moment which gives the rotor a wobbling movement characteristic of vibration of rotating structures.
Crosswind stabilization (CWS) is a relatively new advanced driver-assistance system in cars and trucks that was first featured in a 2009 Mercedes-Benz S-Class. CWS assists drivers in controlling a vehicle during strong wind conditions such as driving over a bridge or when overtaking a semi-truck. CWS uses yaw rate, lateral acceleration, steering angle, and velocity sensors to determine how much assistance to give the driver in a certain scenario whether it be at different speeds or while turning. Using different components throughout the vehicle like brakes, differentials, and suspension, CWS can implement the readings from force sensors to properly assist the driver in a given situation.
This glossary of automotive terms is a list of definitions of terms and concepts related to automobiles, including their parts, operation, and manufacture, as well as automotive engineering, auto repair, and the automotive industry in general. For more specific terminology regarding the design and classification of various automobile styles, see Glossary of automotive design; for terms related to transportation by road, see Glossary of road transport terms; for competitive auto racing, see Glossary of motorsport terms.
You may end up with ice and snow packed in your wheels. This solid clump of ice causes a steering-wheel shake because the added mass rotating with the wheel throws off the wheel balance.