An Introduction to Wheel Bearing & Wheel hub Types, Characteristics, And Calcs

An Introduction to Wheel Bearing & Wheel hub Types, Characteristics, And Calcs

1- Introduction
A wheel bearing is the bearing element inside the wheel end that supports radial and axial loads while allowing the wheel to rotate with minimal friction.
Wheel bearings guide and support shafts and axles. They are part of the chassis, guide the wheels and absorb axial and radial forces. Radial forces are longitudinal forces produced as a result of rotation. They are applied to the wheel bearing at a right angle to the longitudinal axis. Axial forces, on the other hand, are forces that act on the wheel bearing in the direction of the longitudinal axis. They are produced during cornering, for example. The axial forces produced during cornering expose wheel bearings to particular stress

Historically, wheel bearings could be serviceable (separate inner and outer bearings or cup-and-cone/tapered roller designs that can be disassembled, cleaned, re­greased and reassembled) or sealed (prepacked bearings pressed into place). The bearing itself consists of inner and outer races plus rolling elements (balls or rollers) and a lubricant/seal system.

A hub bearing (often called a wheel hub assembly, hub unit, or hub and bearing assembly) is a preassembled, factory-sealed unit that integrates the bearing(s) with the hub flange (the part the wheel bolts to). Many hub units also include the wheel speed/ABS tone ring and the wheel speed sensor or provisions for it.
These assemblies are typically greased for life at the factory and are replaced as a single unit when they fail — you don't disassemble them for re-greasing.
Short takeaway: wheel bearings are the bearing elements; hub bearings (hub assemblies) are the ready-to-install units that include bearings plus the hub flange and often sensors and seals.

2- Important Characteristics of Wheel Bearings

• High Durability: Wheel bearing is manufactured of hardened steel or similar materials to resist heavy    pressure and wear and tear.
• Low Friction: Such a bearing lessens friction between different mobile parts for seamless wheel rotation.
• Sealed Construction: Many modern bearings are sealed which means they keep the dirt, moisture, and debris out of the vehicle but lock the bearing's grease.
• Handle Load Perfectly: It not only tolerate heavy radial loads but also thrust loads for best                    performance under changing driving situations

 

3- Wheel bearing& Wheel hub types

Wheel bearings make sure your vehicle stays steady and stable during the drive and its weight is perfectly balanced. The automotive industry relies on the wheel bearings more than you imagine. The types of wheel bearings are:

3-1 Wheel bearings

3-1-1. Ball Bearings

It is the most common type of wheel bearing and is very versatile. Their design allows both radial (side) and thrust (axial) loads. These bearings are very useful in smaller vehicles as they are simple and effective in different environments.

Fig 1

Important Characteristics
• They can handle high speeds
• These can tolerate radial and thrust loads
• They are used primarily in light motor vehicle

3-1-2 Tapered Roller Bearings

Tapered roller bearings bear heavy radial and axial loads like ball bearings. Their cone-like shape provides an even distribution of weight. They are very suitable for vehicles with high stresses, like trucks, SUVs, performance cars, and others.

Fig 2

• They have the ideal load-handling capability
• These are primarily found in the front and back wheel hubs
• It provides durability and strength for heavy us

3-1-3. Roller Bearings (Cylindrical)

Cylindrical ones are less frequent than ball or tapered roller bearings. However, some wheel assemblies use cylindrical roller bearings for heavy- duty uses. These handle radial loads but not very good with axial loads

Fig 3

• They have strong radial load capacity
• These have limited application in automotive wheel hubs

3-1-4. Double Row Bearings

They have two rows of rolling elements

Fig 4

• balls
• or tapered rollers

They give more stability and load-carrying capability. You can use them in higher-performance and reliability vehicles.
Key Features:
• They have increased load support and stability.
• Typical for high-performance or heavy-duty vehicles

3-2 Hub Bearings

Hub bearings, also known as wheel hub units or hub assemblies, are pre-assembled, sealed modules that integrate the bearing, hub flange, mounting bolts, and often an ABS speed sensor ring. They are not serviceable—when worn, the entire unit is replaced. Flub units have evolved through three generations, each offering increased integration and reduced assembly complexity:

• These bearings have integrated designs for additional durability
• They are sealed to minimize contamination
• Reduces the requirement of regular upkeep

Fig 5

3-2-1 Gen 1: Basic bearing with a flange on the outer ring; requires a separate hub and a press fit into the steering knuckle. Still used in some heavy trucks and trailers.

Fig 6

3-2-2 Gen 2: Includes a flange for mounting the wheel and a flange for attaching to the steering knuckle. The outer ring has two bolt holes or studs for direct bolting to the knuckle. Common on many compact and mid-size cars.

Fig 7

3-2-3   Gen 3: Integrates two flanges (wheel side and vehicle side) plus a pre-assembled bearing with optimized internal geometry for reduced weight and improved stiffness. The inner ring includes a flange with wheel studs, and the outer ring has bolt holes for knuckle attachment. Nearly universal on modern front-wheel-drive and all-wheel-drive passenger cars.

Fig 8

3-2-4 The fourth generation currently lacks a unified definition and technical consensus in the industry. Each manufacturer is independently developing and testing according to its own technical roadmap, and it is in the product introduction phase, not yet achieving large-scale application. Currently, the R&D of fourth-generation wheel bearing units in the industry mainly revolves around technological upgrades of third-generation products: on the one hand, further integrating core chassis components such as universal joints and brake discs to achieve one-stop supply of wheel-end components; on the other hand, deepening mechatronics integration, optimizing sensor integration systems, and enriching product functional attributes.

Fig 9

4- Maintenance Guiding and service

wheel bearing need to be replaced

4-1 Signs of Bad Wheel Bearings

Your vehicle's performance and safety do depend on wheel bearings. So, it's important to identify damage signs early, such as:

Fig 10

1-A failing wheel bearing often makes unusual noises that can warn of impending problems. You will probably notice a grinding or growling noise. It happens from metal-on-metal contact due to a lack of lubrication. This noise usually will get louder with speed.

2-If the wheel bearings are loose, they may cause wobbling and vibrations in the wheel assembly. You'll notice this vibration coming from the steering wheel that gets intense with higher speed.

3-ABS is available in most modern cars. There are sensors near the wheel bearings. A failing bearing can interrupt these sensors and can turn on the ABS warning light on your dashboard.

4-Damaged wheel bearings can cause uneven pressure on the tires leading to irregular or rapid wear. This is because the wheel will not rotate as smoothly or evenly as it should.

5-A faulty wheel bearing increases rolling resistance within the wheel assembly and creates friction that can affect the vehicle's general performance. This forces the engine to work harder, as it has to use more energy to move. Therefore, it reduces fuel efficiency. Besides, you may feel your car slow or less responsive. It makes it difficult for any driver to regulate speed effortlessly.

6-It is also a sign of bad bearing if during cornering or applying brake your vehicle starts pulling to one side. This is because the affected wheel would have uneven friction or resistance.

7-If the bearing is bad, it generates too much heat. You can even feel this heat around the wheel area. In extreme cases, you might see smoke coming from the wheel area.

4-2 What can cause a wheel bearing to go bad? Sometimes the wheel bearing deteriorates as a result of normal wear and tear. Moisture and corrosion can cause a wheel bearing to fail prematurely. Pot holes can damage wheel bearings too. We often see wheel bearings getting noisy after an accident or after hitting the curb.

If you suspect a bad wheel bearing, have your car checked. A humming noise when driving can be caused by a number of other problems, including a bad transmission bearing, unevenly worn or "cupped" tires and a worn-out differential.

Since the wheel bearing noise travels through the chassis and body of the vehicle, it's often difficult to pinpoint which bearing is noisy. In most cases,

a mechanic can determine if a wheel bearing is bad by listening for the noise with a mechanic's stethoscope and checking for looseness.

Fig 11

4-3 Is it safe to drive with a bad wheel bearing? It depends on the condition of the bearing. Only your mechanic can determine this during an inspection.

4-4 Do you have to replace both wheel bearings if one is bad? No, it's not necessary. If only one wheel bearing is bad, only that bearing needs to be replaced. There is no need to replace a good wheel bearing as a precaution.
Can a wheel bearing be greased? Only tapered roller wheel bearings can be greased. A double row ball bearing found in most cars is sealed for life and can only be replaced if bad.

4-5 What is the average life of a wheel bearing? in many cars wheel bearings can last the lifetime of a vehicle. In our experience, a vehicle might need one wheel bearing replaced within 150,000 miles. To make the wheel bearings last longer, watch out for potholes and drive slower over speed bumps.

5- Components Related To A bearing Assembly

Race – This is a metal ring with smooth, machined inner and outer surfaces. Bearings are surrounded by a race which provides the outer surface against which they rotate. Races are often included with a new bearing assembly, but check to make sure you know what you’re getting before making a purchase. If a new race is not included with bearings, it should be purchased separately and replaced as well, because an old race should never be re-used – no matter good its condition may appear to the naked eye.

Fig 12

Bearing cage – A special form of race specially perforated to cradle the bearings themselves. The bearing cage provides the inner surface against which bearings rotate. Bearing cages are not usually sold separately because they are typically part of a bearing assembly.

Bearing seal – An O-shaped round seal (usually hardened rubber) used to surround part of a bearing assembly so grease doesn’t leak out. Bearing seals are a wear item, and must always be replaced with bearings. If the bearing assembly for your vehicle does not come with a built-in seal, bearing seals are usually sold individually.

Wheel hub – A forged or cast piece of metal that an automobile wheel mounts to. Wheel bearing assemblies typically fit inside the center of the wheel hub to allow free rotation around an axle shaft or spindle. Bearing assemblies that mount inside a wheel hub are often called wheel hub bearing assemblies. Depending on vehicle manufacturer, some wheel hub bearing assemblies are constructed with integral bearing assemblies which cannot be replaced separately. Instead, the wheel hub must be replaced as a whole.

Bearing grease – This is a heavy-duty petroleum-based or synthetic grease designed to provide lubrication of high-friction surfaces. Unlike gear oil or motor oil, bearing grease remains thick and sticky at high temperatures because of its heavy viscosity, and will not run off surfaces the way thinner fluids do. Having clean grease on hand is essential when doing any repair work involving bearings or related parts. Grease in a container that’s been left open to the air for a period of time tends to draw airborne dust and dirt like a magnet, so if you find the lid of your container was not on tight or has become compromised, your grease has too. Replace it with a new container.

6- car wheel bearing disassembly and reassembly

· Remove the wheel cap and remove the wheel.
· Remove the brake caliper.
· Carefully hang the caliper out of the working area.
· If it is hard to remove, screw a bolt into the exposed threaded hole on the disc to remove it.

Fig 13

· Now the drive shaft lock nut needs to be removed.
· Unstake the staked part of the lock nut by using a screwdriver or similar tool.
· Loosen the drive shaft nut and remove
· Loosely fit the nut until it is flush with the end of the drive shaft

Fig 14

·    Remove the speed sensor
· To remove stearing-arm ball joint, first take out the split pin
· Loosen the ball joint nut

Fig 15

· The ball joint at the stearing-arm end is often secured to the knuckle very tightly
· Use a dedicated tool and hammer it from above with care not to damage the bolt threads
· Loosen and remove the bolts which fasten the knuckle to the suspension. The knuckle can now be          removed.

Fig 16

Removing the wheel bearing from the knuckle

· Insert a crowbar or something similar into the gap to avoid deforming the dust cover when removing       the front axle hub.
· Keep the knuckle horizontal on a support, put a suitable tool on the end face of the hub and remove         the   hub.
· Remove the snap ring from the knuckle
· Remove the dust cover.
· The inner ring must now be removed from the hub. Insert a separator into the gap between the end           face of the inner ring and the hub.
· Pull off the inner ring.
· Alternatively it is possible to use a hydraulic press.

 

Fig 17

· Ensure the knuckle is supported safely and the bearing is in a vertical orientation.
· Reinsert the removed inner ring
· Ensure the dedicated tool outside diameter matches the bearing inner ring.
· Press the bearing out of the knuckle
· Always inspect the knuckle bore and the hub shaft for damage
· Clean the removed parts with a parts cleaner

Installing the new wheel bearing into the knuckle

Tip: Only remove the bearing from its protective packaging immediately before the fitting.

· This is to avoid ingress of dirt and therefore premature bearing failure.
· Use a suitable tool that comes in contact with only the end face of the outer ring.

Fig 18

Tip: Outer diameter of tool < outer diameter of bearing

· It is important to keep the bearing aligned to the knuckle bore and press it vertically into the knuckle.

Fig 19

· Make sure that the bearing is not inclined, and press it until correctly seated.
· Insert a new snap ring.
· Fix the dust cover to the knuckle.
· Support the hub, so that the shaft is vertical
· By using a suitable tool, push on the end face of the inner ring
· Press the bearing until seated against the indicated position.
· Reassembly is the reverse of the dismounting process.
· Reattaching the knuckle to the lower suspension arm and strut
· Attach the speed sensor.
· Attach the ball joint at the tie-rod end.
· Tighten the nut to the specified torque value.

Fig 20

· Insert the split pin. Be sure to use a new one.
· After fitting the new nut by hand, tighten further with a socket to ensure the drive shaft is seated.
· The final torque setting will be done later when the car is on the ground.
· Mount the brake disc and the brake caliper.
· Mount the tyre and lower the car.
· Now the car is on the ground, the drive shaft nut can be tightened to the value specified by the                 manufacturer.
· Stake the nut into the groove of the shaft.

Tip:

· Depending whether the wheel is alloy or steel, there are various torque values and procedures. Please      check carefully with the manufacturer`s instructions.
· Before driving, press several times on the brake pedal to ensure the brake pads come in contact with      the brake discs.
· As the suspension has been disassembled, it is advisable to have the steering geometry checked.

7- Calculation of bearings 

Car wheel bearing load calculations combine static gravity forces from the vehicle weight with dynamic radial and axial {cornering/braking) forces. 

The total load is converted into an equivalent dynamic load

to determine bearing fatigue life (L10)
Static and Dynamic Force Components

• Radial Load (Fr): Derived from the static corner weight of the vehicle plus dynamic bumps. Multiply the static wheel load by a shock factor (1.2 to 2.0) for rough roads

• Axial (Thrust) Load (Fa): Generated during vehicle cornering, lane changes, and camber forces acting sideways on the tire patch

• Offset Distance (δX): The distance from the tire centeriine/load application point to the bearing center, which creates a moment load on double-row or paired single-row bearings

Fig 21

Equivalent Dynamic Load Calculation

When a wheei bearing experiences both radial (Fr) and axial (Fa) loads simultaneously, use the Bearing Load Calculation Guide formula to find the equivalent load (P):

Eq 1

· P is the equivalent radial load.
· (Fr) is the actual radial load.
· (Fa) is the actual axial (thrust) load.
· X is the radial load factor.
· Y is the axial load factor.
· V is the rotation factor (1 for inner ring rotation, 1.2 for outer ring rotation)

X = Radial load factor

How to Find X

· Pure Radial Load (Fa / Fr ≤ e): The radial load factor X is typically set to 1
· Combined Load (Fa / Fr > e): When the axial load exceeds a specific threshold limit (e), 

X takes a constant reduced value (commonly 0.56 for standard deep groove ball bearings), while the axial load factor Y handles the extra thrust influence

· Cylindrical Roller Bearings: Straight roller bearings handle minimal axial load, meaning X = 1.0 and       Y = 0


• Y = Axial load factor (dependent on the contact angle of tapered or angular contact bearings)
• If the axial-to-radia! ratio (Fa/Fr) is below a threshold limit (e), the axial load is negligible, and P = Fr

V is the rotation factor (1 for inner ring rotation, 1.2 for outer ring rotation)

Fig 22

Bearing Life Expectancy (L10)
To calculate nominal fatigue life in millions of revolutions:

Eq 2

• C = Basic dynamic Load rating from the manufacturer
• P = Equivalent dynamic load
• Ƥ- Life exponent (p = 3 for ball bearings, p = 10/3 for roller/tapered bearings)

7-1 SKF Racing - Calculation of Wheel Bearings Loads

Factors necessary for bearing load calculation in wheel applications vary considerably. To obtain an exact expression for the resultant bearing loads is consequently impossible. Values based on experience with previous bearing arrangements are usually used for new designs

Fig 23

The calculation for front and rear hub bearing arrangements are normally similar; no consideration is taken of the fact that one pair of wheels is driven. Only in special circumstances is account taken of the power transmitted

The following survey is based on a hub bearing arrangement, incorporating two taper roller bearings as shown in Fig. 24, but the method of calculation also applies to other bearing arrangements having two pressure centres, for example, using two single row angular contact ball bearings or one double row.

Fig 24

The static hub load K for a loaded vehicle is obtained from

Eq 3

where 

K′ : is the force between tyre and road (half axle load)
K″:  is the weight of one wheel

When rough operating conditions have to be considered, the static load K is increased by 20 per cent.

The effect of the camber angle (in Fig. 24, the angle of the line I- II with the horizontal plane) may usually be ignored, as well as the influence of the driving and rolling resistance forces, which are small compared to the vertical forced caused by gravity. Flowever, where the camber angle is considerable the axial component of the static load K must be taken into account.

In addition to the static load it is necessary to consider other loads, both radial and axial, which are due, for instance, to road surface irregularities. The resultant bearing loads obviously depend on wheel diameter and the distance between the bearings and are taken into account by an additional force fK.

On a straight route the following radial bearing loads should thus be considered, the axial loads ignored.

Eq 4

Indexes I and II denote the inner and outer bearing respectively and with reference to Fig. 24, ε1 = a / l and ε 2 = RH / l . In the 4 equation the plus

sign applies when ε1 < 1 and the minus sign when ε1 > 1 . The value recommended for the coefficient f is 0.05 for private cars and commercial vehicles

Fig 25

When cornering a centrifugal force Kd kg acts at the centre of gravity of the vehicle; see Fig. 25. Its magnitude is obtained from

Eq 5

where: 

G is the maximum weight of the vehicle less the weight of the wheel, kg
v is the speed of the vehicle in km/h
r is the radius of the curve in the road, m 

Fig.25 also shows the effect the forces G and K d have on the front and rear wheels

Fig 26

The forces on the front wheel and distances referred to below are given in Fig. 26. Equilibrium is obtained when

Eq 6

When the vehicle is about to overturn, the forces Ki and Kai on the inside

wheel are zero, which gives Ke = 2 K, and, since K = xG /2 then Kae =( b/h) K Equation 6 may also be applied to the rear wheels if factor x is replaced by (1 – x). If conditions of friction are assumed to be the same for the outside and the inside wheel the axial forces will be

Eq 7

Using the radial and axial forces obtained in Equation 6 and 7 the bearing loads when negotiating corners can be calculated as follows. For the outside wheel hub bearings

Eq 8

Where Kae (direction I-II, case 2b or 2c, from 'Axial loading of taper roller bearings' table in taper bearing section of SKF General Catalogue. For the inside wheel hub bearing

Eq 9

Where Kai (direction II-I, case 1b or 1c, from 'Axial loading of taper roller bearings' table in taper bearing section of SKF General Catalogue. Normally it is assumed the Kd/G = 0,25, which applies when for instance driving at a speed of 40 km/h round a curve having a radius of 50 m or at 20 km/h round a curve having a radius of 12 m. If, in addition, h/b = 0,5 Equations 6 and 7 give

The equivalent bearing loads for bearing I when driving straight ahead (PI1), round a left-hand curve (PI2) and round a right-hand curve (PI3) are used to determine the mean equivalent load PIm. If it is assumed that 90 per cent of the route is straight, 5 per cent curved to the left and 5 percent curved to the right, therefore

Eq 10

For bearing II the loads are calculated similarly. 

Finally, if the rolling radius of the wheels is RH mm, the bearing life will be

Eq 11

This simplified wheel calculation is offered as a guide for bearing selection. SKF employ advanced calculation programs to more accurately determine bearing life and performance.

Source link SKF Racing - Calculation of Wheel Bearings Loads - PDFCOFFEE.COM

Fig 27

8- Standards

· IATF 16949: The core quality management standard required for automotive production parts.

· ABEC Standards: The Annular Bearing Engineering Committee scale grades the precision and tolerances of industrial and vehicular bearings.

RBEC Standards : RBEC (Roller Bearing Engineers Committee) standards define tolerance classes for roller bearings, just as ABEC standards apply to ball bearings

ABEC vs ISO bearing tolerance class: the full cross-standard chart

Precision increases from left to right in every row.