Wheels, Hubs, and Tires

Chapter Introduction

This chapter covers all the wheel-end systems of transport trailers: wheels, hubs, and tires. For the Red Seal exam, you must master not only disassembly and assembly procedures, but also load calculations, wear tolerances, torque specifications, and applicable Canadian standards. This chapter is designed to be studied in a linear fashion; each section builds on the previous one.

Hub Components and Functions

Definition and Role of the Hub

The hub is the central component of the wheel assembly. It supports the weight of the trailer, transmits braking torque (if equipped with wheel brakes), and ensures the rotation of the wheel around the axle. The hub is mounted on bearings (usually two per hub) that allow it to rotate freely around the axle spindle.

Types of Hubs

Type	Key Characteristic	Typical Application
Tapered roller bearing hub	Two opposed tapered bearings, adjustment by nut	Utility trailers, single axles
Cylindrical roller bearing hub	No axial play, interference fit	Heavy trailers, tandem axles
Unitized hub	Pre-adjusted, sealed, non-adjustable bearings	Modern trailers, commercial fleets
Integrated drum hub	Brake drum cast with the hub	Trailers with hydraulic or air brakes

Internal Hub Components

The hub contains:

Two bearings: an inner bearing (larger) and an outer bearing (smaller).

A seal (oil seal): located at the rear of the hub, prevents grease leakage and contaminant entry.

A spacer (if applicable): maintains the spacing between bearings.

An adjusting nut: with or without a cotter pin, depending on the axle type.

A hub cap (or dust cap): protects the end of the axle and retains grease.

Axle Spindle

The spindle is the machined end of the axle on which the bearings are assembled. It features:

A shoulder (stop) for the inner bearing.

Threads for the adjusting nut.

A bore for the cotter pin (on manually adjustable axles).

Exam Point: The end play of a tapered roller bearing hub must be 0.001 to 0.005 inches (0.025 to 0.127 mm) for a standard trailer axle. Excessive play causes premature wear and overheating.

Wheel Bearings

Types of Bearings

Trailer wheel bearings are almost exclusively tapered roller bearings. They are designed to support combined radial and axial loads. Each bearing consists of:

An inner race (cone).

An outer race (cup).

Tapered rollers.

A retainer cage.

Identification and Dimensions

Each bearing is identified by a standard number (e.g., LM67048 for the inner cone, LM67010 for the cup). The following table gives common correspondences for trailer axles:

Axle Capacity (lb)	Inner Bearing	Outer Bearing
3,500	LM67048 / LM67010	LM11949 / LM11910
5,200	25580 / 25520	15123 / 15245
7,000	25580 / 25520	14125A / 14276
10,000	3780 / 3720	25580 / 25520

Important: Cones and cups must always be replaced as matched sets, and never mixed between manufacturers. Bearings from different brands are not interchangeable even if the numbers appear identical.

Tapered Bearing Adjustment

The standard adjustment procedure is as follows:

37.Clean and inspect all components.

38.Grease the bearings with lithium or molybdenum grease (per manufacturer specification).

39.Install the inner bearing into the hub, then the seal.

40.Mount the hub onto the spindle.

41.Install the outer bearing and washer.

42.Thread the adjusting nut by hand until contact.

43.Tighten the nut to 50 lb-ft (68 N·m) while rotating the hub to seat the rollers.

44.Back the nut off one-quarter turn (90°).

45.Tighten by hand until light contact.

46.Install the cotter pin. If the hole does not align, loosen the nut slightly (never tighten further).

End Play Calculation: The final play must be checked with a dial indicator. The reading must be between 0.001 and 0.005 inches. A play greater than 0.005 inches indicates incorrect adjustment or worn bearings.

Bearing Failure Detection

Signs of failure include:

Grinding or clicking noise during rotation.

Hub overheating (detected by touch or infrared thermography).

Excessive play detected during inspection.

Burn marks or blue discoloration on rollers or races.

Spalling on bearing surfaces.

Exam Trap: A bearing showing blue discoloration is definitively heat-damaged and must be replaced. It cannot be reused, even if the geometry appears intact.

Trailer Tires

Tire Anatomy

A trailer tire consists of:

The tread: surface in contact with the road.

The shoulders: transition zones between the tread and the sidewalls.

The sidewalls: protect the carcass and carry the information.

The carcass: structure of cords (steel, polyester, nylon) that provides strength.

The beads: ensure sealing with the rim.

The bead wire: steel cable that holds the tire on the rim.

Load and Speed Indices

Each tire carries a Load Index and a Speed Symbol molded on the sidewall.

Speed Symbol	Maximum Speed (km/h)
L	120
M	130
N	140
P	150
Q	160
R	170
S	180
T	190

Reading Example: A tire marked "225/75R15 117/114R" has a load index of 117 in single application (2,833 lb) and 114 in dual application (2,601 lb), with a maximum speed of 170 km/h.

Inflation Pressure

Inflation pressure is determined by:

72.The maximum load per tire (based on the axle and number of tires).

73.The tire manufacturer's load table.

74.The intended operating speed.

General Rule: Increasing pressure increases load capacity but reduces the contact patch. Insufficient pressure causes overheating and sudden failure.

Pressure Calculation for a Given Load:

Load per tire = Total weight on the axle ÷ Number of tires on the axle.

Consult the manufacturer's table for the corresponding minimum pressure.

Add 10% margin for temperature variations and measurement errors.

Tire Wear

The minimum legal tread depth for trailer tires is 2/32 of an inch (1.6 mm) in all major grooves. However, for commercial trailers, a depth of 4/32 inch (3.2 mm) is recommended for steering tires and 2/32 inch for trailer tires.

Wear Patterns and Causes:

Wear Pattern	Probable Cause
Center wear	Overinflation
Wear on both shoulders	Underinflation
Wear on one shoulder only	Incorrect alignment (camber)
Sawtooth wear	Incorrect toe alignment
Localized wear (flat spots)	Wheel lock-up, imbalance
Cupping (diagonal wear)	Defective suspension

Balancing and Alignment

Imbalance of trailer wheels must be corrected by adding balance weights. Static imbalance (single plane) and dynamic imbalance (two planes) must be checked. For trailers, the maximum allowable imbalance is generally 0.5 oz (14 g) per side.

Alignment of trailer axles must be checked:

Parallelism: maximum deviation of 1/16 of an inch (1.6 mm) over the distance between axles.

Camber: 0° to +0.5° (slightly positive).

Toe: 0 to 1/16 of an inch (0 to 1.6 mm) in positive toe.

Rims and Wheel Fastening

Types of Rims

Type	Description	Application
Drop center rim	Most common, central groove for mounting	Tubeless tires
Semi-drop center rim	Shallow groove	Tube-type tires
Flat base rim	Flat surface, locking ring	Heavy-duty tires
Multi-piece rim	Multiple components (ring, lock)	Prohibited on highway trailers

Important: Multi-piece rims are prohibited on trailers operating on public roads in Canada due to the risk of explosion during inflation.

Wheel Bolts and Nuts

Wheel nuts are classified by:

Thread diameter: 1/2", 9/16", 5/8", 3/4".

Thread pitch: UNC (coarse thread) or UNF (fine thread).

Seat shape: conical (60°), spherical (ball seat), or flat.

Seat Type	Angle	Application
Conical	60°	Standard steel wheels
Spherical	90°	Alloy wheels
Flat	0°	Heavy-duty wheels with washer

Wheel Nut Torque

Torque is critical. Insufficient tightening allows loosening; excessive tightening deforms the rim or breaks the studs.

Stud Diameter	Torque (lb-ft)	Torque (N·m)
1/2"	75 – 85	102 – 115
9/16"	110 – 130	149 – 176
5/8"	150 – 180	203 – 244
3/4"	200 – 250	271 – 339

Tightening Procedure:

105.Tighten all nuts by hand.

106.Tighten in a star (crisscross) pattern to 50% of final torque.

107.Tighten in a star pattern to 100% of final torque.

108.Re-check after 80 to 160 km of service.

Exam Trap: Never grease the threads of studs or nuts. Lubrication changes the friction torque and can lead to over-tightening (up to 30% error). Nuts must be dry and clean.

Canadian Standards and Regulations

Canadian Electrical Code, Part I

Although this chapter primarily concerns electrical systems, the Canadian Electrical Code, Part I (CSA C22.2) applies to trailers with respect to the wiring of tire pressure monitoring systems (TPMS) and hub temperature monitoring systems. The relevant provisions require that all wiring be protected against abrasion and mechanical damage (Rule 8-200 for conductors in vehicles).

CSA Standards for Tires and Wheels

The CSA D265 standard (Travel Trailers) and the CSA B620 standard (Dangerous Goods Transport Tanks) contain specific requirements for tires, rims, and hubs. These standards require, among other things:

Tires with a load index at least 10% higher than the maximum load per tire.

Rims conforming to the vehicle manufacturer's specifications.

A tire pressure monitoring system (TPMS) mandatory for trailers over 4,536 kg (10,000 lb).

Canada Motor Vehicle Safety Regulations (CMVSR)

The CMVSR establishes federal requirements for tires and wheels. Relevant sections include:

Section 110: Tire requirements (dimensions, load indices).

Section 120: Rim requirements (strength, dimensions).

Section 121: Brake system requirements (interaction with hubs).

Exam Point: The CMVSR requires trailer tires to have a speed rating of at least L (120 km/h) for normal highway use.

Transport Canada and Defect Notices

Transport Canada publishes defect notices for tires and wheels. The technician must consult the defect notice database before repairing or replacing components. Common defects concern:

Tread detachment.

Sidewall cracks.

Alloy rim failures.

Inspection and Maintenance Procedures

Periodic Hub Inspection

Inspection must be performed at every preventive maintenance interval (generally every 40,000 km or 6 months):

134.Visual check: Look for grease leaks around the seal, hub cracks, missing caps.

135.Play check: Lift the wheel and check axial and radial play.

136.Temperature check: After a trip, each hub should be at a comparable temperature. A difference greater than 15 °C indicates a problem.

137.Bearing check: Complete disassembly, solvent cleaning, inspection of races and rollers.

138.Seal replacement: Systematic during disassembly.

Tire Inspection

Tire inspection includes:

Pressure: Check cold, with a calibrated gauge.

Tread depth: Use a depth gauge.

Irregular wear: Identify patterns and correct the cause.

Damage: Cuts, bulges, nails, cracks.

Age: A tire over 6 years old must be replaced, even if the tread is good. The manufacturing date is indicated by the DOT code (the last 4 digits indicate the week and year).

DOT Code Example: DOT 4321 means manufactured in the 43rd week of 2021.

Tire Replacement Procedure

148.Lift the trailer with a hydraulic jack at the appropriate lifting point.

149.Place safety stands.

150.Loosen the wheel nuts half a turn before lifting completely.

151.Remove the nuts and the wheel.

152.Demount the tire from the rim using a tire changing machine.

153.Inspect the rim for deformation, corrosion, cracks.

154.Mount the new tire respecting the rotation direction (if directional).

155.Inflate to the recommended pressure (never above 40 psi for initial inflation before inspection).

156.Balance the wheel.

157.Reinstall and tighten the nuts to the specified torque.

Useful Calculations and Conversions

Pressure Conversion

Unit	Equivalent
1 psi	6.895 kPa
1 bar	100 kPa
1 kPa	0.145 psi
1 atm	101.325 kPa

Load Per Tire Calculation

Formula:

Load per tire = (Total weight on the axle) ÷ (Number of tires)

Example: A tandem trailer with a total weight of 14,000 lb on both axles.

Weight per axle = 14,000 ÷ 2 = 7,000 lb.

Weight per tire (4 tires per axle) = 7,000 ÷ 4 = 1,750 lb.

Choose a tire with a load index of at least 1,750 lb (index 112 or higher).

Rolling Circumference Calculation

Formula: C = π × D

Where D is the outside diameter of the tire in inches.

Example: Tire 225/75R15.

Sidewall height = 225 mm × 0.75 = 168.75 mm = 6.64 inches.

Total diameter = 15 + (2 × 6.64) = 28.28 inches.

Circumference = π × 28.28 = 88.84 inches = 2.26 meters.

Torque Conversion

Unit	Equivalent
1 lb-ft	1.356 N·m
1 N·m	0.738 lb-ft

Pitfalls to Avoid

Frequent Exam Errors

181.Confusing end play and radial play: End play is movement along the axle axis; radial play is movement perpendicular to it. Tapered bearing adjustment controls only end play.

182.Forgetting the 90° rule: After the initial tightening to 50 lb-ft, the nut must be backed off one-quarter turn, then re-tightened by hand. Never tighten further to align the cotter pin.

183.Using bearings from different manufacturers: Cones and cups must be from the same brand and batch. Mixing manufacturers is a major cause of premature failure.

184.Ignoring the tire manufacturing date: A tire may look new but be over 6 years old. The DOT code is mandatory knowledge for the exam.

185.Greasing wheel nut threads: This is the most costly error. Lubrication falsifies the torque reading and can cause stud breakage.

186.Confusing single and dual load indices: A tire marked 117/114 has a capacity of 2,833 lb in single application but only 2,601 lb in dual application. Using the wrong index can cause overload.

187.Forgetting the hub temperature check: A hub hotter than the others indicates a tight bearing or a dragging brake. This check is systematic during stops.

188.Not replacing the seal during disassembly: The seal is a single-use component. Its reuse is professional malpractice.

189.Using incorrect torque for alloy wheels: Alloy wheels often require a different torque than steel wheels. Always consult the manufacturer's specifications.

190.Ignoring Transport Canada defect notices: The technician must check notices before any major repair.

Summary

Key Points to Remember

The hub supports the load and transmits braking torque. It contains two tapered bearings (inner and outer) and a seal.

End play of tapered bearings must be 0.001 to 0.005 inches (0.025 to 0.127 mm).

Standard adjustment procedure: tighten to 50 lb-ft, back off 90°, re-tighten by hand, install cotter pin.

Bearings must be replaced as matched sets, never mixed between brands.

Inflation pressure determines load capacity. Insufficient pressure causes overheating and failure.

The minimum legal tread depth is 2/32 inch (1.6 mm).

Multi-piece rims are prohibited on public roads.

Wheel nut torque must be respected without lubricating the threads.

The CMVSR requires a speed rating of at least L (120 km/h) for trailer tires.

TPMS is mandatory for trailers over 4,536 kg (10,000 lb).

A tire over 6 years old must be replaced, regardless of tread depth.

Checking hub temperature after a trip is an essential diagnostic procedure.

Essential Formulas

Load per tire = Weight on axle ÷ Number of tires.

Circumference = π × Diameter.

Conversions: 1 lb-ft = 1.356 N·m; 1 psi = 6.895 kPa.

Final Checks Before the Exam

[ ] I know the bearing numbers for axles from 3,500 to 10,000 lb.

[ ] I can explain the 10-step bearing adjustment procedure.

[ ] I know the tire wear patterns and their causes.

[ ] I can read a DOT code and calculate a tire's age.

[ ] I know the torque values for studs from 1/2" to 3/4".

[ ] I can convert pressure and torque units.

[ ] I know the requirements of the CMVSR and applicable CSA standards.

This chapter covers all the theoretical and practical knowledge necessary to pass the "Wheels, Hubs, and Tires" section of the Red Seal exam. Mastering these concepts, combined with regular practice of calculations and procedures, will allow you to approach the exam with confidence.

Wheels, Hubs, and Tires