Tire Sidewalls
What does the letter R indicate in a tire size such as 225/65R17?
Radial tire construction.
What tool is used to measure tire tread depth?
A tire tread depth gauge.
What tool is used to tighten lug nuts to the manufacturer's specified torque?
A torque wrench.
What machine is used to remove a tire from a wheel and install another tire?
A tire changer.
What is the purpose of balancing a wheel and tire assembly?
To correct mass imbalance that can cause vibration.
In the tire size 225/65R17, what does 225 represent?
The tire's nominal section width in millimeters.
What unit is commonly used to record tire tread depth in the United States?
Thirty-seconds of an inch (1/32").
Why should lug nuts be started by hand?
To reduce the risk of cross-threading or damaging the fasteners.
What must be done before using a bead breaker on a tire?
Completely deflate the tire and verify it has no remaining pressure.
What are the three basic wheel measurements used by the Coats Direct Drive 950 balancer(our balancer in the shop)?
A (offset/distance), W (width), and D (diameter).
In the tire size 225/65R17, what does 65 represent?
The aspect ratio. The sidewall height is 65% of the tire's section width.
Where should you find the vehicle manufacturer's recommended tire inflation pressure?
On the vehicle's tire information placard, commonly on the driver's door jamb, or in the manufacturer's information.
Why are wheel fasteners tightened in a star or crisscross pattern?
To help seat the wheel evenly against the hub.
Why is approved tire mounting lubricant used?
It reduces friction, helps prevent bead damage, and assists with proper mounting and bead seating.
Why must a wheel be correctly centered and secured on a balancer?
Incorrect mounting can produce inaccurate readings and create a safety hazard.
What do the load index and speed rating tell a technician?
The load index identifies the tire's rated load capacity, and the speed rating identifies its rated speed capability under specified conditions.
Why should tread depth be measured at the inner, center, and outer portions of a tire?
To identify uneven wear and determine the tire's condition across its tread.
What information must be checked before selecting a tire rotation pattern?
The manufacturer's rotation instructions and whether the tires are directional, staggered, or otherwise restricted in their placement.
Why must the technician be aware of the TPMS sensor's location when changing a tire?
The bead breaker and mounting tools can damage the sensor if used incorrectly.
What is the difference between clip-on and adhesive wheel weights?
Clip-on weights attach to suitable wheel flanges, while adhesive weights attach to prepared wheel surfaces.
A tire has a DOT manufacture date code of 3424. When was it manufactured?
The 34th week of 2024.
During an inspection, you discover a bulge in a tire's sidewall. What should you do?
Document and report the damage immediately. The tire may have structural damage and should not be considered safe for continued service.
A vehicle has directional tires mounted on wheels, and the tires cannot be dismounted. What rotation restriction normally applies?
They should remain on the same side of the vehicle and can generally be rotated front-to-rear only, provided tire sizes and manufacturer instructions permit it.
A tire bead is not seating properly during inflation. What is the correct response?
Stop inflation, follow the equipment manufacturer's safe deflation and troubleshooting procedures, and inspect the tire and wheel for compatibility, damage, and correct positioning. Never exceed the applicable bead-seating pressure limit.
After installing the indicated balancing weights, what should the technician do before removing the wheel from the machine?
Perform a verification spin and confirm that the wheel meets the balancer's acceptable balance tolerance.