## Understanding Tire and Wheel Size Measurements
### Determining Tire Size
Tire size is typically displayed in a series of numbers and letters, such as “235/60R18 103H”. This code provides specific information about the tire’s width, aspect ratio, construction, wheel diameter, and load and speed ratings.
Width (235): Measured in millimeters from sidewall to sidewall.
Aspect Ratio (60): Expressed as a percentage, representing the tire’s height-to-width ratio. In this example, the tire’s height is 60% of its width (235 x 0.60 = 141 mm).
Construction (R): Indicates the tire’s construction type. “R” stands for radial, the most common construction method today.
Wheel Diameter (18): Measured in inches from bead seat to bead seat.
Load Index (103): A code representing the maximum load capacity of the tire.
Speed Rating (H): A letter code indicating the maximum safe operating speed for the tire.
### Measuring Tire Size
Using a Measuring Tape:
1. Place the tape measure across the widest part of the tire (sidewall to sidewall).
2. Measure the distance in millimeters.
Using a Tire Gauge:
1. Insert the tire gauge into the indicated spot on the tire.
2. Read the measurement displayed on the gauge.
### Wheel Size Measurement
Wheel size is typically displayed in a two-part format, such as “18×8.5”.
Diameter (18): Measured in inches from the center of the wheel to its outer edge.
Width (8.5): Measured in inches, representing the distance between the inside edges of the bead seats.
### Measuring Wheel Size
Using a Measuring Tape:
1. Place the tape measure across the wheel’s diameter from one edge to the opposite edge.
2. Measure the distance in inches.
Using a Wheel Gauge:
1. Place the wheel gauge on the tire, ensuring it is centered.
2. Read the diameter and width measurements displayed on the gauge.
### Tire and Wheel Fitment Considerations
Diameter: The tire’s diameter should be matched to the wheel’s diameter.
Width: The tire’s width should be compatible with the wheel’s width.
Offset: The wheel’s offset determines the distance between the wheel’s mounting surface and its center. Different offsets can affect the vehicle’s appearance, handling, and tire clearance.
### Safety Precautions
Always refer to the vehicle’s owner’s manual for recommended tire and wheel sizes.
Use only tires and wheels that are designed to fit the vehicle.
Mismatched or incompatible sizes can affect vehicle safety, performance, and durability.
Regularly check tire pressure and perform visual inspections for any signs of damage.
