A sidewall such as 225/45 R18 95Y is a compact specification. Read the complete code—not only the rim diameter—and confirm it against the tyre placard, owner’s handbook, or a professional fitment check.
Start with the complete code
225 is the nominal section width in millimetres. 45 is the aspect ratio: the sidewall height is approximately 45 percent of the width. R describes radial construction, and 18 is the compatible wheel diameter in inches.
The load index, 95 in this example, maps to carrying capacity under specified conditions. The Y speed symbol represents a tested speed category. Do not reduce either requirement below the vehicle manufacturer’s specification unless qualified advice and applicable rules permit it.
Check the vehicle
Use the placard in the driver’s door opening, fuel door, or location identified in the handbook. Front and rear sizes may differ. Confirm the year, model, trim, drivetrain, brake package, and factory options. A tyre already on a used or modified vehicle is not proof that it is correct.
Additional markings
XL, run-flat designations, winter or severe-snow symbols, OE homologation marks, directional arrows, asymmetric markings, and manufacturing codes may affect selection and installation.
Checklist
- Match size, load index, and speed symbol.
- Check whether front and rear differ.
- Confirm XL, run-flat, or OE requirements.
- Use the vehicle placard pressure after installation.
- Ask for a fitment review if the vehicle is modified.
This guide is general information, not a substitute for vehicle and product instructions or professional inspection.