Tires
How to Read Tire Size
Decode sidewall markings and match your door placard.
Reviewed 2026-06-18
Key takeaways
- Placard size beats what's on the sidewall if someone changed wheels.
- P215/55R17 = metric width, aspect ratio, radial, 17-inch wheel.
- Load index and speed rating must meet or exceed placard.
- DOT date shows manufacture week and year.
Example P215/55R17
P = passenger metric. 215 = tread width in mm. 55 = sidewall height as percent of width. R = radial construction. 17 = wheel diameter in inches. Additional marks show load index (e.g. 94) and speed rating (e.g. V).
Placard vs sidewall
Driver door jamb lists OEM size and cold PSI. Sidewall shows what is mounted — they should match unless the vehicle was modified. Always buy replacements to placard spec unless a tire professional approves a plus-size.
Load index and speed rating
Load index is a coded weight capacity — higher is stronger. Speed rating letter (H, V, W, etc.) is max sustained speed capability. Do not downgrade below placard ratings.
DOT date code
Last four digits of DOT block: WWYY week and year made. Avoid buying tires older than six months from shelf; replace at six to ten years regardless of tread.
Plus-sizing basics
Keep overall diameter within about 3% of factory to protect speedometer and ABS. Wider tires need compatible wheel width. A tire shop can confirm fitment before purchase.
Frequently asked questions
What if my tires are different front and rear?
Some staggered sports cars ship different sizes — match per axle and follow manual rotation rules.
Does LT mean light truck?
LT-metric sizes use different load tables than P-metric — do not mix on the same axle.
Sources
- NHTSA TireWise
- Owner manual
Informational only — not a substitute for a qualified technician. How we verify guides