CAR AC HELP · PHOENIX, AZ
How to Read a Tire Sidewall: Every Number Explained
Updated October 2026 · Written by the techs at The Junkie Garage
The size string: P225/65R17 95H
Every tire's size is printed on the sidewall in one string, and each chunk means something. Using P225/65R17 95H: P = passenger-car tire (LT = light truck). 225 = the section width in millimeters, sidewall to sidewall. 65 = the aspect ratio — the sidewall height as a percentage of the width, so this sidewall is 65% of 225mm. R = radial construction. 17 = the wheel diameter in inches the tire fits. 95H = the load index and speed rating, explained below.
Load index and speed rating
The load index is a lookup number, not a weight: 95 corresponds to roughly 1,521 pounds per tire. Multiply by four (or follow the vehicle placard) and you see why a tiny-looking number matters. The speed rating letter (H = 130 mph, V = 149, T = 118, common examples) is really a heat-dissipation rating — the tire's sustained-speed capability. Your vehicle's placard, on the driver's door jamb, lists the exact size, load index and pressure the manufacturer engineered for the car; matching it exactly is always correct.
The DOT date code — the number people miss
On one sidewall, look for 'DOT' followed by letters and four digits: the last four are the tire's birthday — week and year. '2324' means the 23rd week of 2024. This matters because rubber ages even sitting in a warehouse: most manufacturers and safety experts consider six years from date of manufacture a sensible ceiling regardless of tread. A 'new' tire you just bought could already be two or three years old — legal to sell, but worth knowing.
Other markings worth knowing
M+S (mud and snow) or the three-peak-mountain-snowflake mark seasonal capability — the snowflake is the serious winter rating, M+S mostly isn't. 'Max Load' and 'Max Press' list the tire's absolute limits — the max pressure is NOT your driving pressure; the placard on the door jamb is. The Uniform Tire Quality Grades (treadwear, traction, temperature) allow rough comparisons between models, and XL (extra load) tires carry a higher load index at higher pressure — never mix XL and standard on the same axle.
What actually matters when replacing
Match the placard size and load rating exactly, choose the speed rating the placard calls for or higher, check the DOT date on what's being installed, and never mix tread depths or models on the same axle. When in doubt, the door-jamb placard answers every question the sidewall raises.
Make them lastRotation is the cheapest tire maintenance there is — here's the interval guide.Frequently asked questions
What does 225/65R17 mean on a tire?
225mm section width, a sidewall 65% as tall as it is wide, radial construction, fitting a 17-inch wheel. The door-jamb placard lists your exact size.
How do I know how old my tires are?
Find the DOT code on the sidewall: the last four digits are week and year of manufacture — '1525' means made in April 2025. Most experts recommend replacing tires at six years of age regardless of tread.
Can I use a different tire size than the placard says?
The placard size is what the speedometer, ABS calibration and load capacity were engineered for. Plus-size wheel setups are a deliberate, informed modification — otherwise match the placard exactly.
What's the difference between H and V speed ratings?
H is rated to 130 mph, V to 149. It's really heat-dissipation capability at sustained speed. Use the placard's rating or higher — going lower reduces safety margin even in everyday driving.
Need your car AC looked at?
The Junkie Garage is a community shop in Phoenix, AZ. More help from the main site: