Tire size calculator

Type the size from your tire’s sidewall. Add a second size to see how it compares, including how far off your speedometer would read.

How old are my tires?

Find “DOT” on the sidewall. The last four digits are the week and year it was made.

Speed ratings

The letter after the load number, like the H in 102H, is the top speed the tire is rated for.

Q: 99 mph
R: 106 mph
S: 112 mph
T: 118 mph
U: 124 mph
H: 130 mph
V: 149 mph
W: 168 mph
Y: 186 mph

A speed rating isn’t a recommendation to drive that fast. Match or exceed the rating your car calls for.

How to read a tire size

Take P225/65R17 102H:

P: passenger tire. LT is light truck (higher load capacity), T is a temporary spare, and no letter means Euro-metric.
225: the tire’s width in millimeters.
65: the aspect ratio. The sidewall is 65% as tall as the tire is wide.
R: radial construction.
17: the wheel diameter in inches. This has to match your wheel exactly.
102: the load index. Never fit a lower load index than your vehicle specifies.
H: the speed rating (130 mph).

Can I put a different size on my car?

Stick to the sizes listed on your driver’s door-jamb sticker or in your owner’s manual. Continental warns that sizes that aren’t approved can affect speedometer accuracy, ABS and ground clearance, and that on all-wheel-drive cars mismatched tires can stress the drivetrain. A bigger overall diameter makes the speedometer read low; a smaller one makes it read high.

How old is too old?

Continental says some automakers recommend replacing tires around six years from the date they were made, and that every tire, spares included, should be replaced after ten years. A three-digit DOT date means the tire was made before 2000 and shouldn’t be in service. Your automaker’s guidance comes first. For tread depth, seewhen to replace tires.

Sources:Continental Tire: How to read your tire sidewall; Goodyear: Tire speed ratings. Diameter and speedometer numbers are calculated from the size; real tires vary slightly by brand and tread wear.