Every tire carries its size on the sidewall in a short code. Once you can read it, buying tires, especially used ones, gets much easier. We will use a common example: 225/45R18 95V.
Where to find the right size for your vehicle
Do not start with the tires currently on your car. A previous owner may have put on the wrong size. Start with:
- The tire placard on the driver's door jamb (sometimes in the glove box or fuel door).
- Your owner's manual.
Some vehicles list different sizes for the front and rear, or different sizes for different trim levels. Use the one that matches your vehicle.
The code, piece by piece
225 is the width of the tire in millimetres, sidewall to sidewall.
45 is the aspect ratio: the sidewall height as a percentage of the width. Here the sidewall is 45% of 225 mm. A lower number means a shorter, "low-profile" sidewall.
R means radial construction, which is nearly every passenger tire today.
18 is the rim diameter in inches. This must match your wheel exactly. An 18-inch tire only fits an 18-inch rim.
95 is the load index, a code for how much weight each tire can carry. 95 works out to 690 kg per tire. Your replacement tires need a load index equal to or higher than what your vehicle calls for.
V is the speed rating, the maximum sustained speed the tire is designed for. Common ratings are T, H, V and W. Winter tires often carry a lower speed rating than the summer tires that came on the car. Check your owner's manual for what is allowed on your vehicle.
Other markings worth knowing
- P or LT before the size (for example P225/45R18 or LT265/70R17). P is passenger, LT is light truck. LT tires are built differently and are inflated differently. Do not mix them on the same vehicle without checking.
- XL or Extra Load means a higher load capacity at a higher pressure.
- Three-peak mountain snowflake symbol: a tire that meets a winter traction standard.
- M+S (mud and snow): common on all-season tires. It is not the same as a winter tire.
- DOT code: the last four digits are the date the tire was made. See How to read a tire's date code.
What this means for our prices
Tire change pricing at our garage in Laurel, South Edmonton is based on vehicle type and rim size, the number after the R. A sedan on 17-inch rims and a sedan on 18-inch rims are priced differently, and low-profile tires (short sidewalls, usually an aspect ratio of 45 or lower) take more care to mount, which is why they carry a small add-on.
Not sure?
Send us a photo of the sidewall and the door-jamb sticker when you book. Keep in mind that when you supply your own tires, matching them to your vehicle is your responsibility. See Will these tires fit my car?