What the numbers on your tire actually mean
245/40R19 95W looks like a serial number. It is really five separate pieces of information, and once you can read them you will never order the wrong tire again.
Ryan Grubbs · 2 min read
Every tire has its size moulded into the sidewall. It looks like gibberish until someone breaks it down, so here it is, using 245/40R19 95W as the example.
245 is the width
That is the width of the tread in millimetres, measured across the tire. Bigger number, wider tire. It has nothing to do with your wheel size.
40 is the aspect ratio
This one confuses people because it is a percentage, not a measurement. The sidewall height is 40 percent of the width. So on a 245 wide tire, the sidewall is about 98mm tall.
A low number like 35 or 40 means a short, stiff sidewall. It looks good and handles sharply, and it is also why low profile tires get destroyed by potholes. A number like 65 or 70 means a taller sidewall with more cushion.
R means radial
Almost every tire sold today is radial. If you see a D instead, it is a bias ply, usually on a trailer.
19 is the wheel diameter
In inches, not millimetres, because tire sizing is a mix of two measuring systems and nobody has ever fixed it. This must match your wheel exactly. A 19 inch tire does not go on an 18 inch wheel, no matter what else matches.
95W is the load and speed rating
95 is the load index, which maps to how much weight the tire can carry. W is the speed rating. You can go up from what the manufacturer specified, but going down is a bad idea, especially on a heavy vehicle.
Where to find it
Look at the outer sidewall of any tire on the car. It is moulded in, usually the largest text there. There is also a sticker in the driver's door jamb showing the size the vehicle came with from the factory, which is worth checking if your current tires might be the wrong size.
One catch: staggered fitments
Some performance cars run wider tires at the back than the front. Check one front and one rear before you order. If they are different, you need two sizes.
Once you have the size, you can search it on our site and see real prices for tires that fit, along with what it costs to have them fitted at your house.
Questions
While we are on the subject
Can I fit a different size than the sticker says?
Sometimes, but it needs care. Changing the overall diameter affects your speedometer and, on some vehicles, the traction control. Call us with the vehicle and the size you are considering and we will tell you straight whether it works.
Do all four tires have to match?
They should match in size and ideally in model, especially on all wheel drive vehicles where mismatched rolling diameters can damage the drivetrain. Front and rear can differ on a staggered setup, but left and right on the same axle must match.
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