The moment you know when to replace tires is the moment the need to understand a truckload of information hits your head. How will you know how to discover the right one?
If you are going to buy new tires, you need to know how to find the tire size on your car. This will not only let you obtain the fitting tire for your vehicle but also save you from a failed purchase.
Often, you will find the numbers located on the owner’s manual or on the car door jamb. These are essential numbers for you to understand how tire sizing works.
So when should you replace tires? Only when you know your replacement tire is going to match the specs of your vehicle. Let’s get started!
How to Find Tire Size on Car
A pressing question that we get is, when do tires need to be replaced? Only when your current tire has taken it all and after you understand the meaning of the following:
Suppose a car has a number sequence as follows: P226/80R16 97H. The number sequence begins with the letter P, which gives the metric sizing. The Metric sizing is the true indication of the tire type.
If you see a P-Metric, it implies that the tire is for Passenger Cars. Most Cars, SUVs, and Light-Duty Trucks weighing less than half a tonne usually take a P-Metric tire. If no letter is present before the Tire Width, then the tire follows a passenger European Metric and will look like this 226/70R16 95H.
If you own heavy-duty Light Trucks, you will use an LT-designation tire, like LT246/75R17 120/116R or a Euro-Metric Commercial (C-type) tire, such as 23/65R16C 121/119R; meant specially for them as they carry heavy cargo.
There are also Temporary Spares, which start with a “T”. Again if you see a tire size that starts with the joint letter “ST”, it means “special trailer” and it is for terrain use only.
The first number that you see appearing after the letter is a measure of the Tire Width in millimeters. In P226/80R16 97H sequence, 226 stands for a passenger vehicle tire with a nominal width of 226 mm.
Just after the slash, the numbers that you see are the aspect ratio shown in percentage. In this case, P226/80R16 97H, the tire has an 80% aspect ratio, which means that for your tire, the height of the rim is 80% its width.
When the ratios are lower, say, in the 65 series, you get riding harshness but also better handling performance than above the 75 series.
The sidewall can have 2 common kinds of construction: Radial (R) or Diagonal/Bias Ply (D)/(B). In the USA, Radial tires that have an orientation of radial-ply cords are more common. If your car has a reading similar to P226/80R16 97H, the tire has a Radial construction.
The next two numbers that you will see indicates the diameter of the rim in which the tire can sit in inches. So in the reading P226/80R16 97H, a 16-inch diameter rim will be required if you plan to purchase this tire. Note that this is in diameter, not radius!
Now that you are clear till the rim/wheel diameter, you will find the load index separated by a space in the middle. This tells you in pounds how much weight your car can support when you have it fully inflated.
Now take a look at this indication P226/80R16 97H. Here the number 79 falls within the range of 1-150. So the car can carry a load of 99 to 7385 lbs. For cars that can carry an extra load, the reading would say P226/80R16 97H XL.
However, in P-Metric and Euro-Metric, the range differs, implying different load capacities for the same numbers.
If you have a heavy-duty light truck, the readings will have two load indexes, like this: LT254/75R20 120/115R. Here, the second index is for use in a dual tire application.
The Speed Rating implies the speed capability of the tire under lab tests. In the sequence P226/80R16 97S, the indication is that the S is up to 112 mph. If your tire was rated an R, it would imply a speed rating of up to 106 mph.
If you want off-road tires, you need to be aware of the floatation sizing. These tires are more like LT tires. However, they can’t be used for dual applications.
Here, the number sequence looks like 35×12.50R17LT, where the first number reads the overall diameter in inches, then the section width in inches, then the aspect ratio followed by the construction (R/B), and after that the rim diameter.
In the end, you have the metric sizing: LT or C-type. You will also find only one load index and the same speed ratings here.
This symbol indicates that the tire you own is compliant with Federal Motor Vehicle Safety Standards of the United States.
Tire Identification Number
The Tire Identification number can answer for you how long these car tires last. On the tire, you get a series of letters and number combinations after the bolded word, DOT. 12 such letters and numbers comprise the TIN or Tire Identification Number. This gives you the week and year of tire manufacturing.
So if you wanted to know how often to change tires, have them inspected 6 years from that date and completely swapped on the 10th year, irrespective of the tread.
Uniform Tire Quality Grading
Last but not least, the UTQ Grading measures the comparative performance of the tires in summer and all-season categories. The grading happens on Tread, Traction, and Temperature to generate data on tire wearing, how well it stops on wet pavement, and its resistance to heat.
Speaking of the grading, check out our milestar ms932 sport review for excellent cornering performance and traction that can give high-end tire brands tough competition!
So this is how you’re supposed to find tire size on a car! Finding the right size for your vehicle can be a tough call when you don’t know what you’re reading or seeing on the tires. But once you understand what the specifications mean, then you can get the right tire for your vehicle with ease!