How To Read Your Tires
Different types of vehicles, driving conditions, and preferences in handling and vehicle response all require different types of tires. It is important to understand tire numbers and what tire size and rating are right for your vehicle. The overall performance and safety of your vehicle are very much dependent on the right tires being installed.
The good thing is, determining the correct size and type for your vehicle’s tires, knowing how to read tires, and understanding tire sizes is not difficult.
Where to Find Your Vehicle’s Tire Size
It is important to always make sure that you are following the recommendations for your vehicle’s tire size and specifications. All of this necessary information is readily available and you can find these specific recommendations in several places in or on your vehicle.
You can, of course, find the tire size and rating data of your current tires on the sidewall of the tire itself. This is assuming that they are the proper size currently.
The first place where you can find your vehicle’s manufacturer’s recommended tire size and specifications is in the owner’s manual. Otherwise, the tire size information can also be found in the driver’s side door jamb, on the inside of your glove box door, and on the inside of your gas tank/cap hatch.
Tire Size Explained
The first two things that many people think of when it comes to tire numbers are the width and diameter. Those are indeed two very important aspects of the tire. But other factors should be considered as well when determining the proper tires for your vehicle, driving habits, and preferences.
The letters and numbers that are present on the sidewall of tires tell you everything you need to know about that specific tire. Let’s break down how to read tires:
For example purposes, we’ll use two sets of tire numbers:
P225/60R16 95S and LT235/75R15 96H
The first letter(s) at the beginning of the number sequence is very important and indicates the type of tire it is. A letter ‘P’ indicates that it is intended for passenger cars. These tires are in P-metric sizing and made to certain U.S. standards and load indexes specifically for passenger vehicles, including cars, minivans, SUVs, and some light-duty pickup trucks.
In our other example, an ‘LT’ indicates that the tire is a light truck tire. These tires go by LT-metric sizing and load indexes and are designed for use on vehicles that can carry heavy cargo or pull trailers.
If a tire does not have any letters in front of the numbers, this indicates it is a Euro-metric tire. These tires are made to European tire specifications and often have a different load index than a comparably sized P-metric tire.
A ‘T’, for “temporary”, will be before the number sequence on small spare tires. There is also ‘ST’, or “special trailer”, which indicates the tire is a trailer tire.
When determining the proper tire size for your vehicle, and purchasing new tires, don’t leave your letter off – it’s important!
After any beginning letters, the next three numbers in the sequence are the section width. This refers to the width of the tire tread, measured in millimeters, from sidewall edge to sidewall edge. In the examples above (P225/60R16 95S and LT235/75R15 96H), the section widths are 225mm and 235mm, respectively. So, in general, the larger the number the wider the tire.
The next two numbers, after the slash, are the aspect ratio. This is the sidewall height in comparison to the section width and is expressed like a percentage in the “tire size” number sequence. In the examples above (P225/60R16 95S and LT235/75R15 96H), aspect ratios are 60% and 75%. So, the sidewall heights are 135mm (60% of 225mm) and 176.25mm (75% of 235mm), respectively. The larger the aspect ratio the larger the sidewall height will be.
When the aspect ratio number is lower, like 55 or less, the shorter sidewall on the tire provides improved vehicle handling and steering response.
Internal Tire Construction
After the aspect ratio, you’ll usually see the letter ‘R’. This refers to the tire’s internal construction. The ‘R’ stands for Radial, which is the industry standard in modern tires now. When a tire is a Radial tire, this means the internal ply cords of the tire run radially across the tread perpendicular to the axis of rotation.
The next two numbers in the sequence are the diameter of the rim, in inches. So again, using our examples above (P225/60R16 95S and LT235/75R15 96H), the rim size for these tires is 16 inches and 15 inches, respectively.
After the wheel diameter, there will be a space and then a two or three-digit number. This is the load index. The load index of a tire is the maximum load, or weight, that the individual tire can support when properly inflated. It is referred to as the load “index” because the number is not the actual number of pounds but refers to a digit in the load capacity index. Starting at 1 and ending at 150, the numbers in the load index refer to carrying capacities of 99 to 7385 lbs.
So, when looking at our two examples (P225/60R16 95S and LT235/75R15 96H) the load indices are 95 and 96. This means the carrying capacity of the tire (per tire, not all four) is 1521 lbs and 1565, respectively. It is very important to only have tires installed that have a load index that meets or exceeds your vehicle manufacturer’s recommended specification.
The final letter of the sequence refers to the speed rating. The speed rating is the maximum speed that the properly installed and inflated tire can safely be driven on for extended periods. The letter indicated corresponds to a specific speed capability, in miles per hour, based on standardized laboratory testing. Using our two examples (P225/60R16 95S and LT235/75R15 96H), the speed rating ‘S’ signifies a maximum rating of 112 mph, while a speed rating of ‘H’ means a maximum rating of 130 mph.
Of course, this doesn’t mean that you should drive at these speeds, but these are the top speeds the tires can safely handle.
Usually, you’ll get better handling performance from tires with a higher speed rating. When getting new tires, they should have the same or higher speed rating to maintain vehicle capability. If the vehicle has tires with different speed ratings, you should go by the lowest speed rating to determine the safest top speed of the car.
If you have any questions or need further information on how to read tires, don’t hesitate to contact us today!
Follow the Manufacturer-Recommended Tire Pressure Guidelines
As you can see, making sure that your tires are properly inflated plays a big part in the specifications and performance of a tire. Proper inflation will also help you get the longest life out of your tires. You should always follow the manufacturer-recommended tire pressure guidelines for your vehicle.
The recommended air pressure is actually not displayed on the sidewall of the tire. Often, the tire sidewall will indicate the maximum air pressure specification, which is the maximum psi that the tire can be safely inflated to. But this is a different figure than the recommended tire pressure. You will usually never have your tires inflated to maximum air pressure.
The manufacturer-recommended tire pressure guidelines that should be used for everyday driving will be found in your owner’s manual or on your driver’s side door jamb.
Ramona Tire & Service Centers is Your #1 Source for Tires
With 17 convenient locations and a large selection of quality options, Ramona Tire & Service Centers is your #1 source when you are buying new tires. Our expert technicians can help answer any tire questions you may have, help you determine the proper tire size if needed, and assist you in picking out the perfect tires to meet your driving needs. Book your appointment today to have your new tires installed.
At Ramona Tire & Service Centers, we offer great financing options to help make it easier for you to get the tires or auto repair work done that you need. The Ramona Tire Credit Card provides a dedicated credit line for your vehicle, as well as exclusive benefits such as 6 months no interest financing on services over $150, no annual fee, and low monthly payments.
You can also apply for the Goodyear Credit Card which offers the same benefits and deferred-interest financing along with eligibility for double rebates on Goodyear tire purchases.