As you drive around Worcester, you might've noticed the mysterious string of letters and numbers on your tires. What do the numbers on tires mean? Keep reading to find out, thanks to the service team at Long Cadillac!
What Do Tire Numbers Mean?
Every tire has a special code on its sidewall indicating its size, type, performance metrics, and purpose. Make sure to use the right tires for your Southborough drives - not only to help your tires last, but to keep you safe on the road as well.
Determining Tire Number Meanings by Example
The best way to break down a tire number's meaning is to use an example. The rest of this article will use the following code:
P 215/75 R 15 95H
Tire Application
Some tires have a letter in front describing the tire's intended use, such as:
- P (P-metric) tires have been designed for use on passenger cars, such as cars, minivans, SUVs, and some pickup trucks. These are designed for a smooth ride, good handling, and long tread life.
- LT (Light truck) tires have been designed for heavier loads, towing, or off-roading. As the name implies, these are most often installed on light trucks.
- ST (Special trailer) tires are only for use on travel trailers, fifth wheels, and other trailers. They've been designed for higher load carrying capacity, but not for steering-which is why you don't want them on your drive wheels.
What Do Tire Numbers Mean Without a Letter at the Front?
Some tires don't have a letter at the front. These tires are called metric or Euro-metric tires, and generally have the same applications as P-metric tires. However, Euro-metric tires generally have a higher load-bearing capacity than P-metrics.
Tire Width
The first number-215 in our example-is the tire's width in millimeters. So, our example tire is 215mm wide from sidewall to sidewall.
Aspect Ratio
The 75 tells us the tire's aspect ratio, or the ratio between its cross-section height to its width. Our example tire is 75% as tall, from the inside rim to the outside, as it is wide.
Construction
The next letter indicates how the tire has been made. There are a few different ways that modern tires are built:
- R - Radial construction
- B - Bias-ply construction
- D - Diagonal construction
As you can see, the example tire indicated above has been radially constructed.
Rim Diameter
Next up, the tire number has an indication of its rim diameter, in inches. Our example tire has been made to fit a 15-inch diameter wheel.
Load Index
The 95 indicates the tire's load index, or how much weight it can support when properly inflated. For passenger vehicles, these numbers should be between 75-105.
Speed Rating
Finally, a letter between A-Z is used to indicate the tire's maximum safe speed. In our example, the H indicates a maximum speed of 130 miles per hour.
How to Check Tire Pressure
Regardless of your tires' rating, you can help them last as long as possible by keeping them properly inflated on your Framingham drives. Checking your tire pressure manually is pretty easy - but most newer vehicles have an automatic Tire Pressure Monitoring System (TPMS) that will notify you when your tire is under or over inflated.
You can top off your tires yourself at a service station, or bring your Alfa Romeo to our service center for a top-off along with your routine maintenance!
Turn to Long Cadillac for All Your Maintenance Needs
If you need new tires, brake maintenance, an oil change, or any other service your vehicle needs, bring it to Long Cadillac for all of your maintenance and parts needs!
We make it easy to schedule service on our website, and our rotating service specials mean you can save even more when you bring your car to us! Plus, you can always contact us online with any questions you have about what tire numbers mean or anything else.
