Understanding Tire Load Ratings: Decoding Numbers and Symbols

tire rating code

If you’ve ever taken a closer look at the numbers and symbols on your tires and felt like you were deciphering a secret code, you’re not alone. At Big Chief Tire, we’re here to teach you everything you need to know about tire ratings for a smoother and safer ride.

What Are The Safety Ratings On My Tires?

The markings on your vehicle’s tires are there for a reason, and understanding them is key to keeping your ride in top-notch condition. Here’s what you need to know about your tires’ safety ratings and why they’re there:

Aspect Ratio

This two-digit number represents the tire’s height-to-width ratio. Aspect ratios of 50 or lower suggest a shorter sidewall, which results in better steering response and overall handling.

Maximum Permissible Inflation Pressure

The maximum permissible inflation pressure is the highest amount of air pressure your tire should ever bear. It’s an essential factor in maintaining your tire’s health.

Nominal Width

These three digits indicate your tire’s width in millimeters from sidewall to sidewall. The larger the number, the wider the tire, which affects your vehicle’s grip on the road.

Rim Diameter Code

This two-digit number indicates your rim diameter in inches. Knowing this helps ensure your tire fits snugly and securely on your wheel.

Temperature &  Traction Ratings

The tire temperature rating gauges its resistance to heat, while the tire traction rating reveals how well it can bring your car to a stop on wet pavement. These two elements are crucial for a safe and reliable ride in extreme weather conditions.


The treadwear rating tells you how long your tires should last and should coincide with the manufacturer’s warranty. A higher number indicates a longer lifespan, saving you from frequent tire replacements.

U.S. DOT Tire Identification Number

Starting with “DOT,” this number assures your tire meets all federal standards. The following digits indicate your tire’s manufacturing details, including the plant code and the week and year it was built. These numbers are essential for recalls in case of a tire defect.

Your Tire Speed Rating & Load Index

Getting to know your car’s tires also involves understanding critical details like the speed and load ratings. Your tire’s speed rating tells you the highest speed your tire can handle, usually ranging from 99 mph to over 186 mph. 

The speed rating system was developed to ensure optimal tire performance. Interestingly, not all tires are required to display this information. The load index, a two to three-digit number that shows how much weight each tire can carry, goes hand in hand with the speed rating.

Initially, the system was about setting limits, like a top speed category. As tires improved, they added more categories, like the “Z” rating for top-tier speed. You might find these numbers in different places, from your car manual to the tire sidewall. Recent standards make it easier, as most tires now have the speed rating and load index.

Don’t Forget Your Spare

Knowing the ratings on your spare tire is essential for ensuring it’s reliable when you need it most. Spare tires, often overlooked, can age over time due to various factors like service, storage, and environmental conditions.

Spare tires are especially prone to aging because they get replaced less often. If your vehicle has a full-size spare, it’s recommended not to use it as a regular replacement for worn tires, except in emergencies like a flat tire.

Tire Inspection Service in Jacksonville, FL

Understanding your tires is the key to a safer drive, and at Big Chief Tire, we’ve decoded the essential elements for you so you can make informed decisions about your vehicle. Take the next step towards a safe driving experience by scheduling a tire inspection today.

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