Tire specs are confusing! But reading the tire size isn’t. To be honest, tires are one of those niches where you kind of just have to know about from doing it.
The good news is that you have pages like these to print off that tell you everything you need to know about any specific set of tires.
I’ve mounted up a lot of tires, and after staring at thousands of different tire sidewalls, I’ve deduced a plan to help you know what to do when reading a tire.
Hilarious, some of the biggest arguments I’ve ever seen working as a mechanic are between the parts guy who deliberately gets the technician’s tire sizes or model wrong. There you go, even professionals have plenty of mix-ups when it comes to tire spec variables.
So, before you do read tire labels, I recommend you read this pro guide on how to read a tire:
What You Need To Know About How To Read A Tire
Tires do have a lot of specs, but they’re not infinite. Learning how to read and understand your tire sidewalls will keep you from mounting crossover SUV/light truck tires on a full-sized pickup. Here’s a fat list of potential specs found printed on the sidewalls of tires:
‘P’, ‘LT’, ‘R’, and any other letter that comes before the tire size
Before the first tire size, you’ll likely see either a ‘P’ or ‘LT’ for ‘passenger’ and ‘light truck’. Passenger car tires typically have a lighter load rating while light truck tires are suitable for towing and carrying heavy loads. You might also see ‘ST’ for special trailer tires.
The ‘R’ that typically comes before the third tire size number (rim diameter) means that the tire is a radial design rather than a biased design.
Tire size numbers
The set of three tire size numbers (i.e., 225/75R17) is good to know about when dealing with tires, and the most important to get right when buying a new set of tires.
Plug in your vehicle’s info to sites like Tire Rack to get a complete list of tire size numbers compatible with your vehicle.
I’ve outlined the tire sizes for traditional car and truck tires, but flotation tire sizes also exist for golf cart and ATV tires that are measured in only inches.
What is the first tire size number?
The first three-digit tire size number is the width of the tire in millimeters. The width of your tire treads determines how much surface area the tires cover across the surface of the road.
What is the second tire size number?
The second tire size number is the tire’s aspect ratio or sidewall height. The aspect ratio number is a height-to-width ratio.
In other words the higher the aspect ratio number, the taller the sidewalls are going to be. In terms of road tires, shorter sidewalls rock ‘n’ roll at fast speeds while taller sidewalls tend to be smoother over the bumps.
What is the third tire size number?
The third tire size number is the wheel diameter in inches.
Now, why do we use millimeters for the tire width and inches for the tire size? Who the hell knows…could have something to do with the collaboration of automotive engineering between the USA and the rest of the world.
You’ll also typically see an ‘R’ before the third tire size indicating that it’s a radial tire. Almost all car tires nowadays are radial construction compared to the old-school bias ply tires that are still heavily used today in both construction and agriculture.
‘Inside’ and ‘outside’ labels
Asymmetrical tread designs mean that the mechanic must mount the tire on the correct side of the wheel spokes. You should always keep an eye out for those ‘inside’ and ‘outside’ labels before mounting up a set of tires.
Asymmetrical designs are utilized to improve road traction. For example, many all-season tires have a flow pattern for water exits to reduce hydroplaning.
Directional tires always have aesthetic tread patterns, and arrows are one thing I always look out for when mounting up a set of treads.
Directional tires are passenger and driver’s side specific.
Tire speed rating/Speed Symbol
Speed ratings are a European standard to determine the max speed of a tire under load. These speed ratings range from ‘A1’ to ‘(Y)’. The tire’s maximum speed in MPH or KM/H is associated with each letter.
For example, a tire rating of ‘H’ has a maximum speed of 130 MPH. You can be less afraid of having a bit of a lead foot. Obey the speed limits, people!
Tire speed rating and load index (below) grouped is also referred to as the service description.
Tire load index/Load rating/Load capacity
The maximum load rating is a number representing the amount of weight the tire can support. Why don’t they just use the actual weight limit in pounds or kilos? Probably because they’re individual tires, so if you’re driving in a sedan, you’d have to times that number by four. On the other hand, if you’re driving a truck with duel-rear wheels, then the variables start to change.
Max PSI recommendations
Remember, tires have max PSI ratings for cold pressure. This is the maximum air pressure that your tire can safely hold under load.
Please remember, your car doesn’t perform near as well with the max amount of air pressure. Yes, higher PSI improves fuel efficiency, but it also causes problems like decreased handling ability and uneven treadwear in the middle of the tread.
It’s important to always use the driver’s side door jamb recommendations for correctly inflating your tires to spec.
ECE type approval mark and number
ECE stands for the Economic Commission for Europe, and this marking is found on a tire that is approved for use in Europe.
US Dot Tire Identification Number
Just like Europe, the United States has a safety standard code for tires. You’ll notice a DOT number on most name-brand tires.
More importantly, if you don’t see a DOT on your tires it means they’re not suitable for American highways (like some offroading/agricultural tires, for example).
Many tire brands, like General Altimax RT43, have treadwear indicators on the sides of the treads that help the vehicle owner quickly notice alignment issues and other suspension problems that cause uneven treadwear.
If you see ‘reinforced’ or ‘XL’ marked on the tire, it means that these have reinforced beading for extra heavy-duty use.
Tire ply composition/Materials used
It’s not uncommon for a tire manufacturer to add tire ply composition information to the sidewall to keep consumers informed.
Uniform Tire Quality Grading (UTQG)
UTQG ratings are given to tires by the US Department of Transportation National Highway Traffic Safety Administration.
These ratings let consumers compare tires by:
- Treadwear grade
- Temperature grade
- Traction grade
The last four numbers in the DOT code are the tire’s manufacturing week and year. For example, if the last four numbers read 2519, then that means the tires were made in the 25th week of 2019.
Mechanics always look for the manufacturing year because it’s not safe to drive on old tires. Specifically, if the tires are more than 6 years old then places like the NHTSA highly recommend against using them. At a maximum, you should replace old tires after they’re 10 years old.
Runflat tires are designed to be driven at slower speeds when completely deflated. How to identify a run-flat tire? Every tire is different, that’s why you need the internet to perform a quick search about your specific set of tires.
Continental prints an SSR (self-supporting run-flat) on their tires’ sidewalls, Michelin uses ZP (zero pressure), Pirelli puts RSC (reinforced sidewall construction) or Run-Flat, Bridgestone labels RFT (run-flat tire), and that’s just to name a few of the top brands.
The three-peaked mountain snowflake symbol
The three-peaked mountain snowflake symbol printed on tire sidewalls indicates that the tire is adequate for light snowy conditions based on temperature resistance and traction.
But keep in mind, even some all-season tires have this symbol, so the snowflake symbol doesn’t exactly mean that the tire is a dedicated winter tire.
Supplies You’ll Need For How To Read A Tire
Your attention and objective thinking are the only real way to be accurate when reading specs.
When reading a tire, you need to know what you’re looking for, and why you’re looking for it. Want to compare UTQG ratings between tires? Then look for temperature, treadwear, and traction grades.
Are you checking the compatibility of a tire for a specific vehicle? That’s where you’ll want to check tire size. Mounting up a new set? Don’t forget to identify directional arrows and ‘inside’/’outside’ labels.
Don’t get all googly-eyed trying to read your tire size numbers. If you can’t see what’s printed exactly, ask someone to make sure you’re reading the tire correctly, or even better, search for a photo of the tire sidewall when it’s new.
This is a situation where you’ll want to use your phone or laptop to learn all about your specific set of tires.
Watching an instructional video always helps:
How To Read A Tire (5-Step Guide)
- Learn the three main tire size numbers
- Learn speed rating and load rating numbers
- Learn to decipher between symmetrical/asymmetrical tread patterns
- Check the owner’s manual for your vehicle’s additional tire specifications
- Plug-in vehicle info into sites like Tire Rack
Step 1: Learn the three main tire size numbers
The first thing to look for when looking to buy new tires is the current tire size that’s on your vehicle. I’ve outlined in-depth above what each tire size number means and left a quick overview below:
Passenger vehicles/Truck tire size numbers (225/75R17)
The first number = tire width (millimeters)
The second number = aspect ratio (sidewall height)
The third number = rim diameter (inches)
ATV/Floating tire size numbers (33X13.5R17)
The first number = overall diameter (inches)
The second number = section width (inches)
The third number = rim diameter (inches)
Step 2: Learn speed rating and load rating numbers
Always check the speed capability before buying the tire. If you want high-performance tires, you’re going to want higher speed ratings like ‘Y’.
However, fast tires aren’t always the best option. You should also remember that tires with more reasonable speed ratings like Michelin Defender’s ‘H’ speed rating (130 MPH) have slightly softer rubber that adds to ride comfort.
Step 3: Check for symmetrical/asymmetrical tread patterns, directional tires, staggered tire sizes, etc.
Always check for ‘inside’ and ‘outside’ labels, directional arrows, and staggered tires before attempting to mount tires onto your vehicle.
It’s always hilarious when a technician accidentally mounts the skinny front tire onto the thicker rear wheel. These are the important numbers to know as a technician, but they’re also important so the consumers can remind the mechanics when the work pace gets fast in the shop.
Step 4: Check the owner’s manual for your vehicle’s tire specifications
Yes, it’s still possible to put the wrong type of tires on your car. Aside from the actual tire size, you need to consider factors like speed rating, load index, and the proper tread pattern for your specific style of driving.
In general, the owner’s manual provides a lot of useful information that you don’t need until the problem arises. For example, a warning light might appear on the dash that you can’t decode right off the bat. Warning light appearances and tire issues/replacements are those times when you might need to flip through the manual real quick.
Step 5: Plug in vehicle info to sites like Tire Rack
Lucky us, we have technology like computer programs that will tell you any set of tires that will fit on your specific car.
On most machines, you’ll find a tire information sticker on the inside of the driver’s side door panel that tells you everything you need to know about your tires.
Other Valuable Resources on How To Read A Tire
If you’re reading this article, I’m assuming you already know how to inspect your tires for even treadwear, set the tire pressures to the recommended PSI, and other basic tire maintenance.
Are you deciphering every little number and letter on your tires? This guide helped you a lot. Now it’s time to keep learning about your tires! Stay safe and have fun.