The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support ExtremePSI
Please Support Morrison Fabrication

How To: Reading AND Understanding Tire Sizes/Specs 101

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Many people don't understand what the true meaning of the numbers embedded on your tires even represent. Not only will this misunderstanding of tire sizes risk damage to your car, it can even land you a speeding ticket when you don't think you were! This tutorial will help give you a better understanding of how to read the numbers, and how they will affect your ride.


1.) The first MUST with understanding how tire sizes/specs work is a breakdown of the individual numbers within the size set. (Will be using metric measurements for this tutorial)
Lets use 225/45R17 as an example. (Don't worry about the "R" until later)


The first number of the set "225" is known as the Section Width. The measures (in millimeters) the distance across the widest point of the outer sidewall to the widest point of the inner sidewall. This measurement is taken when the tire is MOUNTED on its corresponding width wheel. Not "Stretched or Stanced"
You must be logged in to view this image or video.




The next number in our example is "45". This is where a lot of people get confused and have a general misunderstanding. This number is known as the "aspect ratio" and signifies the height of the tire in correspondence to the first number, the width (225). Confused!? Dont be, its simple. The "45" number in our example simply states that the sidewall is 45% of the width of the tire! Duh right!?
You must be logged in to view this image or video.




The last number of the three is the "17". This is the simplest number, as it represents the tire diameter. If a tire has a 17 embedded on it, NEVER attempt to match it to another rim of a different size. Another note, generally the larger the diameter tire, the higher the cost of the tire.
You must be logged in to view this image or video.



The "R" circled in red in this example stands for "Radial" and just states that the tire is radial ply construction.

You must be logged in to view this image or video.




The FIRST letter within the pair of letters (using the picture below) signifies the speed rating. In this exmaple there is "ZR". We already know the "R" stands for radial. But in this example there is a "Z" before it. Today, the ONLY tires that have a speed rating in-between the aspect-ratio and the diameter is "Z" rated tires. Most tires of a different speed rating will show the speed rating next to the load index, like "225/45R17 89V". This is probably one of the most important things to understand about your tires, so listen up. The speed rating tells you what the maximum SAFE speed that tire was designed to handle. Does this mean if you go 120MPH with a "T" rated tire (rated to 118MPH) it will explode and kill you? No, most likely not. But anything past the maximum speed GREATLY increases the risk of catastrophic failure!!! (will include common speed ratings and corresponding maximum MPH at end of tutorial).

Z rated tires shown here:
You must be logged in to view this image or video.


Other rated tires shown here:
You must be logged in to view this image or video.




The last part of this section of the tire is the "Load Index". This is normally a double-digit number that displays what each individual tires designed load carrying capacity, (use above picture for reference). Ill place a chart at the end displaying what each load number relates to in weight.




2.) Now that we understand the size, speed, and load specs of our tire and it can kill us if misused, we are ready to move on to the UTQG rating.


The UTQG or Uniform Tire Quality Grade is a test which is performed to most tires upon creation. The results are all figured out by a bunch of really smart people and turn in this:

Edit: These tests are performed by each manufacturer, so two tires of the same specs but different companies could have very different actual results. There is no industry standard. (thanks tylersevo)

You must be logged in to view this image or video.



The first part of the UTQG is the Treadwear. The treadwear is tested on a private test loop (just like in Gran Turismo). The car drives about 7200 miles per test. If the tires are completely worn (not like threads and bands showing) but at end of service life after the 7200 mile test, they are given a 100 treadwear rating. A 200 treadwear rating would be given if the tire had 50% tread left at the end of the test, (and so on, and so on...).

You must be logged in to view this image or video.




The next section of the UTQG is the Traction rating. Yes!!!, how sticky my tires are for drag racing!!! NOPE. Not even close, sorry. Yet another misconception. This signifies how well the tire stops/grips in a WET STRAIGHT BRAKING condition only. Not turning, not accelerating. The shorter the distance, the better the rating. (AA,A,B,C) Seen here:

You must be logged in to view this image or video.




The last part of the UTQG is the Temperature rating. This one is kind off boring yet very important. When a tire is rotating, what does it create?! If you said heat, your correct. This letter, (only A,B, or C) signifies how well the tire can dissipate the heat created by the rotational friction. If a tire is rated a "C", it can only effectively dissipate heat up to about 90MPH. An "A" rating is good for speeds above 115MPH. MOST (not all) performance tires will have an "A" rating. Just be sure to check because it is a very important factor of your tires. Example:

You must be logged in to view this image or video.





There are many other numbers, variations, etc. of tires out there. This is only here to provide you with the basic information required to understand what your tires are designed to do.


Here are the promised speed ratings:

You must be logged in to view this image or video.


And load ratings:

You must be logged in to view this image or video.
 
Last edited:
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top