Ok, so you want to read your tire dimension. I promise you that absolutely anyone can do it. I’ll use two of our supercars and from there you will be able to read any tire dimension!
Let’s take the standard set up on our Ferrari 488 GTB, for example:
245/35R20 on 9 J x 20 in front
305/30R20 on 11 J x 20 at the rear
vs. the 911 GT3:
245/35 ZR 20 on 9 J x 20 in front
305/30 ZR 20 on 12 J x 20 at the rear
Interestingly, we can see that the cars both call for the exact same tire size in every dimension- it lightens the burden of our tech team since they can share these consumables!
The singular difference is that the GT3‘s rear wheel is 1″ wider than the 488– this makes sense given the car’s rear-engine/rear-drive layout. This means ever so slightly more tire kissing the ground, which means just that much more grip, to compensate for the added weight and power delivery duties of the rear end.
Now, onto what these numbers mean- we’ll dig into the front numbers as an example.
245 refers to the width of the tire in millimeters- some countries refer to this as the “section” of the tire. Our friends across the pond would refer to a 245 tire as a “245 section” tire. This number generally varies anywhere from 155 to 450 on most vehicles you will see on the road. For you math whizzes, the next figure makes use of this first one.
The number that follows after the slash refers to the sidewall height, in terms of percentage of the first number. Don’t make the common error of assuming this also means millimeters! This number fluctuates depending on the first, so some quick maths is required in order to calculate this figure. Typically passenger cars are in the 50-80 range, while sports cars are typically in the 20-45 range. Generally speaking, the higher the number the more “cushioned” the ride, as a result of the increased sidewall thickness.
The final number refers to the diameter- this number is perhaps the most self-explanatory but can be crucial if gotten wrong. Tires and wheels are not interchangeable in terms of diameter, so it’s crucial that right size tires are mounted on right size wheels. This can be a challenge for those with older or modified cars, so keeping wheel speed and other associated sensors in mind is crucial when modifying your car to non-standard wheel and tire sizes.
Bonus tip:
For those who are buying used tires (or even new ones for that matter), another number to look out for is the date code- this is a four-digit number typically stamped on the outside on the tire inside of an oval. This four-digit code will tell you the month and date that the tire was manufactured, so you can gauge the age of the tire.
A date code of 2820 means the tire was manufactured the 28th week of 2020, while a date code of 5218 means the tire was manufactured in 52nd the last week of 2018.
We hope you were able to learn something from this quick write up- check your tires if you’ve never done so before, and let us know what sizes you’re running!
Until next time, keep calm and drive on!