One of the most frequent questions we get is “what size tire do you recommend?”. The most correct, but least awaited answer we can give is “It depends”. Because frankly, tire size doesn’t really mean a whole heckuva lot.
We’ve been taught, through some sort of mythical passdown of inaccurate information, that the first number in a tires size (let’s say, 275) is it’s width, in mm. If that were true, things would be simple. When you go into a store to buy a new shirt, you see the same phenomenon. Some firms clothing runs bigger (or smaller) than others. You may wear a 34 jean from one company, and a 36 from another. Modifying a car is similarly inconsistent, and rarely is simple. While the first number in a tires size CAN be it’s width in mm, it’s more often than not, a general target of width. Now, on an otherwise stock car, this doesn’t really matter. When you start altering suspension, dropping the car an inch (or more), fitting super wide, super low offset wheels, your margin for error decreases exponentially. As the Pauli Exclusion Principal generally states (and was reinforced by Einstein and many others), 2 objects cannot occupy the same physical space at the same time. So in the interest of avoiding tire contact with the body of the car, with suspension components, with the inner fender liners, etc, things become more complicated.
This pictue is one Kwame posted several years ago, and it illustrates the point perfectly.
If you saw the above picture, which tire would you say is bigger? The one on the left clearly. But on paper, the tire on the right is bigger. Both are mounted on the same 11.5 inch wide wheels. The tire on the left is a Michelin PS2, 295/30/19. The tire on the right is a Pirelli PZero, 305/30/19. If you’re trying to get more “stance”, or gain a bigger footprint, which would you rather have? The one with the bigger number on the receipt, or the one with the bigger physical dimension?
Here is another picture of the same above example: 295/30/19 PS2 on left, 305/30/19 PZero on the right
So what do you do? Check the manufacturers site! Everyone should have the physical dimensions of their tires, in inches, for every corresponding ‘size’ listed on their website.