The Ultimate Guide to Plus-Sizing Your Tires (Safely)

One of the most popular upgrades for any vehicle is a new set of larger, stylish wheels. It completely transforms the look of the car, filling up the wheel arches and giving it a premium, aggressive stance.

But you can't just buy massive wheels, slap any tire on them, and call it a day. If you do, your tires will rub against the fenders, your speedometer will break, and your transmission might even shift weirdly.

To do it right, you need to use a technique called Plus-Sizing.

What is Plus-Sizing?

Plus-sizing is the art of increasing your wheel diameter (getting bigger rims) while simultaneously decreasing your tire's sidewall height.

The ultimate goal of plus-sizing is to keep the overall diameter of the tire exactly the same as the factory tire.

If your factory tire is 25 inches tall, your new wheel and tire combo must also be roughly 25 inches tall. This ensures that your car's computer, speedometer, and suspension geometry all continue to function exactly as the engineers intended.

The Plus-Size Formula

In the tire world, you'll hear terms like "Plus 1", "Plus 2", and "Plus 3". Here is what they mean in plain English:

Plus 1

You increase the wheel diameter by 1 inch (e.g., going from 17" to 18" wheels).
You increase the tire width by 10mm (e.g., from 215 to 225).
You decrease the aspect ratio (sidewall) by 10 points (e.g., from 55 to 45).

Plus 2

You increase the wheel diameter by 2 inches (e.g., going from 17" to 19" wheels).
You increase the tire width by 20mm (e.g., from 215 to 235).
You decrease the aspect ratio (sidewall) by 20 points (e.g., from 55 to 35).

The Pros and Cons of Plus-Sizing

The Good Stuff:

Better Handling: Shorter sidewalls are stiffer. When you take a corner, the tire won't flex and roll as much, giving you sharper, more responsive steering.
Incredible Looks: Bigger wheels simply look better. It’s the easiest way to make a cheap car look expensive.
Bigger Brakes: If you want to install a high-performance brake kit, you usually need bigger wheels to clear the massive brake calipers.

The Bad Stuff:

Harsher Ride: Because the sidewall is shorter, there is less rubber and air between your wheel and the road. You are going to feel potholes and bumps significantly more.
Pothole Damage: With less rubber protecting the rim, hitting a deep pothole is much more likely to bend or crack your expensive new wheels.
Cost: Bigger wheels and low-profile tires are generally much more expensive than standard sizes.

The 3% Golden Rule

When you are playing around with plus-sizing, you must follow the 3% rule: Your new tire's overall diameter should never be more than 3% larger or smaller than your original factory tire.

If you go past 3%, you risk destroying your car's ABS (Anti-lock Braking System) calibration, messing up your speedometer, and causing severe rubbing issues in your wheel wells.