Choosing the Right Tire Size for Your Vehicle

Three places: the tire information placard on the driver's side door or door jamb, the vehicle owner's manual, and the sidewall of the tires currently on the car. The door jamb placard is the most reliable source — it lists the size recommended by the vehicle manufacturer along with the correct inflation pressure. If the tires currently fitted differ from the placard (for example, on a used vehicle where someone changed the size), the placard is the authoritative specification.

Each section of the code describes a specific dimension or construction characteristic:

• 235 — Section width in millimeters (the tire's widest point)

• 55 — Aspect ratio, meaning the sidewall height is 55% of the section width

• R — Radial construction, the standard for all modern passenger tires

• 18 — Rim diameter in inches, which must match your wheel exactly

Changing from the manufacturer-specified size should only be done with guidance from a trained tire professional. Altering the overall diameter affects speedometer accuracy, the clearance between the tire and wheel well, and potentially how the ABS and stability control systems behave. Changing the width can affect handling balance. Michelin recommends following the vehicle manufacturer's specifications, and any deviation should be assessed for compatibility before installation.

Yes, in both cases. A wider tire creates a larger contact patch, which generally improves dry grip but increases rolling resistance. A taller sidewall (higher aspect ratio) absorbs road impacts more but introduces more flex in corners. A lower-profile tire feels sharper in steering response but can be harsher over rough surfaces. The factory size represents the manufacturer's balance of these trade-offs for that specific vehicle. Changing size shifts that balance in ways that are worth understanding before committing.

For some vehicles, yes. A staggered fitment — wider tires at the rear than the front — is common on rear-wheel-drive performance cars and some sports models. It's intentional, matching the rear axle's greater power and torque loads. The vehicle's door jamb placard will list both sizes if the fitment is staggered. Staggered fitments restrict tire rotation options, since front and rear tires usually can't swap positions directly.

Not necessarily. On used vehicles, previous owners may have fitted a non-standard size. On new vehicles, the size on the sidewall should match the placard, but it's worth confirming. The placard on the door jamb is the definitive reference for what the vehicle manufacturer specifies. If there's a mismatch between the current tire size and the placard, ask a tire professional whether the existing size is compatible before replacing in kind.