Wheel & Tire Fitment Calculator
Enter your stock and new wheel and tire specs to instantly check whether the new setup will fit - including diameter change, speedometer error, and inner and outer clearance changes. Nothing uploaded.
Stock wheel & tyre
Arch clearance
New wheel & tyre
Fitment check
Learn more: wheel offset, fitment, and tire sizing
Understanding wheel offset and why it matters for fitment
Wheel offset (in millimeters) is the distance from the wheel's center line to the mounting surface. Positive offset moves the mounting surface outward (common for modern cars). Negative offset moves it inward (common for classic cars and deep-dish wheels). A wheel that is too positive or too negative will either rub the inside of the fender or stick out past the bodywork. Offset is critical for safe, legal fitment.
Tire size and sidewall height affect final wheel diameter
Tire size format (255/35/19) means 255mm width, 35 percent sidewall ratio, and 19-inch rim diameter. The sidewall height is calculated as 255mm times 0.35, which equals 89.25mm. The wheel's actual diameter is 19 inches (482.6mm) plus two sidewalls (2 times 89.25mm). Changing to a lower profile (e.g., 30 percent instead of 35) reduces sidewall height and final diameter, affecting speedometer accuracy and ride quality.
Clearance measurements: fender, suspension, and brake components
Fitment requires measuring clearance between wheel and fender, suspension arms, and brake components. The calculator gives hub-centric and lug-centric offsets for comparison. A spacer can adjust effective offset if needed, but adds complexity to your wheel assembly. Always test-fit wheels before finalizing any purchase or modification.
FAQ
What is positive vs negative wheel offset?
Positive offset means the mounting surface is pushed outward from the wheel centerline, bringing the wheel closer to the fender. Negative offset pulls the wheel outward past the centerline. Most modern cars use positive offset; drag racing and classic cars use negative (deep-dish) offset.
How does tire sidewall height affect wheel size?
Final wheel diameter equals rim diameter plus twice the tire sidewall height. A 19-inch rim with a 255/35 tire adds about 89mm of sidewall on each side, making the total diameter much larger than the rim alone. Switching to a lower profile tire (e.g., 255/30) reduces final diameter.
Can I use wheel spacers to change offset?
Yes, but spacers reduce bolt-centric stiffness and add weight to the wheel assembly. They are a workaround for fitment issues, not a perfect solution. Always use high-quality spacers designed for your vehicle and torque them to spec.