Tire Size Comparison Calculator

Tire size difference explained

The single most important number when comparing two tires is the overall rolling diameter difference. It drives everything else — speedometer reading, ABS calibration, gearing and clearance.

• ≤ 3%Safe replacement window. Most OEMs design within this tolerance.
• 3 – 5%Borderline. Speedometer drift becomes noticeable; consider recalibration.
• > 5%Not recommended without professional review. Affects ABS, gearing and clearance.

Going too large raises ride height, slows acceleration and risks fender contact. Too small drops ride height, makes the speedometer read high, and shortens effective gearing.

Speedometer error explained

Your speedometer counts wheel revolutions and assumes a fixed circumference. Change the tire's rolling diameter and that assumption breaks — real speed differs from indicated speed by the same percentage as the diameter change.

• · ABS and traction control calibration relies on wheel speed.
• · AWD drivetrains are extra sensitive — keep deltas under ~1%.
• · Many jurisdictions allow indicated ≥ true, but not under-reading.

Plus sizing guide

Plus sizing keeps overall diameter close to OEM while moving to a larger rim and lower-profile tire. Minus sizing does the reverse for winter wheels.

Trade-offs: sharper steering response and a more aggressive stance, at the cost of ride comfort, pothole resistance and slightly higher unsprung weight.

OEM tire fitment

OEM sizes are chosen to match your car's suspension geometry, braking, gearing and electronics. The safest replacements preserve rolling diameter first, then load index and speed rating.

• · Stay inside the manufacturer's stated size and tolerance.
• · Match or exceed load index and speed rating.
• · Verify rim width is in the tire's approved range.
• · Keep all four corners on matched circumferences for AWD.