Wheel & Tire Calculator

Wheel & Tire Calculator

Compare your current wheel & tire setup with a new one. See changes in diameter, poke, inner clearance, speedometer error and ride height.

Your existing setup

Your new setup

Quick Fitment Reference

Wheel Basics

Examples: 17x8 ET40, 18x9.5 ET22

  • Diameter – overall wheel size (inches)
  • Width – how wide the rim is
  • Offset (ET)
    • Higher ET = wheel sits further in
    • Lower ET = wheel pokes out more

Tire Basics

Example: 255/35R18

  • Width – 255 mm
  • Aspect ratio – 35% of width is sidewall height
  • Rim diameter – 18" wheel

Tire diameter changes ride height, arch gap and speedometer accuracy.

Fitment Tips

  • 0–5 mm extra poke: usually safe
  • 5–15 mm: popular “flush” fitment range
  • 15+ mm: aggressive; higher rubbing risk
  • Always confirm inner clearance to suspension and arms
  • Staying close to OEM rolling diameter is safest if unsure

Speedometer & Circumference

Your speedometer is calibrated for the stock tire circumference.

  • Bigger circumference = real speed is higher than indicated
  • Smaller circumference = real speed is lower than indicated

The calculator shows speedo error (%) and real speeds at 30 mph and 60 mph.

Diagram Explained

  • Left = outside (fender / arch)
  • Right = inside (suspension / strut)
  • Vertical dashed line = shared hub mounting face
  • Orange = existing setup
  • Blue = new setup

We draw the tire and rim separately so you can clearly see both rim size and tire size changes.