How tire size calculator Works
Reading the code
In 225/65R17: 225 is section width in millimeters, 65 is the sidewall as a percentage of width (not millimeters!), and 17 is the wheel diameter in inches. Sidewall height = 225 × 0.65 = 146 mm. Overall diameter = wheel + 2 × sidewall = 17 + 2 × (146 ÷ 25.4) = 28.5 inches.
Why diameter is the number that matters
Your speedometer, odometer, gearing, and ABS calibrations all assume the stock diameter. Stay within ±3% and everything behaves. The classic plus-sizing trap — bigger wheel, lower profile — keeps diameter constant only if the aspect ratio drops to match, which is exactly what the calculator checks for you.
What each change does
- Taller diameter (+3%+): speedometer reads slow (you're going faster than indicated), odometer under-counts miles, sluggish acceleration, possible rubbing at full lock.
- Shorter diameter: speedo reads fast, odometer over-counts, quicker acceleration feel, more wheel gap.
- Wider section at same diameter: more grip and looks, slightly worse fuel economy and hydroplaning resistance, and fitment depends on wheel width and offset — verify with a tire professional.