Tires, Wheels and Axle Ratio

These calculators cover tire and wheel changes. Type a tire size to get its diameter and revolutions, compare it with new sizes, convert wheel offset to backspacing, or solve axle ratio against speed and engine rpm.

Tools in this group

• Axle Ratio Calculator — Solve for speed, engine rpm, axle ratio or tire diameter, and see how a new tire size changes the effective ratio and the speedometer.
• Offset Rim Calculator (Wheel Offset and Backspacing) — Convert wheel offset to backspacing, or compare your current and new wheel to see how far the rim and tire move in and out.
• Tire Load Index Chart — Look up a load index in kilograms and pounds, read a full tire code, or enter the weight to carry and get the lowest load index that is enough.
• Tire Size Calculator — Type a tire size such as 285/75R16 or 33x12.50R15 to get its diameter, sidewall height, revolutions per mile and the metric or inch equivalent.
• Tire Size Comparison Calculator — Enter your original tire size and one or two new sizes to compare diameter, width, sidewall and revolutions per mile, and see the speedometer error.
• Tire Speed Rating Chart — Read a speed symbol or a full tire code, or enter your vehicle's top speed to find the lowest speed symbol that covers it.
• Wheel Bolt Pattern Chart — Measure two studs to find your bolt pattern, convert a pattern between mm and inches, or identify the thread of your lug nuts.