https://sidewallmath.com/Compare tire sizes side by side, convert metric sizes to inches, check speedometer error after a size change and decode load index and speed ratings.en-ushttps://sidewallmath.com/tools/tire-size-comparison/https://sidewallmath.com/tools/tire-size-comparison/Wed, 11 Nov 2026 09:00:00 -0700Compare two tire sizes side by side: diameter, width, sidewall, circumference, revolutions per mile, speedometer difference and the 3% plus-sizing check.https://sidewallmath.com/tools/tire-size-calculator/https://sidewallmath.com/tools/tire-size-calculator/Wed, 11 Nov 2026 09:00:00 -0700Convert any tire size like 225/65R17 or 33x12.50R15 to overall diameter, width, sidewall height, circumference and revolutions per mile, with the math shown.https://sidewallmath.com/tools/speedometer-error-calculator/https://sidewallmath.com/tools/speedometer-error-calculator/Wed, 11 Nov 2026 09:00:00 -0700See how far off your speedometer and odometer read after changing tire size, with a table of indicated vs actual speeds in mph or km/h.https://sidewallmath.com/tools/load-index-speed-rating/https://sidewallmath.com/tools/load-index-speed-rating/Wed, 11 Nov 2026 09:00:00 -0700Decode the load index and speed rating on a tire, such as 91V or 121/118S, into kilograms, pounds, km/h and mph, with full charts from tire maker tables.https://sidewallmath.com/guides/tire-tread-depth-and-pressure/https://sidewallmath.com/guides/tire-tread-depth-and-pressure/Wed, 11 Nov 2026 09:00:00 -0700How to check tire pressure and tread depth the way NHTSA recommends: cold readings, the door label pressure, the 2/32 inch limit, wear bars and the penny test.https://sidewallmath.com/guides/tire-age-and-dot-date-code/https://sidewallmath.com/guides/tire-age-and-dot-date-code/Wed, 11 Nov 2026 09:00:00 -0700How to find a tire's manufacture date from the last four digits of the DOT code, why tire age matters, and what NHTSA says about replacing older tires.https://sidewallmath.com/guides/plus-sizing-rules/https://sidewallmath.com/guides/plus-sizing-rules/Wed, 11 Nov 2026 09:00:00 -0700Four rules for changing tire or wheel size from a tire maker bulletin: load capacity, inflation pressure, speed rating and rolling circumference.https://sidewallmath.com/guides/how-to-read-a-tire-sidewall/https://sidewallmath.com/guides/how-to-read-a-tire-sidewall/Wed, 11 Nov 2026 09:00:00 -0700What every marking on a tire sidewall means: size, load index, speed rating, DOT tire identification number, UTQG treadwear, traction and temperature grades.https://sidewallmath.com/guides/common-tire-sizes-chart/https://sidewallmath.com/guides/common-tire-sizes-chart/Wed, 11 Nov 2026 09:00:00 -0700A chart of common car, SUV and pickup tire sizes with calculated diameter, width, sidewall height and revolutions per mile, plus how to use it to compare sizes.