Tire Size Calculator & Offset

Tire Size Calculator compares two tire sizes and shows what changes: overall diameter, sidewall, circumference, ride height, speedometer error and, new in this version, wheel offset and rim width. ▶ TIRE SIZE COMPARISON • Current vs new size, e.g. 225/45R17 → 235/40R18 or 265/70R17 → 33x12.50R17 • Overall diameter, sidewall height, circumference, ride height, revs per km or mile • Both tires drawn to scale on one picture • Metric and flotation (inch) sizes, mm or inch display ▶ SPEEDOMETER ERROR • Real speed at an indicated 30, 50, 60, 80, 100, 120 km/h • In inch mode: 20, 30, 40, 50, 60, 70, 80 mph • Odometer error in percent ▶ PLUS SIZE FINDER • Metric sizes (widths 135–355, rims 13–24) within ±3% of the base diameter • Grouped by rim size with a Plus 1 / Plus 2 badge • Tap a size to compare it with the base size ▶ WHEEL OFFSET (ET) AND RIM WIDTH • Rim width 4 to 13 J, offset −50 to +70 mm, for the old and the new wheel • How far the outer edge moves out (poke) and the inner edge moves toward the suspension • Tire edge change and approximate backspacing • To-scale cross-section from the hub face ▶ SIDEWALL CODES • P, LT, XL and RF explained • Speed rating table L to (Y), km/h and mph • Load index 60 to 130, kg and lb ▶ MY GARAGE • Save the tire sizes of your cars, load one with a tap Calculations run on the phone, no sign-in. The numbers are geometric estimates from the size markings: the mounted tire width depends on the rim, and backspacing assumes a 12.7 mm flange. The app does not decide whether a wheel fits. Check fitment and clearance with the vehicle manual or a tire shop.

New Side view on the Compare tab: the current and new tire are drawn next to each other at the same scale, with the theoretical radius change and the sidewall and rim difference. Fixed: on small phones with the 3-button navigation bar, the last row of the size picker was half hidden. Fixed: on the 5th launch the app opened a store web page by itself; it no longer does.