▶ Compare two tire sizes at a glance. Enter both specs and see the difference in diameter, circumference, sidewall and ride height, with a to-scale overlay so the size change is obvious. ▶ Check your speedometer. See how a new tire shifts your real speed versus the reading, plus an odometer-error percentage — the numbers that matter after an upsize. ▶ Find plus sizes. Enter a target and get alternate sizes within a few percent of the original diameter, grouped by rim so you can plan a clean plus-one or plus-two. ▶ Decode the markings. Load-index and speed-rating tables turn the numbers on the sidewall into kg and km/h, with P, LT and XL explained. ▶ Save your vehicles and share a result card. Works offline, no account needed. Results are for reference only. Fitment and clearance depend on your vehicle — always confirm with your owner's manual or a tire professional.