Differences within about 2% of your original tire's diameter are rarely noticeable day to day. Go further than that — a common move when "plus sizing" to a bigger wheel — and your speedometer, odometer, and effective gearing all start drifting measurably from what they were calibrated for.
Tire size comparison calculator, original vs new
Enter both tire sizes (width, aspect ratio, rim diameter) and this calculator computes each one's actual diameter and circumference from the standard sizing formula.
Speedometer error calculator, in plain numbers
See the percentage difference and a concrete example — if your speedometer shows 60 mph, this tells you what your actual speed is with the new tire size.
Plus sizing calculator, with an honest limit
These are theoretical values from nominal size specs, not a specific tire's exact real-world dimensions — actual size varies slightly by manufacturer, tread design, and inflation, so treat the result as an estimate.
