Tyre Upsize Calculator (\u00b13% Rule)
Bigger rims? Check the new size keeps overall diameter within the safe \u00b13% window, and see your speedo error.
Current vs new
The change
+3.0%
Diameter change
103.0 km/h
Actual speed at indicated 100
💡 Outside the safe window (3.0%). Your speedometer, odometer and ABS calibration will be off - pick an aspect ratio that brings the diameter within ±3%.
Classic safe upsizes: 185/65 R15 → 195/60 R16, 215/60 R16 → 215/55 R17. Wider = more grip but heavier steering and slightly higher fuel use.
Frequently asked questions
Why does the ±3% rule exist?
Your speedometer, odometer and ABS are calibrated to the original rolling diameter. Beyond ~3%, readings and braking calibration drift meaningfully.
Does upsizing improve the car?
Wider tyres grip better and look the part, at the cost of some fuel, steering lightness and ride comfort. Balance, not maximum, wins.