Speedometer Error

Calculate speed reading deviation

Current Tire

New Tire

Speedometer Error Result

-1.72%

The speedometer reads higher than your actual speed

DashboardActual

Example: when the speedometer shows100 km/hyour actual speed is

98.28 km/h

Speed Table

Indicated speed (km/h)	20	40	60	80	100	120	140
Actual speed (km/h)	19.66	39.31	58.97	78.62	98.28	117.94	137.59
Deviation	-0.34	-0.69	-1.03	-1.38	-1.72	-2.06	-2.41

Speed Chart

DashboardActual

Key Summary

Width: +10 mm (+4.65%)
Sidewall: -5.75 mm (-4.86%)
Diameter: -11.50 mm (-1.72%)
Circumference: -36.1 mm (-1.72%)
Revs / km: +8.3 rev/km (+1.75%)
Ground Clearance: -5.75 mm
Speedometer Error: -1.72%

Tire Comparison

Why does the speedometer deviate?

Tire size changes

Wheel revolutions per km change

The ECU still calculates using the original tire size

The speedometer reads a different value than actual

Safe to use

The diameter difference is within ±3% — safe for speedometer accuracy and ABS/traction control calibration.

Try simulating your own speed

Dashboard100km/h

Actual speed98.28km/h

Deviation-1.72

Frequently Asked Questions

Does changing tire size always affect the speedometer?

Only if the overall tire diameter changes. Same overall diameter with a different width/aspect ratio combination causes no speedometer error.

What does this deviation affect?

It affects the speedometer, odometer, trip computer, and can affect ABS/traction control calibration if the difference is large.

Should I choose a smaller or larger tire?

If the overall diameter gets smaller, the speedometer reads higher than actual; if larger, it reads lower than actual.

All Tools

Tire Size Calculator

Calculate and compare tire sizes

Plus / Minus Sizing

Find a matching size for a new wheel diameter

Wheel Fitment

Calculate offset and wheel position

Unit & Tire Converter

Convert units and tire sizes

Comparison & Reports

Compare multiple sizes and generate a report