Ever wondered how your car knows exactly how many kilometers it has traveled? The answer lies in electronic sensors connected to your wheels. Modern vehicles use wheel speed sensors (WSS) or vehicle speed sensors (VSS) that count the number of wheel rotations. The Electronic Control Unit (ECU) then multiplies these rotations by the tyre’s circumference to calculate the distance. This data is displayed on your odometer and speedometer.

What happens if you change tyre size?

• Bigger tyres: Cover more distance per rotation. Result – your speedometer shows lower than actual speed, and the odometer under-reports kilometers.

• Smaller tyres: Cover less distance. Result – your speedometer shows higher, and the odometer over-reports kilometers.

For example, at a displayed 60 km/h, your actual speed could be 63+ km/h with larger tyres.

How to fix this?

• ECU programming: Dealers can update tyre size settings in the system.

• OBD-II devices: Handy tools that reprogram your car’s computer.

• Speed calibrators: External devices that correct sensor signals.

Experts suggest keeping tyre size changes within ±5% of original to avoid affecting safety systems like ABS, transmission shifts, and fuel economy.

In short: Tyre size directly impacts your car’s accuracy—so always recalibrate after a change.