A Roxburgh Park woman- who claims she was unaware her car’s speedometer had been changed from metric to imperial- has had her car impounded by police.

Fawkner Highway Patrol officers stopped the woman on Sydney Road in Campbellfield about 4.20pm on Tuesday, after allegedly detecting her grey Jeep Cherokee travelling at 137 km/h.

Sydney Road is an 80km/h zone.

Police said the woman, 38, believed she was travelling within the speed limit and said she was unaware the setting on her speedometer had been changed.

Police said the woman was driving at 85 miles per hour.

The car was impounded with $896 towing costs and the woman is expected to be charged with speed-related offences.