A method is provided for estimating the effective wheelbase length of a trailer in a vehicle combination including a towing vehicle and at least one towed trailer. The method includes driving the vehicle combination forwards, determining the speed of the vehicle combination, determining the steering angle of the towing vehicle, determining the steering angle of each towed trailer, determining the yaw rate of the towing vehicle and the yaw rate of the towed trailer or determining the articulation angle for each towed trailer, and using the determined values to calculate a value for the effective wheelbase for each towed trailer. An arrangement for estimating the effective wheelbase length of a trailer in a vehicle combination is also disclosed.