A method for use in an Adaptive Cruise Control, ACC, system of a vehicle, for adjusting a variable time gap (t) to be kept to a preceding vehicle, based on a road slope (α), wherein the method comprises: determining geographical position of the vehicle; determining driving direction of the vehicle; determining the road slope (α) of the road in front of the vehicle in the determined driving direction; and adjusting the variable time gap (t) based on the determined road slope (α) of the road in front of the vehicle by: increasing the variable time gap (t) when the road slope (α) is negative, indicating downhill; decreasing the variable time gap (t) when the road slope (α) is positive, indicating uphill, wherein the method is further comprising: determining the road slope (β) of the road at the determined geographical position of the vehicle; characterized in that the variable time gap (t) is adjusted based on the difference between the determined road slope (β) at the vehicle and the determined road slope (α) in front of the vehicle by: increasing the variable time gap (t) when the determined road slope (α) in front of the vehicle is smaller than the determined road slope (β) at the vehicle; decreasing the variable time gap (t) when the determined road slope (α) in front of the vehicle exceeds the determined road slope (β) at the vehicle. determining geographical position of the vehicle; determining driving direction of the vehicle; determining the road slope (α) of the road in front of the vehicle in the determined driving direction; and adjusting the variable time gap (t) based on the determined road slope (α) of the road in front of the vehicle by: increasing the variable time gap (t) when the road slope (α) is negative, indicating downhill; decreasing the variable time gap (t) when the road slope (α) is positive, indicating uphill, wherein the method is further comprising: determining the road slope (β) of the road at the determined geographical position of the vehicle; characterized in that the variable time gap (t) is adjusted based on the difference between the determined road slope (β) at the vehicle and the determined road slope (α) in front of the vehicle by: increasing the variable time gap (t) when the determined road slope (α) in front of the vehicle is smaller than the determined road slope (β) at the vehicle; decreasing the variable time gap (t) when the determined road slope (α) in front of the vehicle exceeds the determined road slope (β) at the vehicle. increasing the variable time gap (t) when the road slope (α) is negative, indicating downhill; decreasing the variable time gap (t) when the road slope (α) is positive, indicating uphill, wherein the method is further comprising: determining the road slope (β) of the road at the determined geographical position of the vehicle; characterized in that the variable time gap (t) is adjusted based on the difference between the determined road slope (β) at the vehicle and the determined road slope (α) in front of the vehicle by: increasing the variable time gap (t) when the determined road slope (α) in front of the vehicle is smaller than the determined road slope (β) at the vehicle; decreasing the variable time gap (t) when the determined road slope (α) in front of the vehicle exceeds the determined road slope (β) at the vehicle. increasing the variable time gap (t) when the determined road slope (α) in front of the vehicle is smaller than the determined road slope (β) at the vehicle; decreasing the variable time gap (t) when the determined road slope (α) in front of the vehicle exceeds the determined road slope (β) at the vehicle.